arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4): more undefined references to `__bad_cmpxchg' follow

arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4): more undefined references to `__bad_cmpxchg' follow

[Naresh Kamboju]

The arm builds failed on Linux next with gcc-13 and clang-18.

Config: arm imx_v6_v7_defconfig - failed

Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>

Build log:
-----
arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function
`rcu_trc_cmpxchg_need_qs':
update.c:(.text+0x348): undefined reference to `__bad_cmpxchg'
arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function
`rcu_read_unlock_trace_special':
update.c:(.text+0x41c): undefined reference to `__bad_cmpxchg'
arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function
`trc_read_check_handler':
update.c:(.text+0x4b0): undefined reference to `__bad_cmpxchg'
arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function `trc_inspect_reader':
update.c:(.text+0x1518): undefined reference to `__bad_cmpxchg'
arm-linux-gnueabihf-ld: update.c:(.text+0x1548): undefined reference
to `__bad_cmpxchg'
arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4):
more undefined references to `__bad_cmpxchg' follow
make[3]: *** [/builds/linux/scripts/Makefile.vmlinux:34: vmlinux] Error 1

metadata:
  git_describe: next-20240529
  git_repo: https://gitlab.com/Linaro/lkft/mirrors/next/linux-next
  git_short_log: 9d99040b1bc8 ("Add linux-next specific files for 20240529")
  job_url: https://tuxapi.tuxsuite.com/v1/groups/linaro/projects/lkft/builds/2h944W0LTbtfMPlDNiOq17hXpQ8

Links:
 - https://qa-reports.linaro.org/lkft/linux-next-master/build/next-20240529/testrun/24129266/suite/build/test/gcc-13-imx_v6_v7_defconfig/history/
 - https://qa-reports.linaro.org/lkft/linux-next-master/build/next-20240529/testrun/24129266/suite/build/test/gcc-13-imx_v6_v7_defconfig/log


--
Linaro LKFT
https://lkft.linaro.org

arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4): more undefined references to `__bad_cmpxchg' follow

[Naresh Kamboju]

The arm builds failed on Linux next with gcc-13 and clang-18.

Config: arm imx_v6_v7_defconfig - failed

Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>

Build log:
-----
arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function
`rcu_trc_cmpxchg_need_qs':
update.c:(.text+0x348): undefined reference to `__bad_cmpxchg'
arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function
`rcu_read_unlock_trace_special':
update.c:(.text+0x41c): undefined reference to `__bad_cmpxchg'
arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function
`trc_read_check_handler':
update.c:(.text+0x4b0): undefined reference to `__bad_cmpxchg'
arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function `trc_inspect_reader':
update.c:(.text+0x1518): undefined reference to `__bad_cmpxchg'
arm-linux-gnueabihf-ld: update.c:(.text+0x1548): undefined reference
to `__bad_cmpxchg'
arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4):
more undefined references to `__bad_cmpxchg' follow
make[3]: *** [/builds/linux/scripts/Makefile.vmlinux:34: vmlinux] Error 1

metadata:
  git_describe: next-20240529
  git_repo: https://gitlab.com/Linaro/lkft/mirrors/next/linux-next
  git_short_log: 9d99040b1bc8 ("Add linux-next specific files for 20240529")
  job_url: https://tuxapi.tuxsuite.com/v1/groups/linaro/projects/lkft/builds/2h944W0LTbtfMPlDNiOq17hXpQ8

Links:
 - https://qa-reports.linaro.org/lkft/linux-next-master/build/next-20240529/testrun/24129266/suite/build/test/gcc-13-imx_v6_v7_defconfig/history/
 - https://qa-reports.linaro.org/lkft/linux-next-master/build/next-20240529/testrun/24129266/suite/build/test/gcc-13-imx_v6_v7_defconfig/log


--
Linaro LKFT
https://lkft.linaro.org

_______________________________________________
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Re: arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4): more undefined references to `__bad_cmpxchg' follow

[Russell King (Oracle)]

On Thu, May 30, 2024 at 05:50:52PM +0530, Naresh Kamboju wrote:
> The arm builds failed on Linux next with gcc-13 and clang-18.
> 
> Config: arm imx_v6_v7_defconfig - failed
> 
> Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
> 
> Build log:
> -----
> arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function
> `rcu_trc_cmpxchg_need_qs':
> update.c:(.text+0x348): undefined reference to `__bad_cmpxchg'
> arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function
> `rcu_read_unlock_trace_special':
> update.c:(.text+0x41c): undefined reference to `__bad_cmpxchg'
> arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function
> `trc_read_check_handler':
> update.c:(.text+0x4b0): undefined reference to `__bad_cmpxchg'
> arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function `trc_inspect_reader':
> update.c:(.text+0x1518): undefined reference to `__bad_cmpxchg'
> arm-linux-gnueabihf-ld: update.c:(.text+0x1548): undefined reference
> to `__bad_cmpxchg'
> arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4):
> more undefined references to `__bad_cmpxchg' follow
> make[3]: *** [/builds/linux/scripts/Makefile.vmlinux:34: vmlinux] Error 1

You get a reference to __bad_cmpxchg() when someone uses cmpxchg() on
a datatype that there are no CPU instructions to perform the atomic
compare-and-exchange.

As we support 8-bit, 16-bit and 32-bit, I would expect that we're now
seeing cmpxchg() being used on 64-bit values, which are unsupportable
on 32-bit Arm.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!

Re: arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4): more undefined references to `__bad_cmpxchg' follow

[Russell King (Oracle)]

On Thu, May 30, 2024 at 05:50:52PM +0530, Naresh Kamboju wrote:
> The arm builds failed on Linux next with gcc-13 and clang-18.
> 
> Config: arm imx_v6_v7_defconfig - failed
> 
> Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
> 
> Build log:
> -----
> arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function
> `rcu_trc_cmpxchg_need_qs':
> update.c:(.text+0x348): undefined reference to `__bad_cmpxchg'
> arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function
> `rcu_read_unlock_trace_special':
> update.c:(.text+0x41c): undefined reference to `__bad_cmpxchg'
> arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function
> `trc_read_check_handler':
> update.c:(.text+0x4b0): undefined reference to `__bad_cmpxchg'
> arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function `trc_inspect_reader':
> update.c:(.text+0x1518): undefined reference to `__bad_cmpxchg'
> arm-linux-gnueabihf-ld: update.c:(.text+0x1548): undefined reference
> to `__bad_cmpxchg'
> arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4):
> more undefined references to `__bad_cmpxchg' follow
> make[3]: *** [/builds/linux/scripts/Makefile.vmlinux:34: vmlinux] Error 1

You get a reference to __bad_cmpxchg() when someone uses cmpxchg() on
a datatype that there are no CPU instructions to perform the atomic
compare-and-exchange.

As we support 8-bit, 16-bit and 32-bit, I would expect that we're now
seeing cmpxchg() being used on 64-bit values, which are unsupportable
on 32-bit Arm.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

Re: arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4): more undefined references to `__bad_cmpxchg' follow

[Arnd Bergmann]

On Thu, May 30, 2024, at 14:26, Russell King (Oracle) wrote:
> On Thu, May 30, 2024 at 05:50:52PM +0530, Naresh Kamboju wrote:
>> The arm builds failed on Linux next with gcc-13 and clang-18.
>> 
>> Config: arm imx_v6_v7_defconfig - failed
>> 
>> Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
>> 
>> Build log:
>> -----
>> arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function
>> `rcu_trc_cmpxchg_need_qs':
>> update.c:(.text+0x348): undefined reference to `__bad_cmpxchg'
>> arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function
>> `rcu_read_unlock_trace_special':
>> update.c:(.text+0x41c): undefined reference to `__bad_cmpxchg'
>> arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function
>> `trc_read_check_handler':
>> update.c:(.text+0x4b0): undefined reference to `__bad_cmpxchg'
>> arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function `trc_inspect_reader':
>> update.c:(.text+0x1518): undefined reference to `__bad_cmpxchg'
>> arm-linux-gnueabihf-ld: update.c:(.text+0x1548): undefined reference
>> to `__bad_cmpxchg'
>> arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4):
>> more undefined references to `__bad_cmpxchg' follow
>> make[3]: *** [/builds/linux/scripts/Makefile.vmlinux:34: vmlinux] Error 1
>
> You get a reference to __bad_cmpxchg() when someone uses cmpxchg() on
> a datatype that there are no CPU instructions to perform the atomic
> compare-and-exchange.
>
> As we support 8-bit, 16-bit and 32-bit, I would expect that we're now
> seeing cmpxchg() being used on 64-bit values, which are unsupportable
> on 32-bit Arm.

A 64-bit cmpxchg() would fail on most 32-bit architectures,
other than armv6k+ and i686+. Since this one fails on
an armv6 (non-6k) build, it's probably the added 8-bit
cmpxchg() that Paul talked about using for RCU, though I
don't see that in linux-next here.

I htink we need to use the emulated cmpxchg8() in
__cmpxchg() for this case, just like we do on other
architectures that only have word size atomics.

      Arnd

Re: arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4): more undefined references to `__bad_cmpxchg' follow

[Arnd Bergmann]

On Thu, May 30, 2024, at 14:26, Russell King (Oracle) wrote:
> On Thu, May 30, 2024 at 05:50:52PM +0530, Naresh Kamboju wrote:
>> The arm builds failed on Linux next with gcc-13 and clang-18.
>> 
>> Config: arm imx_v6_v7_defconfig - failed
>> 
>> Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
>> 
>> Build log:
>> -----
>> arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function
>> `rcu_trc_cmpxchg_need_qs':
>> update.c:(.text+0x348): undefined reference to `__bad_cmpxchg'
>> arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function
>> `rcu_read_unlock_trace_special':
>> update.c:(.text+0x41c): undefined reference to `__bad_cmpxchg'
>> arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function
>> `trc_read_check_handler':
>> update.c:(.text+0x4b0): undefined reference to `__bad_cmpxchg'
>> arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function `trc_inspect_reader':
>> update.c:(.text+0x1518): undefined reference to `__bad_cmpxchg'
>> arm-linux-gnueabihf-ld: update.c:(.text+0x1548): undefined reference
>> to `__bad_cmpxchg'
>> arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4):
>> more undefined references to `__bad_cmpxchg' follow
>> make[3]: *** [/builds/linux/scripts/Makefile.vmlinux:34: vmlinux] Error 1
>
> You get a reference to __bad_cmpxchg() when someone uses cmpxchg() on
> a datatype that there are no CPU instructions to perform the atomic
> compare-and-exchange.
>
> As we support 8-bit, 16-bit and 32-bit, I would expect that we're now
> seeing cmpxchg() being used on 64-bit values, which are unsupportable
> on 32-bit Arm.

A 64-bit cmpxchg() would fail on most 32-bit architectures,
other than armv6k+ and i686+. Since this one fails on
an armv6 (non-6k) build, it's probably the added 8-bit
cmpxchg() that Paul talked about using for RCU, though I
don't see that in linux-next here.

I htink we need to use the emulated cmpxchg8() in
__cmpxchg() for this case, just like we do on other
architectures that only have word size atomics.

      Arnd

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
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Re: arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4): more undefined references to `__bad_cmpxchg' follow

[Paul E. McKenney]

On Thu, May 30, 2024 at 03:27:58PM +0200, Arnd Bergmann wrote:
> On Thu, May 30, 2024, at 14:26, Russell King (Oracle) wrote:
> > On Thu, May 30, 2024 at 05:50:52PM +0530, Naresh Kamboju wrote:
> >> The arm builds failed on Linux next with gcc-13 and clang-18.
> >> 
> >> Config: arm imx_v6_v7_defconfig - failed
> >> 
> >> Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
> >> 
> >> Build log:
> >> -----
> >> arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function
> >> `rcu_trc_cmpxchg_need_qs':
> >> update.c:(.text+0x348): undefined reference to `__bad_cmpxchg'
> >> arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function
> >> `rcu_read_unlock_trace_special':
> >> update.c:(.text+0x41c): undefined reference to `__bad_cmpxchg'
> >> arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function
> >> `trc_read_check_handler':
> >> update.c:(.text+0x4b0): undefined reference to `__bad_cmpxchg'
> >> arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function `trc_inspect_reader':
> >> update.c:(.text+0x1518): undefined reference to `__bad_cmpxchg'
> >> arm-linux-gnueabihf-ld: update.c:(.text+0x1548): undefined reference
> >> to `__bad_cmpxchg'
> >> arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4):
> >> more undefined references to `__bad_cmpxchg' follow
> >> make[3]: *** [/builds/linux/scripts/Makefile.vmlinux:34: vmlinux] Error 1
> >
> > You get a reference to __bad_cmpxchg() when someone uses cmpxchg() on
> > a datatype that there are no CPU instructions to perform the atomic
> > compare-and-exchange.
> >
> > As we support 8-bit, 16-bit and 32-bit, I would expect that we're now
> > seeing cmpxchg() being used on 64-bit values, which are unsupportable
> > on 32-bit Arm.
> 
> A 64-bit cmpxchg() would fail on most 32-bit architectures,
> other than armv6k+ and i686+. Since this one fails on
> an armv6 (non-6k) build, it's probably the added 8-bit
> cmpxchg() that Paul talked about using for RCU, though I
> don't see that in linux-next here.
> 
> I htink we need to use the emulated cmpxchg8() in
> __cmpxchg() for this case, just like we do on other
> architectures that only have word size atomics.

Thank you all for your testing and analysis!

I will fix this, and also pull the 8046f3005015 ("rcu-tasks: Remove
open-coded one-byte cmpxchg() emulation") commit out of my -next pile
in the meantime.

							Thanx, Paul

Re: arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4): more undefined references to `__bad_cmpxchg' follow

[Paul E. McKenney]

On Thu, May 30, 2024 at 03:27:58PM +0200, Arnd Bergmann wrote:
> On Thu, May 30, 2024, at 14:26, Russell King (Oracle) wrote:
> > On Thu, May 30, 2024 at 05:50:52PM +0530, Naresh Kamboju wrote:
> >> The arm builds failed on Linux next with gcc-13 and clang-18.
> >> 
> >> Config: arm imx_v6_v7_defconfig - failed
> >> 
> >> Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
> >> 
> >> Build log:
> >> -----
> >> arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function
> >> `rcu_trc_cmpxchg_need_qs':
> >> update.c:(.text+0x348): undefined reference to `__bad_cmpxchg'
> >> arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function
> >> `rcu_read_unlock_trace_special':
> >> update.c:(.text+0x41c): undefined reference to `__bad_cmpxchg'
> >> arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function
> >> `trc_read_check_handler':
> >> update.c:(.text+0x4b0): undefined reference to `__bad_cmpxchg'
> >> arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function `trc_inspect_reader':
> >> update.c:(.text+0x1518): undefined reference to `__bad_cmpxchg'
> >> arm-linux-gnueabihf-ld: update.c:(.text+0x1548): undefined reference
> >> to `__bad_cmpxchg'
> >> arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4):
> >> more undefined references to `__bad_cmpxchg' follow
> >> make[3]: *** [/builds/linux/scripts/Makefile.vmlinux:34: vmlinux] Error 1
> >
> > You get a reference to __bad_cmpxchg() when someone uses cmpxchg() on
> > a datatype that there are no CPU instructions to perform the atomic
> > compare-and-exchange.
> >
> > As we support 8-bit, 16-bit and 32-bit, I would expect that we're now
> > seeing cmpxchg() being used on 64-bit values, which are unsupportable
> > on 32-bit Arm.
> 
> A 64-bit cmpxchg() would fail on most 32-bit architectures,
> other than armv6k+ and i686+. Since this one fails on
> an armv6 (non-6k) build, it's probably the added 8-bit
> cmpxchg() that Paul talked about using for RCU, though I
> don't see that in linux-next here.
> 
> I htink we need to use the emulated cmpxchg8() in
> __cmpxchg() for this case, just like we do on other
> architectures that only have word size atomics.

Thank you all for your testing and analysis!

I will fix this, and also pull the 8046f3005015 ("rcu-tasks: Remove
open-coded one-byte cmpxchg() emulation") commit out of my -next pile
in the meantime.

							Thanx, Paul

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

Re: arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4): more undefined references to `__bad_cmpxchg' follow

[Paul E. McKenney]

On Thu, May 30, 2024 at 09:37:21AM -0700, Paul E. McKenney wrote:
> On Thu, May 30, 2024 at 03:27:58PM +0200, Arnd Bergmann wrote:
> > On Thu, May 30, 2024, at 14:26, Russell King (Oracle) wrote:
> > > On Thu, May 30, 2024 at 05:50:52PM +0530, Naresh Kamboju wrote:
> > >> The arm builds failed on Linux next with gcc-13 and clang-18.
> > >> 
> > >> Config: arm imx_v6_v7_defconfig - failed
> > >> 
> > >> Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
> > >> 
> > >> Build log:
> > >> -----
> > >> arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function
> > >> `rcu_trc_cmpxchg_need_qs':
> > >> update.c:(.text+0x348): undefined reference to `__bad_cmpxchg'
> > >> arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function
> > >> `rcu_read_unlock_trace_special':
> > >> update.c:(.text+0x41c): undefined reference to `__bad_cmpxchg'
> > >> arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function
> > >> `trc_read_check_handler':
> > >> update.c:(.text+0x4b0): undefined reference to `__bad_cmpxchg'
> > >> arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function `trc_inspect_reader':
> > >> update.c:(.text+0x1518): undefined reference to `__bad_cmpxchg'
> > >> arm-linux-gnueabihf-ld: update.c:(.text+0x1548): undefined reference
> > >> to `__bad_cmpxchg'
> > >> arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4):
> > >> more undefined references to `__bad_cmpxchg' follow
> > >> make[3]: *** [/builds/linux/scripts/Makefile.vmlinux:34: vmlinux] Error 1
> > >
> > > You get a reference to __bad_cmpxchg() when someone uses cmpxchg() on
> > > a datatype that there are no CPU instructions to perform the atomic
> > > compare-and-exchange.
> > >
> > > As we support 8-bit, 16-bit and 32-bit, I would expect that we're now
> > > seeing cmpxchg() being used on 64-bit values, which are unsupportable
> > > on 32-bit Arm.
> > 
> > A 64-bit cmpxchg() would fail on most 32-bit architectures,
> > other than armv6k+ and i686+. Since this one fails on
> > an armv6 (non-6k) build, it's probably the added 8-bit
> > cmpxchg() that Paul talked about using for RCU, though I
> > don't see that in linux-next here.
> > 
> > I htink we need to use the emulated cmpxchg8() in
> > __cmpxchg() for this case, just like we do on other
> > architectures that only have word size atomics.
> 
> Thank you all for your testing and analysis!
> 
> I will fix this, and also pull the 8046f3005015 ("rcu-tasks: Remove
> open-coded one-byte cmpxchg() emulation") commit out of my -next pile
> in the meantime.

And for an untested first attempt at a fix.

What did I mess up this time?  ;-)

							Thanx, Paul

------------------------------------------------------------------------

commit 6e43483dd111cf1be58b02a45d0ca729ca2634ba
Author: Paul E. McKenney <paulmck@kernel.org>
Date:   Thu May 30 10:11:31 2024 -0700

    ARM: Emulate one-byte cmpxchg
    
    Use the new cmpxchg_emu_u8() to emulate one-byte cmpxchg() on ARM systems
    with ARCH < ARMv6K.
    
    Reported-by: Mark Brown <broonie@kernel.org>
    Closes: https://lore.kernel.org/all/54798f68-48f7-4c65-9cba-47c0bf175143@sirena.org.uk/
    Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
    Closes: https://lore.kernel.org/all/CA+G9fYuZ+pf6p8AXMZWtdFtX-gbG8HMaBKp=XbxcdzA_QeLkxQ@mail.gmail.com/
    Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
    Cc: "Russell King (Oracle)" <rmk+kernel@armlinux.org.uk>
    Cc: Arnd Bergmann <arnd@arndb.de>
    Cc: Andrew Davis <afd@ti.com>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Linus Walleij <linus.walleij@linaro.org>
    Cc: Eric DeVolder <eric.devolder@oracle.com>
    Cc: Rob Herring <robh@kernel.org>
    Cc: <linux-arm-kernel@lists.infradead.org>

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index ee5115252aac4..a867a7d967aa5 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -34,6 +34,7 @@ config ARM
 	select ARCH_MIGHT_HAVE_PC_PARPORT
 	select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX
 	select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT if CPU_V7
+	select ARCH_NEED_CMPXCHG_1_EMU if CPU_V6
 	select ARCH_SUPPORTS_ATOMIC_RMW
 	select ARCH_SUPPORTS_CFI_CLANG
 	select ARCH_SUPPORTS_HUGETLBFS if ARM_LPAE
diff --git a/arch/arm/include/asm/cmpxchg.h b/arch/arm/include/asm/cmpxchg.h
index 44667bdb4707a..fd9b99f4dca46 100644
--- a/arch/arm/include/asm/cmpxchg.h
+++ b/arch/arm/include/asm/cmpxchg.h
@@ -162,7 +162,11 @@ static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
 	prefetchw((const void *)ptr);
 
 	switch (size) {
-#ifndef CONFIG_CPU_V6	/* min ARCH >= ARMv6K */
+#ifdef CONFIG_CPU_V6	/* min ARCH >= ARMv6K */
+	case 1:
+		oldval = cmpxchg_emu_u8((volatile u8 *)ptr, old, new);
+		break;
+#else
 	case 1:
 		do {
 			asm volatile("@ __cmpxchg1\n"

Re: arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4): more undefined references to `__bad_cmpxchg' follow

[Paul E. McKenney]

On Thu, May 30, 2024 at 09:37:21AM -0700, Paul E. McKenney wrote:
> On Thu, May 30, 2024 at 03:27:58PM +0200, Arnd Bergmann wrote:
> > On Thu, May 30, 2024, at 14:26, Russell King (Oracle) wrote:
> > > On Thu, May 30, 2024 at 05:50:52PM +0530, Naresh Kamboju wrote:
> > >> The arm builds failed on Linux next with gcc-13 and clang-18.
> > >> 
> > >> Config: arm imx_v6_v7_defconfig - failed
> > >> 
> > >> Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
> > >> 
> > >> Build log:
> > >> -----
> > >> arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function
> > >> `rcu_trc_cmpxchg_need_qs':
> > >> update.c:(.text+0x348): undefined reference to `__bad_cmpxchg'
> > >> arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function
> > >> `rcu_read_unlock_trace_special':
> > >> update.c:(.text+0x41c): undefined reference to `__bad_cmpxchg'
> > >> arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function
> > >> `trc_read_check_handler':
> > >> update.c:(.text+0x4b0): undefined reference to `__bad_cmpxchg'
> > >> arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function `trc_inspect_reader':
> > >> update.c:(.text+0x1518): undefined reference to `__bad_cmpxchg'
> > >> arm-linux-gnueabihf-ld: update.c:(.text+0x1548): undefined reference
> > >> to `__bad_cmpxchg'
> > >> arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4):
> > >> more undefined references to `__bad_cmpxchg' follow
> > >> make[3]: *** [/builds/linux/scripts/Makefile.vmlinux:34: vmlinux] Error 1
> > >
> > > You get a reference to __bad_cmpxchg() when someone uses cmpxchg() on
> > > a datatype that there are no CPU instructions to perform the atomic
> > > compare-and-exchange.
> > >
> > > As we support 8-bit, 16-bit and 32-bit, I would expect that we're now
> > > seeing cmpxchg() being used on 64-bit values, which are unsupportable
> > > on 32-bit Arm.
> > 
> > A 64-bit cmpxchg() would fail on most 32-bit architectures,
> > other than armv6k+ and i686+. Since this one fails on
> > an armv6 (non-6k) build, it's probably the added 8-bit
> > cmpxchg() that Paul talked about using for RCU, though I
> > don't see that in linux-next here.
> > 
> > I htink we need to use the emulated cmpxchg8() in
> > __cmpxchg() for this case, just like we do on other
> > architectures that only have word size atomics.
> 
> Thank you all for your testing and analysis!
> 
> I will fix this, and also pull the 8046f3005015 ("rcu-tasks: Remove
> open-coded one-byte cmpxchg() emulation") commit out of my -next pile
> in the meantime.

And for an untested first attempt at a fix.

What did I mess up this time?  ;-)

							Thanx, Paul

------------------------------------------------------------------------

commit 6e43483dd111cf1be58b02a45d0ca729ca2634ba
Author: Paul E. McKenney <paulmck@kernel.org>
Date:   Thu May 30 10:11:31 2024 -0700

    ARM: Emulate one-byte cmpxchg
    
    Use the new cmpxchg_emu_u8() to emulate one-byte cmpxchg() on ARM systems
    with ARCH < ARMv6K.
    
    Reported-by: Mark Brown <broonie@kernel.org>
    Closes: https://lore.kernel.org/all/54798f68-48f7-4c65-9cba-47c0bf175143@sirena.org.uk/
    Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
    Closes: https://lore.kernel.org/all/CA+G9fYuZ+pf6p8AXMZWtdFtX-gbG8HMaBKp=XbxcdzA_QeLkxQ@mail.gmail.com/
    Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
    Cc: "Russell King (Oracle)" <rmk+kernel@armlinux.org.uk>
    Cc: Arnd Bergmann <arnd@arndb.de>
    Cc: Andrew Davis <afd@ti.com>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Linus Walleij <linus.walleij@linaro.org>
    Cc: Eric DeVolder <eric.devolder@oracle.com>
    Cc: Rob Herring <robh@kernel.org>
    Cc: <linux-arm-kernel@lists.infradead.org>

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index ee5115252aac4..a867a7d967aa5 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -34,6 +34,7 @@ config ARM
 	select ARCH_MIGHT_HAVE_PC_PARPORT
 	select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX
 	select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT if CPU_V7
+	select ARCH_NEED_CMPXCHG_1_EMU if CPU_V6
 	select ARCH_SUPPORTS_ATOMIC_RMW
 	select ARCH_SUPPORTS_CFI_CLANG
 	select ARCH_SUPPORTS_HUGETLBFS if ARM_LPAE
diff --git a/arch/arm/include/asm/cmpxchg.h b/arch/arm/include/asm/cmpxchg.h
index 44667bdb4707a..fd9b99f4dca46 100644
--- a/arch/arm/include/asm/cmpxchg.h
+++ b/arch/arm/include/asm/cmpxchg.h
@@ -162,7 +162,11 @@ static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
 	prefetchw((const void *)ptr);
 
 	switch (size) {
-#ifndef CONFIG_CPU_V6	/* min ARCH >= ARMv6K */
+#ifdef CONFIG_CPU_V6	/* min ARCH >= ARMv6K */
+	case 1:
+		oldval = cmpxchg_emu_u8((volatile u8 *)ptr, old, new);
+		break;
+#else
 	case 1:
 		do {
 			asm volatile("@ __cmpxchg1\n"

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Re: arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4): more undefined references to `__bad_cmpxchg' follow

[Arnd Bergmann]

On Thu, May 30, 2024, at 19:24, Paul E. McKenney wrote:
> On Thu, May 30, 2024 at 09:37:21AM -0700, Paul E. McKenney wrote:
>> On Thu, May 30, 2024 at 03:27:58PM +0200, Arnd Bergmann wrote:

> And for an untested first attempt at a fix.
>
> What did I mess up this time?  ;-)
>

I think only the comment:

> 
>  	switch (size) {
> -#ifndef CONFIG_CPU_V6	/* min ARCH >= ARMv6K */
> +#ifdef CONFIG_CPU_V6	/* min ARCH >= ARMv6K */
> +	case 1:
> +		oldval = cmpxchg_emu_u8((volatile u8 *)ptr, old, new);
> +		break;
> +#else

"min ARCH >= ARMv6K" now applies to the #else side, while the
#if side is the early ARMv6 (pre-v6K).

     Arnd

Re: arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4): more undefined references to `__bad_cmpxchg' follow

[Arnd Bergmann]

On Thu, May 30, 2024, at 19:24, Paul E. McKenney wrote:
> On Thu, May 30, 2024 at 09:37:21AM -0700, Paul E. McKenney wrote:
>> On Thu, May 30, 2024 at 03:27:58PM +0200, Arnd Bergmann wrote:

> And for an untested first attempt at a fix.
>
> What did I mess up this time?  ;-)
>

I think only the comment:

> 
>  	switch (size) {
> -#ifndef CONFIG_CPU_V6	/* min ARCH >= ARMv6K */
> +#ifdef CONFIG_CPU_V6	/* min ARCH >= ARMv6K */
> +	case 1:
> +		oldval = cmpxchg_emu_u8((volatile u8 *)ptr, old, new);
> +		break;
> +#else

"min ARCH >= ARMv6K" now applies to the #else side, while the
#if side is the early ARMv6 (pre-v6K).

     Arnd

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Re: arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4): more undefined references to `__bad_cmpxchg' follow

[Paul E. McKenney]

On Thu, May 30, 2024 at 08:05:50PM +0200, Arnd Bergmann wrote:
> On Thu, May 30, 2024, at 19:24, Paul E. McKenney wrote:
> > On Thu, May 30, 2024 at 09:37:21AM -0700, Paul E. McKenney wrote:
> >> On Thu, May 30, 2024 at 03:27:58PM +0200, Arnd Bergmann wrote:
> 
> > And for an untested first attempt at a fix.
> >
> > What did I mess up this time?  ;-)
> >
> 
> I think only the comment:
> 
> > 
> >  	switch (size) {
> > -#ifndef CONFIG_CPU_V6	/* min ARCH >= ARMv6K */
> > +#ifdef CONFIG_CPU_V6	/* min ARCH >= ARMv6K */
> > +	case 1:
> > +		oldval = cmpxchg_emu_u8((volatile u8 *)ptr, old, new);
> > +		break;
> > +#else
> 
> "min ARCH >= ARMv6K" now applies to the #else side, while the
> #if side is the early ARMv6 (pre-v6K).

Good catch!

I plan to fold the following into the original with attribution.

							Thanx, Paul

------------------------------------------------------------------------

diff --git a/arch/arm/include/asm/cmpxchg.h b/arch/arm/include/asm/cmpxchg.h
index fd9b99f4dca46..34674a4118755 100644
--- a/arch/arm/include/asm/cmpxchg.h
+++ b/arch/arm/include/asm/cmpxchg.h
@@ -162,11 +162,11 @@ static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
 	prefetchw((const void *)ptr);
 
 	switch (size) {
-#ifdef CONFIG_CPU_V6	/* min ARCH >= ARMv6K */
+#ifdef CONFIG_CPU_V6	/* min ARCH < ARMv6K */
 	case 1:
 		oldval = cmpxchg_emu_u8((volatile u8 *)ptr, old, new);
 		break;
-#else
+#else /* min ARCH >= ARMv6K */
 	case 1:
 		do {
 			asm volatile("@ __cmpxchg1\n"

Re: arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4): more undefined references to `__bad_cmpxchg' follow

[Paul E. McKenney]

On Thu, May 30, 2024 at 08:05:50PM +0200, Arnd Bergmann wrote:
> On Thu, May 30, 2024, at 19:24, Paul E. McKenney wrote:
> > On Thu, May 30, 2024 at 09:37:21AM -0700, Paul E. McKenney wrote:
> >> On Thu, May 30, 2024 at 03:27:58PM +0200, Arnd Bergmann wrote:
> 
> > And for an untested first attempt at a fix.
> >
> > What did I mess up this time?  ;-)
> >
> 
> I think only the comment:
> 
> > 
> >  	switch (size) {
> > -#ifndef CONFIG_CPU_V6	/* min ARCH >= ARMv6K */
> > +#ifdef CONFIG_CPU_V6	/* min ARCH >= ARMv6K */
> > +	case 1:
> > +		oldval = cmpxchg_emu_u8((volatile u8 *)ptr, old, new);
> > +		break;
> > +#else
> 
> "min ARCH >= ARMv6K" now applies to the #else side, while the
> #if side is the early ARMv6 (pre-v6K).

Good catch!

I plan to fold the following into the original with attribution.

							Thanx, Paul

------------------------------------------------------------------------

diff --git a/arch/arm/include/asm/cmpxchg.h b/arch/arm/include/asm/cmpxchg.h
index fd9b99f4dca46..34674a4118755 100644
--- a/arch/arm/include/asm/cmpxchg.h
+++ b/arch/arm/include/asm/cmpxchg.h
@@ -162,11 +162,11 @@ static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
 	prefetchw((const void *)ptr);
 
 	switch (size) {
-#ifdef CONFIG_CPU_V6	/* min ARCH >= ARMv6K */
+#ifdef CONFIG_CPU_V6	/* min ARCH < ARMv6K */
 	case 1:
 		oldval = cmpxchg_emu_u8((volatile u8 *)ptr, old, new);
 		break;
-#else
+#else /* min ARCH >= ARMv6K */
 	case 1:
 		do {
 			asm volatile("@ __cmpxchg1\n"

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Re: arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4): more undefined references to `__bad_cmpxchg' follow

[Nathan Chancellor]

On Thu, May 30, 2024 at 10:24:05AM -0700, Paul E. McKenney wrote:
> And for an untested first attempt at a fix.
> 
> What did I mess up this time?  ;-)

An include for cmpxchg-emu.h ;)

  In file included from arch/arm/include/asm/atomic.h:16,
                   from include/linux/atomic.h:7,
                   from include/asm-generic/bitops/lock.h:5,
                   from arch/arm/include/asm/bitops.h:245,
                   from include/linux/bitops.h:63,
                   from include/linux/log2.h:12,
                   from kernel/bounds.c:13:
  arch/arm/include/asm/cmpxchg.h: In function '__cmpxchg':
  arch/arm/include/asm/cmpxchg.h:167:26: error: implicit declaration of function 'cmpxchg_emu_u8' [-Werror=implicit-function-declaration]
    167 |                 oldval = cmpxchg_emu_u8((volatile u8 *)ptr, old, new);
        |                          ^~~~~~~~~~~~~~
  cc1: some warnings being treated as errors

> 							Thanx, Paul
> 
> ------------------------------------------------------------------------
> 
> commit 6e43483dd111cf1be58b02a45d0ca729ca2634ba
> Author: Paul E. McKenney <paulmck@kernel.org>
> Date:   Thu May 30 10:11:31 2024 -0700
> 
>     ARM: Emulate one-byte cmpxchg
>     
>     Use the new cmpxchg_emu_u8() to emulate one-byte cmpxchg() on ARM systems
>     with ARCH < ARMv6K.
>     
>     Reported-by: Mark Brown <broonie@kernel.org>
>     Closes: https://lore.kernel.org/all/54798f68-48f7-4c65-9cba-47c0bf175143@sirena.org.uk/
>     Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
>     Closes: https://lore.kernel.org/all/CA+G9fYuZ+pf6p8AXMZWtdFtX-gbG8HMaBKp=XbxcdzA_QeLkxQ@mail.gmail.com/
>     Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
>     Cc: "Russell King (Oracle)" <rmk+kernel@armlinux.org.uk>
>     Cc: Arnd Bergmann <arnd@arndb.de>
>     Cc: Andrew Davis <afd@ti.com>
>     Cc: Andrew Morton <akpm@linux-foundation.org>
>     Cc: Linus Walleij <linus.walleij@linaro.org>
>     Cc: Eric DeVolder <eric.devolder@oracle.com>
>     Cc: Rob Herring <robh@kernel.org>
>     Cc: <linux-arm-kernel@lists.infradead.org>
> 
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index ee5115252aac4..a867a7d967aa5 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -34,6 +34,7 @@ config ARM
>  	select ARCH_MIGHT_HAVE_PC_PARPORT
>  	select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX
>  	select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT if CPU_V7
> +	select ARCH_NEED_CMPXCHG_1_EMU if CPU_V6
>  	select ARCH_SUPPORTS_ATOMIC_RMW
>  	select ARCH_SUPPORTS_CFI_CLANG
>  	select ARCH_SUPPORTS_HUGETLBFS if ARM_LPAE
> diff --git a/arch/arm/include/asm/cmpxchg.h b/arch/arm/include/asm/cmpxchg.h
> index 44667bdb4707a..fd9b99f4dca46 100644
> --- a/arch/arm/include/asm/cmpxchg.h
> +++ b/arch/arm/include/asm/cmpxchg.h
> @@ -162,7 +162,11 @@ static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
>  	prefetchw((const void *)ptr);
>  
>  	switch (size) {
> -#ifndef CONFIG_CPU_V6	/* min ARCH >= ARMv6K */
> +#ifdef CONFIG_CPU_V6	/* min ARCH >= ARMv6K */
> +	case 1:
> +		oldval = cmpxchg_emu_u8((volatile u8 *)ptr, old, new);
> +		break;
> +#else
>  	case 1:
>  		do {
>  			asm volatile("@ __cmpxchg1\n"
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

Re: arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4): more undefined references to `__bad_cmpxchg' follow

[Nathan Chancellor]

On Thu, May 30, 2024 at 10:24:05AM -0700, Paul E. McKenney wrote:
> And for an untested first attempt at a fix.
> 
> What did I mess up this time?  ;-)

An include for cmpxchg-emu.h ;)

  In file included from arch/arm/include/asm/atomic.h:16,
                   from include/linux/atomic.h:7,
                   from include/asm-generic/bitops/lock.h:5,
                   from arch/arm/include/asm/bitops.h:245,
                   from include/linux/bitops.h:63,
                   from include/linux/log2.h:12,
                   from kernel/bounds.c:13:
  arch/arm/include/asm/cmpxchg.h: In function '__cmpxchg':
  arch/arm/include/asm/cmpxchg.h:167:26: error: implicit declaration of function 'cmpxchg_emu_u8' [-Werror=implicit-function-declaration]
    167 |                 oldval = cmpxchg_emu_u8((volatile u8 *)ptr, old, new);
        |                          ^~~~~~~~~~~~~~
  cc1: some warnings being treated as errors

> 							Thanx, Paul
> 
> ------------------------------------------------------------------------
> 
> commit 6e43483dd111cf1be58b02a45d0ca729ca2634ba
> Author: Paul E. McKenney <paulmck@kernel.org>
> Date:   Thu May 30 10:11:31 2024 -0700
> 
>     ARM: Emulate one-byte cmpxchg
>     
>     Use the new cmpxchg_emu_u8() to emulate one-byte cmpxchg() on ARM systems
>     with ARCH < ARMv6K.
>     
>     Reported-by: Mark Brown <broonie@kernel.org>
>     Closes: https://lore.kernel.org/all/54798f68-48f7-4c65-9cba-47c0bf175143@sirena.org.uk/
>     Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
>     Closes: https://lore.kernel.org/all/CA+G9fYuZ+pf6p8AXMZWtdFtX-gbG8HMaBKp=XbxcdzA_QeLkxQ@mail.gmail.com/
>     Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
>     Cc: "Russell King (Oracle)" <rmk+kernel@armlinux.org.uk>
>     Cc: Arnd Bergmann <arnd@arndb.de>
>     Cc: Andrew Davis <afd@ti.com>
>     Cc: Andrew Morton <akpm@linux-foundation.org>
>     Cc: Linus Walleij <linus.walleij@linaro.org>
>     Cc: Eric DeVolder <eric.devolder@oracle.com>
>     Cc: Rob Herring <robh@kernel.org>
>     Cc: <linux-arm-kernel@lists.infradead.org>
> 
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index ee5115252aac4..a867a7d967aa5 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -34,6 +34,7 @@ config ARM
>  	select ARCH_MIGHT_HAVE_PC_PARPORT
>  	select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX
>  	select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT if CPU_V7
> +	select ARCH_NEED_CMPXCHG_1_EMU if CPU_V6
>  	select ARCH_SUPPORTS_ATOMIC_RMW
>  	select ARCH_SUPPORTS_CFI_CLANG
>  	select ARCH_SUPPORTS_HUGETLBFS if ARM_LPAE
> diff --git a/arch/arm/include/asm/cmpxchg.h b/arch/arm/include/asm/cmpxchg.h
> index 44667bdb4707a..fd9b99f4dca46 100644
> --- a/arch/arm/include/asm/cmpxchg.h
> +++ b/arch/arm/include/asm/cmpxchg.h
> @@ -162,7 +162,11 @@ static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
>  	prefetchw((const void *)ptr);
>  
>  	switch (size) {
> -#ifndef CONFIG_CPU_V6	/* min ARCH >= ARMv6K */
> +#ifdef CONFIG_CPU_V6	/* min ARCH >= ARMv6K */
> +	case 1:
> +		oldval = cmpxchg_emu_u8((volatile u8 *)ptr, old, new);
> +		break;
> +#else
>  	case 1:
>  		do {
>  			asm volatile("@ __cmpxchg1\n"
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

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Re: arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4): more undefined references to `__bad_cmpxchg' follow

[Paul E. McKenney]

On Thu, May 30, 2024 at 02:52:48PM -0700, Nathan Chancellor wrote:
> On Thu, May 30, 2024 at 10:24:05AM -0700, Paul E. McKenney wrote:
> > And for an untested first attempt at a fix.
> > 
> > What did I mess up this time?  ;-)
> 
> An include for cmpxchg-emu.h ;)
> 
>   In file included from arch/arm/include/asm/atomic.h:16,
>                    from include/linux/atomic.h:7,
>                    from include/asm-generic/bitops/lock.h:5,
>                    from arch/arm/include/asm/bitops.h:245,
>                    from include/linux/bitops.h:63,
>                    from include/linux/log2.h:12,
>                    from kernel/bounds.c:13:
>   arch/arm/include/asm/cmpxchg.h: In function '__cmpxchg':
>   arch/arm/include/asm/cmpxchg.h:167:26: error: implicit declaration of function 'cmpxchg_emu_u8' [-Werror=implicit-function-declaration]
>     167 |                 oldval = cmpxchg_emu_u8((volatile u8 *)ptr, old, new);
>         |                          ^~~~~~~~~~~~~~
>   cc1: some warnings being treated as errors

Good catch, and thank you for testing this!  Does the updated version
shown below do better?

							Thanx, Paul

------------------------------------------------------------------------

commit 74e3470afacaa9d2f37db4773a5fef887ac4ef56
Author: Paul E. McKenney <paulmck@kernel.org>
Date:   Thu May 30 10:11:31 2024 -0700

    ARM: Emulate one-byte cmpxchg
    
    Use the new cmpxchg_emu_u8() to emulate one-byte cmpxchg() on ARM systems
    with ARCH < ARMv6K.
    
    [ paulmck: Apply Arnd Bergmann and Nathan Chancellor feedback. ]
    
    Reported-by: Mark Brown <broonie@kernel.org>
    Closes: https://lore.kernel.org/all/54798f68-48f7-4c65-9cba-47c0bf175143@sirena.org.uk/
    Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
    Closes: https://lore.kernel.org/all/CA+G9fYuZ+pf6p8AXMZWtdFtX-gbG8HMaBKp=XbxcdzA_QeLkxQ@mail.gmail.com/
    Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
    Cc: "Russell King (Oracle)" <rmk+kernel@armlinux.org.uk>
    Cc: Arnd Bergmann <arnd@arndb.de>
    Cc: Andrew Davis <afd@ti.com>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Linus Walleij <linus.walleij@linaro.org>
    Cc: Eric DeVolder <eric.devolder@oracle.com>
    Cc: Rob Herring <robh@kernel.org>
    Cc: <linux-arm-kernel@lists.infradead.org>

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index ee5115252aac4..a867a7d967aa5 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -34,6 +34,7 @@ config ARM
 	select ARCH_MIGHT_HAVE_PC_PARPORT
 	select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX
 	select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT if CPU_V7
+	select ARCH_NEED_CMPXCHG_1_EMU if CPU_V6
 	select ARCH_SUPPORTS_ATOMIC_RMW
 	select ARCH_SUPPORTS_CFI_CLANG
 	select ARCH_SUPPORTS_HUGETLBFS if ARM_LPAE
diff --git a/arch/arm/include/asm/cmpxchg.h b/arch/arm/include/asm/cmpxchg.h
index 44667bdb4707a..a428e06fe94ee 100644
--- a/arch/arm/include/asm/cmpxchg.h
+++ b/arch/arm/include/asm/cmpxchg.h
@@ -5,6 +5,7 @@
 #include <linux/irqflags.h>
 #include <linux/prefetch.h>
 #include <asm/barrier.h>
+#include <linux/cmpxchg-emu.h>
 
 #if defined(CONFIG_CPU_SA1100) || defined(CONFIG_CPU_SA110)
 /*
@@ -162,7 +163,11 @@ static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
 	prefetchw((const void *)ptr);
 
 	switch (size) {
-#ifndef CONFIG_CPU_V6	/* min ARCH >= ARMv6K */
+#ifdef CONFIG_CPU_V6	/* min ARCH < ARMv6K */
+	case 1:
+		oldval = cmpxchg_emu_u8((volatile u8 *)ptr, old, new);
+		break;
+#else /* min ARCH >= ARMv6K */
 	case 1:
 		do {
 			asm volatile("@ __cmpxchg1\n"

Re: arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4): more undefined references to `__bad_cmpxchg' follow

[Paul E. McKenney]

On Thu, May 30, 2024 at 02:52:48PM -0700, Nathan Chancellor wrote:
> On Thu, May 30, 2024 at 10:24:05AM -0700, Paul E. McKenney wrote:
> > And for an untested first attempt at a fix.
> > 
> > What did I mess up this time?  ;-)
> 
> An include for cmpxchg-emu.h ;)
> 
>   In file included from arch/arm/include/asm/atomic.h:16,
>                    from include/linux/atomic.h:7,
>                    from include/asm-generic/bitops/lock.h:5,
>                    from arch/arm/include/asm/bitops.h:245,
>                    from include/linux/bitops.h:63,
>                    from include/linux/log2.h:12,
>                    from kernel/bounds.c:13:
>   arch/arm/include/asm/cmpxchg.h: In function '__cmpxchg':
>   arch/arm/include/asm/cmpxchg.h:167:26: error: implicit declaration of function 'cmpxchg_emu_u8' [-Werror=implicit-function-declaration]
>     167 |                 oldval = cmpxchg_emu_u8((volatile u8 *)ptr, old, new);
>         |                          ^~~~~~~~~~~~~~
>   cc1: some warnings being treated as errors

Good catch, and thank you for testing this!  Does the updated version
shown below do better?

							Thanx, Paul

------------------------------------------------------------------------

commit 74e3470afacaa9d2f37db4773a5fef887ac4ef56
Author: Paul E. McKenney <paulmck@kernel.org>
Date:   Thu May 30 10:11:31 2024 -0700

    ARM: Emulate one-byte cmpxchg
    
    Use the new cmpxchg_emu_u8() to emulate one-byte cmpxchg() on ARM systems
    with ARCH < ARMv6K.
    
    [ paulmck: Apply Arnd Bergmann and Nathan Chancellor feedback. ]
    
    Reported-by: Mark Brown <broonie@kernel.org>
    Closes: https://lore.kernel.org/all/54798f68-48f7-4c65-9cba-47c0bf175143@sirena.org.uk/
    Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
    Closes: https://lore.kernel.org/all/CA+G9fYuZ+pf6p8AXMZWtdFtX-gbG8HMaBKp=XbxcdzA_QeLkxQ@mail.gmail.com/
    Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
    Cc: "Russell King (Oracle)" <rmk+kernel@armlinux.org.uk>
    Cc: Arnd Bergmann <arnd@arndb.de>
    Cc: Andrew Davis <afd@ti.com>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Linus Walleij <linus.walleij@linaro.org>
    Cc: Eric DeVolder <eric.devolder@oracle.com>
    Cc: Rob Herring <robh@kernel.org>
    Cc: <linux-arm-kernel@lists.infradead.org>

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index ee5115252aac4..a867a7d967aa5 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -34,6 +34,7 @@ config ARM
 	select ARCH_MIGHT_HAVE_PC_PARPORT
 	select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX
 	select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT if CPU_V7
+	select ARCH_NEED_CMPXCHG_1_EMU if CPU_V6
 	select ARCH_SUPPORTS_ATOMIC_RMW
 	select ARCH_SUPPORTS_CFI_CLANG
 	select ARCH_SUPPORTS_HUGETLBFS if ARM_LPAE
diff --git a/arch/arm/include/asm/cmpxchg.h b/arch/arm/include/asm/cmpxchg.h
index 44667bdb4707a..a428e06fe94ee 100644
--- a/arch/arm/include/asm/cmpxchg.h
+++ b/arch/arm/include/asm/cmpxchg.h
@@ -5,6 +5,7 @@
 #include <linux/irqflags.h>
 #include <linux/prefetch.h>
 #include <asm/barrier.h>
+#include <linux/cmpxchg-emu.h>
 
 #if defined(CONFIG_CPU_SA1100) || defined(CONFIG_CPU_SA110)
 /*
@@ -162,7 +163,11 @@ static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
 	prefetchw((const void *)ptr);
 
 	switch (size) {
-#ifndef CONFIG_CPU_V6	/* min ARCH >= ARMv6K */
+#ifdef CONFIG_CPU_V6	/* min ARCH < ARMv6K */
+	case 1:
+		oldval = cmpxchg_emu_u8((volatile u8 *)ptr, old, new);
+		break;
+#else /* min ARCH >= ARMv6K */
 	case 1:
 		do {
 			asm volatile("@ __cmpxchg1\n"

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Re: arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4): more undefined references to `__bad_cmpxchg' follow

[Nathan Chancellor]

On Thu, May 30, 2024 at 03:05:21PM -0700, Paul E. McKenney wrote:
> On Thu, May 30, 2024 at 02:52:48PM -0700, Nathan Chancellor wrote:
> > On Thu, May 30, 2024 at 10:24:05AM -0700, Paul E. McKenney wrote:
> > > And for an untested first attempt at a fix.
> > > 
> > > What did I mess up this time?  ;-)
> > 
> > An include for cmpxchg-emu.h ;)
> > 
> >   In file included from arch/arm/include/asm/atomic.h:16,
> >                    from include/linux/atomic.h:7,
> >                    from include/asm-generic/bitops/lock.h:5,
> >                    from arch/arm/include/asm/bitops.h:245,
> >                    from include/linux/bitops.h:63,
> >                    from include/linux/log2.h:12,
> >                    from kernel/bounds.c:13:
> >   arch/arm/include/asm/cmpxchg.h: In function '__cmpxchg':
> >   arch/arm/include/asm/cmpxchg.h:167:26: error: implicit declaration of function 'cmpxchg_emu_u8' [-Werror=implicit-function-declaration]
> >     167 |                 oldval = cmpxchg_emu_u8((volatile u8 *)ptr, old, new);
> >         |                          ^~~~~~~~~~~~~~
> >   cc1: some warnings being treated as errors
> 
> Good catch, and thank you for testing this!  Does the updated version
> shown below do better?

Yes, that matches what I tested locally before I replied initially.

Thanks for the quick fix!

Cheers,
Nathan

> 							Thanx, Paul
> 
> ------------------------------------------------------------------------
> 
> commit 74e3470afacaa9d2f37db4773a5fef887ac4ef56
> Author: Paul E. McKenney <paulmck@kernel.org>
> Date:   Thu May 30 10:11:31 2024 -0700
> 
>     ARM: Emulate one-byte cmpxchg
>     
>     Use the new cmpxchg_emu_u8() to emulate one-byte cmpxchg() on ARM systems
>     with ARCH < ARMv6K.
>     
>     [ paulmck: Apply Arnd Bergmann and Nathan Chancellor feedback. ]
>     
>     Reported-by: Mark Brown <broonie@kernel.org>
>     Closes: https://lore.kernel.org/all/54798f68-48f7-4c65-9cba-47c0bf175143@sirena.org.uk/
>     Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
>     Closes: https://lore.kernel.org/all/CA+G9fYuZ+pf6p8AXMZWtdFtX-gbG8HMaBKp=XbxcdzA_QeLkxQ@mail.gmail.com/
>     Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
>     Cc: "Russell King (Oracle)" <rmk+kernel@armlinux.org.uk>
>     Cc: Arnd Bergmann <arnd@arndb.de>
>     Cc: Andrew Davis <afd@ti.com>
>     Cc: Andrew Morton <akpm@linux-foundation.org>
>     Cc: Linus Walleij <linus.walleij@linaro.org>
>     Cc: Eric DeVolder <eric.devolder@oracle.com>
>     Cc: Rob Herring <robh@kernel.org>
>     Cc: <linux-arm-kernel@lists.infradead.org>
> 
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index ee5115252aac4..a867a7d967aa5 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -34,6 +34,7 @@ config ARM
>  	select ARCH_MIGHT_HAVE_PC_PARPORT
>  	select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX
>  	select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT if CPU_V7
> +	select ARCH_NEED_CMPXCHG_1_EMU if CPU_V6
>  	select ARCH_SUPPORTS_ATOMIC_RMW
>  	select ARCH_SUPPORTS_CFI_CLANG
>  	select ARCH_SUPPORTS_HUGETLBFS if ARM_LPAE
> diff --git a/arch/arm/include/asm/cmpxchg.h b/arch/arm/include/asm/cmpxchg.h
> index 44667bdb4707a..a428e06fe94ee 100644
> --- a/arch/arm/include/asm/cmpxchg.h
> +++ b/arch/arm/include/asm/cmpxchg.h
> @@ -5,6 +5,7 @@
>  #include <linux/irqflags.h>
>  #include <linux/prefetch.h>
>  #include <asm/barrier.h>
> +#include <linux/cmpxchg-emu.h>
>  
>  #if defined(CONFIG_CPU_SA1100) || defined(CONFIG_CPU_SA110)
>  /*
> @@ -162,7 +163,11 @@ static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
>  	prefetchw((const void *)ptr);
>  
>  	switch (size) {
> -#ifndef CONFIG_CPU_V6	/* min ARCH >= ARMv6K */
> +#ifdef CONFIG_CPU_V6	/* min ARCH < ARMv6K */
> +	case 1:
> +		oldval = cmpxchg_emu_u8((volatile u8 *)ptr, old, new);
> +		break;
> +#else /* min ARCH >= ARMv6K */
>  	case 1:
>  		do {
>  			asm volatile("@ __cmpxchg1\n"

Re: arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4): more undefined references to `__bad_cmpxchg' follow

[Nathan Chancellor]

On Thu, May 30, 2024 at 03:05:21PM -0700, Paul E. McKenney wrote:
> On Thu, May 30, 2024 at 02:52:48PM -0700, Nathan Chancellor wrote:
> > On Thu, May 30, 2024 at 10:24:05AM -0700, Paul E. McKenney wrote:
> > > And for an untested first attempt at a fix.
> > > 
> > > What did I mess up this time?  ;-)
> > 
> > An include for cmpxchg-emu.h ;)
> > 
> >   In file included from arch/arm/include/asm/atomic.h:16,
> >                    from include/linux/atomic.h:7,
> >                    from include/asm-generic/bitops/lock.h:5,
> >                    from arch/arm/include/asm/bitops.h:245,
> >                    from include/linux/bitops.h:63,
> >                    from include/linux/log2.h:12,
> >                    from kernel/bounds.c:13:
> >   arch/arm/include/asm/cmpxchg.h: In function '__cmpxchg':
> >   arch/arm/include/asm/cmpxchg.h:167:26: error: implicit declaration of function 'cmpxchg_emu_u8' [-Werror=implicit-function-declaration]
> >     167 |                 oldval = cmpxchg_emu_u8((volatile u8 *)ptr, old, new);
> >         |                          ^~~~~~~~~~~~~~
> >   cc1: some warnings being treated as errors
> 
> Good catch, and thank you for testing this!  Does the updated version
> shown below do better?

Yes, that matches what I tested locally before I replied initially.

Thanks for the quick fix!

Cheers,
Nathan

> 							Thanx, Paul
> 
> ------------------------------------------------------------------------
> 
> commit 74e3470afacaa9d2f37db4773a5fef887ac4ef56
> Author: Paul E. McKenney <paulmck@kernel.org>
> Date:   Thu May 30 10:11:31 2024 -0700
> 
>     ARM: Emulate one-byte cmpxchg
>     
>     Use the new cmpxchg_emu_u8() to emulate one-byte cmpxchg() on ARM systems
>     with ARCH < ARMv6K.
>     
>     [ paulmck: Apply Arnd Bergmann and Nathan Chancellor feedback. ]
>     
>     Reported-by: Mark Brown <broonie@kernel.org>
>     Closes: https://lore.kernel.org/all/54798f68-48f7-4c65-9cba-47c0bf175143@sirena.org.uk/
>     Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
>     Closes: https://lore.kernel.org/all/CA+G9fYuZ+pf6p8AXMZWtdFtX-gbG8HMaBKp=XbxcdzA_QeLkxQ@mail.gmail.com/
>     Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
>     Cc: "Russell King (Oracle)" <rmk+kernel@armlinux.org.uk>
>     Cc: Arnd Bergmann <arnd@arndb.de>
>     Cc: Andrew Davis <afd@ti.com>
>     Cc: Andrew Morton <akpm@linux-foundation.org>
>     Cc: Linus Walleij <linus.walleij@linaro.org>
>     Cc: Eric DeVolder <eric.devolder@oracle.com>
>     Cc: Rob Herring <robh@kernel.org>
>     Cc: <linux-arm-kernel@lists.infradead.org>
> 
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index ee5115252aac4..a867a7d967aa5 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -34,6 +34,7 @@ config ARM
>  	select ARCH_MIGHT_HAVE_PC_PARPORT
>  	select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX
>  	select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT if CPU_V7
> +	select ARCH_NEED_CMPXCHG_1_EMU if CPU_V6
>  	select ARCH_SUPPORTS_ATOMIC_RMW
>  	select ARCH_SUPPORTS_CFI_CLANG
>  	select ARCH_SUPPORTS_HUGETLBFS if ARM_LPAE
> diff --git a/arch/arm/include/asm/cmpxchg.h b/arch/arm/include/asm/cmpxchg.h
> index 44667bdb4707a..a428e06fe94ee 100644
> --- a/arch/arm/include/asm/cmpxchg.h
> +++ b/arch/arm/include/asm/cmpxchg.h
> @@ -5,6 +5,7 @@
>  #include <linux/irqflags.h>
>  #include <linux/prefetch.h>
>  #include <asm/barrier.h>
> +#include <linux/cmpxchg-emu.h>
>  
>  #if defined(CONFIG_CPU_SA1100) || defined(CONFIG_CPU_SA110)
>  /*
> @@ -162,7 +163,11 @@ static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
>  	prefetchw((const void *)ptr);
>  
>  	switch (size) {
> -#ifndef CONFIG_CPU_V6	/* min ARCH >= ARMv6K */
> +#ifdef CONFIG_CPU_V6	/* min ARCH < ARMv6K */
> +	case 1:
> +		oldval = cmpxchg_emu_u8((volatile u8 *)ptr, old, new);
> +		break;
> +#else /* min ARCH >= ARMv6K */
>  	case 1:
>  		do {
>  			asm volatile("@ __cmpxchg1\n"

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Re: arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4): more undefined references to `__bad_cmpxchg' follow

[Paul E. McKenney]

On Thu, May 30, 2024 at 04:30:53PM -0700, Nathan Chancellor wrote:
> On Thu, May 30, 2024 at 03:05:21PM -0700, Paul E. McKenney wrote:
> > On Thu, May 30, 2024 at 02:52:48PM -0700, Nathan Chancellor wrote:
> > > On Thu, May 30, 2024 at 10:24:05AM -0700, Paul E. McKenney wrote:
> > > > And for an untested first attempt at a fix.
> > > > 
> > > > What did I mess up this time?  ;-)
> > > 
> > > An include for cmpxchg-emu.h ;)
> > > 
> > >   In file included from arch/arm/include/asm/atomic.h:16,
> > >                    from include/linux/atomic.h:7,
> > >                    from include/asm-generic/bitops/lock.h:5,
> > >                    from arch/arm/include/asm/bitops.h:245,
> > >                    from include/linux/bitops.h:63,
> > >                    from include/linux/log2.h:12,
> > >                    from kernel/bounds.c:13:
> > >   arch/arm/include/asm/cmpxchg.h: In function '__cmpxchg':
> > >   arch/arm/include/asm/cmpxchg.h:167:26: error: implicit declaration of function 'cmpxchg_emu_u8' [-Werror=implicit-function-declaration]
> > >     167 |                 oldval = cmpxchg_emu_u8((volatile u8 *)ptr, old, new);
> > >         |                          ^~~~~~~~~~~~~~
> > >   cc1: some warnings being treated as errors
> > 
> > Good catch, and thank you for testing this!  Does the updated version
> > shown below do better?
> 
> Yes, that matches what I tested locally before I replied initially.

Very good!  May I please add your Tested-by?

							Thanx, Paul

> Thanks for the quick fix!
> 
> Cheers,
> Nathan
> 
> > 							Thanx, Paul
> > 
> > ------------------------------------------------------------------------
> > 
> > commit 74e3470afacaa9d2f37db4773a5fef887ac4ef56
> > Author: Paul E. McKenney <paulmck@kernel.org>
> > Date:   Thu May 30 10:11:31 2024 -0700
> > 
> >     ARM: Emulate one-byte cmpxchg
> >     
> >     Use the new cmpxchg_emu_u8() to emulate one-byte cmpxchg() on ARM systems
> >     with ARCH < ARMv6K.
> >     
> >     [ paulmck: Apply Arnd Bergmann and Nathan Chancellor feedback. ]
> >     
> >     Reported-by: Mark Brown <broonie@kernel.org>
> >     Closes: https://lore.kernel.org/all/54798f68-48f7-4c65-9cba-47c0bf175143@sirena.org.uk/
> >     Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
> >     Closes: https://lore.kernel.org/all/CA+G9fYuZ+pf6p8AXMZWtdFtX-gbG8HMaBKp=XbxcdzA_QeLkxQ@mail.gmail.com/
> >     Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> >     Cc: "Russell King (Oracle)" <rmk+kernel@armlinux.org.uk>
> >     Cc: Arnd Bergmann <arnd@arndb.de>
> >     Cc: Andrew Davis <afd@ti.com>
> >     Cc: Andrew Morton <akpm@linux-foundation.org>
> >     Cc: Linus Walleij <linus.walleij@linaro.org>
> >     Cc: Eric DeVolder <eric.devolder@oracle.com>
> >     Cc: Rob Herring <robh@kernel.org>
> >     Cc: <linux-arm-kernel@lists.infradead.org>
> > 
> > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> > index ee5115252aac4..a867a7d967aa5 100644
> > --- a/arch/arm/Kconfig
> > +++ b/arch/arm/Kconfig
> > @@ -34,6 +34,7 @@ config ARM
> >  	select ARCH_MIGHT_HAVE_PC_PARPORT
> >  	select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX
> >  	select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT if CPU_V7
> > +	select ARCH_NEED_CMPXCHG_1_EMU if CPU_V6
> >  	select ARCH_SUPPORTS_ATOMIC_RMW
> >  	select ARCH_SUPPORTS_CFI_CLANG
> >  	select ARCH_SUPPORTS_HUGETLBFS if ARM_LPAE
> > diff --git a/arch/arm/include/asm/cmpxchg.h b/arch/arm/include/asm/cmpxchg.h
> > index 44667bdb4707a..a428e06fe94ee 100644
> > --- a/arch/arm/include/asm/cmpxchg.h
> > +++ b/arch/arm/include/asm/cmpxchg.h
> > @@ -5,6 +5,7 @@
> >  #include <linux/irqflags.h>
> >  #include <linux/prefetch.h>
> >  #include <asm/barrier.h>
> > +#include <linux/cmpxchg-emu.h>
> >  
> >  #if defined(CONFIG_CPU_SA1100) || defined(CONFIG_CPU_SA110)
> >  /*
> > @@ -162,7 +163,11 @@ static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
> >  	prefetchw((const void *)ptr);
> >  
> >  	switch (size) {
> > -#ifndef CONFIG_CPU_V6	/* min ARCH >= ARMv6K */
> > +#ifdef CONFIG_CPU_V6	/* min ARCH < ARMv6K */
> > +	case 1:
> > +		oldval = cmpxchg_emu_u8((volatile u8 *)ptr, old, new);
> > +		break;
> > +#else /* min ARCH >= ARMv6K */
> >  	case 1:
> >  		do {
> >  			asm volatile("@ __cmpxchg1\n"

Re: arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4): more undefined references to `__bad_cmpxchg' follow

[Paul E. McKenney]

On Thu, May 30, 2024 at 04:30:53PM -0700, Nathan Chancellor wrote:
> On Thu, May 30, 2024 at 03:05:21PM -0700, Paul E. McKenney wrote:
> > On Thu, May 30, 2024 at 02:52:48PM -0700, Nathan Chancellor wrote:
> > > On Thu, May 30, 2024 at 10:24:05AM -0700, Paul E. McKenney wrote:
> > > > And for an untested first attempt at a fix.
> > > > 
> > > > What did I mess up this time?  ;-)
> > > 
> > > An include for cmpxchg-emu.h ;)
> > > 
> > >   In file included from arch/arm/include/asm/atomic.h:16,
> > >                    from include/linux/atomic.h:7,
> > >                    from include/asm-generic/bitops/lock.h:5,
> > >                    from arch/arm/include/asm/bitops.h:245,
> > >                    from include/linux/bitops.h:63,
> > >                    from include/linux/log2.h:12,
> > >                    from kernel/bounds.c:13:
> > >   arch/arm/include/asm/cmpxchg.h: In function '__cmpxchg':
> > >   arch/arm/include/asm/cmpxchg.h:167:26: error: implicit declaration of function 'cmpxchg_emu_u8' [-Werror=implicit-function-declaration]
> > >     167 |                 oldval = cmpxchg_emu_u8((volatile u8 *)ptr, old, new);
> > >         |                          ^~~~~~~~~~~~~~
> > >   cc1: some warnings being treated as errors
> > 
> > Good catch, and thank you for testing this!  Does the updated version
> > shown below do better?
> 
> Yes, that matches what I tested locally before I replied initially.

Very good!  May I please add your Tested-by?

							Thanx, Paul

> Thanks for the quick fix!
> 
> Cheers,
> Nathan
> 
> > 							Thanx, Paul
> > 
> > ------------------------------------------------------------------------
> > 
> > commit 74e3470afacaa9d2f37db4773a5fef887ac4ef56
> > Author: Paul E. McKenney <paulmck@kernel.org>
> > Date:   Thu May 30 10:11:31 2024 -0700
> > 
> >     ARM: Emulate one-byte cmpxchg
> >     
> >     Use the new cmpxchg_emu_u8() to emulate one-byte cmpxchg() on ARM systems
> >     with ARCH < ARMv6K.
> >     
> >     [ paulmck: Apply Arnd Bergmann and Nathan Chancellor feedback. ]
> >     
> >     Reported-by: Mark Brown <broonie@kernel.org>
> >     Closes: https://lore.kernel.org/all/54798f68-48f7-4c65-9cba-47c0bf175143@sirena.org.uk/
> >     Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
> >     Closes: https://lore.kernel.org/all/CA+G9fYuZ+pf6p8AXMZWtdFtX-gbG8HMaBKp=XbxcdzA_QeLkxQ@mail.gmail.com/
> >     Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> >     Cc: "Russell King (Oracle)" <rmk+kernel@armlinux.org.uk>
> >     Cc: Arnd Bergmann <arnd@arndb.de>
> >     Cc: Andrew Davis <afd@ti.com>
> >     Cc: Andrew Morton <akpm@linux-foundation.org>
> >     Cc: Linus Walleij <linus.walleij@linaro.org>
> >     Cc: Eric DeVolder <eric.devolder@oracle.com>
> >     Cc: Rob Herring <robh@kernel.org>
> >     Cc: <linux-arm-kernel@lists.infradead.org>
> > 
> > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> > index ee5115252aac4..a867a7d967aa5 100644
> > --- a/arch/arm/Kconfig
> > +++ b/arch/arm/Kconfig
> > @@ -34,6 +34,7 @@ config ARM
> >  	select ARCH_MIGHT_HAVE_PC_PARPORT
> >  	select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX
> >  	select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT if CPU_V7
> > +	select ARCH_NEED_CMPXCHG_1_EMU if CPU_V6
> >  	select ARCH_SUPPORTS_ATOMIC_RMW
> >  	select ARCH_SUPPORTS_CFI_CLANG
> >  	select ARCH_SUPPORTS_HUGETLBFS if ARM_LPAE
> > diff --git a/arch/arm/include/asm/cmpxchg.h b/arch/arm/include/asm/cmpxchg.h
> > index 44667bdb4707a..a428e06fe94ee 100644
> > --- a/arch/arm/include/asm/cmpxchg.h
> > +++ b/arch/arm/include/asm/cmpxchg.h
> > @@ -5,6 +5,7 @@
> >  #include <linux/irqflags.h>
> >  #include <linux/prefetch.h>
> >  #include <asm/barrier.h>
> > +#include <linux/cmpxchg-emu.h>
> >  
> >  #if defined(CONFIG_CPU_SA1100) || defined(CONFIG_CPU_SA110)
> >  /*
> > @@ -162,7 +163,11 @@ static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
> >  	prefetchw((const void *)ptr);
> >  
> >  	switch (size) {
> > -#ifndef CONFIG_CPU_V6	/* min ARCH >= ARMv6K */
> > +#ifdef CONFIG_CPU_V6	/* min ARCH < ARMv6K */
> > +	case 1:
> > +		oldval = cmpxchg_emu_u8((volatile u8 *)ptr, old, new);
> > +		break;
> > +#else /* min ARCH >= ARMv6K */
> >  	case 1:
> >  		do {
> >  			asm volatile("@ __cmpxchg1\n"

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Re: arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4): more undefined references to `__bad_cmpxchg' follow

[Nathan Chancellor]

On Thu, May 30, 2024 at 05:35:44PM -0700, Paul E. McKenney wrote:
> On Thu, May 30, 2024 at 04:30:53PM -0700, Nathan Chancellor wrote:
> > On Thu, May 30, 2024 at 03:05:21PM -0700, Paul E. McKenney wrote:
> > > On Thu, May 30, 2024 at 02:52:48PM -0700, Nathan Chancellor wrote:
> > > > On Thu, May 30, 2024 at 10:24:05AM -0700, Paul E. McKenney wrote:
> > > > > And for an untested first attempt at a fix.
> > > > > 
> > > > > What did I mess up this time?  ;-)
> > > > 
> > > > An include for cmpxchg-emu.h ;)
> > > > 
> > > >   In file included from arch/arm/include/asm/atomic.h:16,
> > > >                    from include/linux/atomic.h:7,
> > > >                    from include/asm-generic/bitops/lock.h:5,
> > > >                    from arch/arm/include/asm/bitops.h:245,
> > > >                    from include/linux/bitops.h:63,
> > > >                    from include/linux/log2.h:12,
> > > >                    from kernel/bounds.c:13:
> > > >   arch/arm/include/asm/cmpxchg.h: In function '__cmpxchg':
> > > >   arch/arm/include/asm/cmpxchg.h:167:26: error: implicit declaration of function 'cmpxchg_emu_u8' [-Werror=implicit-function-declaration]
> > > >     167 |                 oldval = cmpxchg_emu_u8((volatile u8 *)ptr, old, new);
> > > >         |                          ^~~~~~~~~~~~~~
> > > >   cc1: some warnings being treated as errors
> > > 
> > > Good catch, and thank you for testing this!  Does the updated version
> > > shown below do better?
> > 
> > Yes, that matches what I tested locally before I replied initially.
> 
> Very good!  May I please add your Tested-by?

Sure thing.

Tested-by: Nathan Chancellor <nathan@kernel.org>

> > > ------------------------------------------------------------------------
> > > 
> > > commit 74e3470afacaa9d2f37db4773a5fef887ac4ef56
> > > Author: Paul E. McKenney <paulmck@kernel.org>
> > > Date:   Thu May 30 10:11:31 2024 -0700
> > > 
> > >     ARM: Emulate one-byte cmpxchg
> > >     
> > >     Use the new cmpxchg_emu_u8() to emulate one-byte cmpxchg() on ARM systems
> > >     with ARCH < ARMv6K.
> > >     
> > >     [ paulmck: Apply Arnd Bergmann and Nathan Chancellor feedback. ]
> > >     
> > >     Reported-by: Mark Brown <broonie@kernel.org>
> > >     Closes: https://lore.kernel.org/all/54798f68-48f7-4c65-9cba-47c0bf175143@sirena.org.uk/
> > >     Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
> > >     Closes: https://lore.kernel.org/all/CA+G9fYuZ+pf6p8AXMZWtdFtX-gbG8HMaBKp=XbxcdzA_QeLkxQ@mail.gmail.com/
> > >     Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> > >     Cc: "Russell King (Oracle)" <rmk+kernel@armlinux.org.uk>
> > >     Cc: Arnd Bergmann <arnd@arndb.de>
> > >     Cc: Andrew Davis <afd@ti.com>
> > >     Cc: Andrew Morton <akpm@linux-foundation.org>
> > >     Cc: Linus Walleij <linus.walleij@linaro.org>
> > >     Cc: Eric DeVolder <eric.devolder@oracle.com>
> > >     Cc: Rob Herring <robh@kernel.org>
> > >     Cc: <linux-arm-kernel@lists.infradead.org>
> > > 
> > > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> > > index ee5115252aac4..a867a7d967aa5 100644
> > > --- a/arch/arm/Kconfig
> > > +++ b/arch/arm/Kconfig
> > > @@ -34,6 +34,7 @@ config ARM
> > >  	select ARCH_MIGHT_HAVE_PC_PARPORT
> > >  	select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX
> > >  	select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT if CPU_V7
> > > +	select ARCH_NEED_CMPXCHG_1_EMU if CPU_V6
> > >  	select ARCH_SUPPORTS_ATOMIC_RMW
> > >  	select ARCH_SUPPORTS_CFI_CLANG
> > >  	select ARCH_SUPPORTS_HUGETLBFS if ARM_LPAE
> > > diff --git a/arch/arm/include/asm/cmpxchg.h b/arch/arm/include/asm/cmpxchg.h
> > > index 44667bdb4707a..a428e06fe94ee 100644
> > > --- a/arch/arm/include/asm/cmpxchg.h
> > > +++ b/arch/arm/include/asm/cmpxchg.h
> > > @@ -5,6 +5,7 @@
> > >  #include <linux/irqflags.h>
> > >  #include <linux/prefetch.h>
> > >  #include <asm/barrier.h>
> > > +#include <linux/cmpxchg-emu.h>
> > >  
> > >  #if defined(CONFIG_CPU_SA1100) || defined(CONFIG_CPU_SA110)
> > >  /*
> > > @@ -162,7 +163,11 @@ static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
> > >  	prefetchw((const void *)ptr);
> > >  
> > >  	switch (size) {
> > > -#ifndef CONFIG_CPU_V6	/* min ARCH >= ARMv6K */
> > > +#ifdef CONFIG_CPU_V6	/* min ARCH < ARMv6K */
> > > +	case 1:
> > > +		oldval = cmpxchg_emu_u8((volatile u8 *)ptr, old, new);
> > > +		break;
> > > +#else /* min ARCH >= ARMv6K */
> > >  	case 1:
> > >  		do {
> > >  			asm volatile("@ __cmpxchg1\n"

Re: arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4): more undefined references to `__bad_cmpxchg' follow

[Nathan Chancellor]

On Thu, May 30, 2024 at 05:35:44PM -0700, Paul E. McKenney wrote:
> On Thu, May 30, 2024 at 04:30:53PM -0700, Nathan Chancellor wrote:
> > On Thu, May 30, 2024 at 03:05:21PM -0700, Paul E. McKenney wrote:
> > > On Thu, May 30, 2024 at 02:52:48PM -0700, Nathan Chancellor wrote:
> > > > On Thu, May 30, 2024 at 10:24:05AM -0700, Paul E. McKenney wrote:
> > > > > And for an untested first attempt at a fix.
> > > > > 
> > > > > What did I mess up this time?  ;-)
> > > > 
> > > > An include for cmpxchg-emu.h ;)
> > > > 
> > > >   In file included from arch/arm/include/asm/atomic.h:16,
> > > >                    from include/linux/atomic.h:7,
> > > >                    from include/asm-generic/bitops/lock.h:5,
> > > >                    from arch/arm/include/asm/bitops.h:245,
> > > >                    from include/linux/bitops.h:63,
> > > >                    from include/linux/log2.h:12,
> > > >                    from kernel/bounds.c:13:
> > > >   arch/arm/include/asm/cmpxchg.h: In function '__cmpxchg':
> > > >   arch/arm/include/asm/cmpxchg.h:167:26: error: implicit declaration of function 'cmpxchg_emu_u8' [-Werror=implicit-function-declaration]
> > > >     167 |                 oldval = cmpxchg_emu_u8((volatile u8 *)ptr, old, new);
> > > >         |                          ^~~~~~~~~~~~~~
> > > >   cc1: some warnings being treated as errors
> > > 
> > > Good catch, and thank you for testing this!  Does the updated version
> > > shown below do better?
> > 
> > Yes, that matches what I tested locally before I replied initially.
> 
> Very good!  May I please add your Tested-by?

Sure thing.

Tested-by: Nathan Chancellor <nathan@kernel.org>

> > > ------------------------------------------------------------------------
> > > 
> > > commit 74e3470afacaa9d2f37db4773a5fef887ac4ef56
> > > Author: Paul E. McKenney <paulmck@kernel.org>
> > > Date:   Thu May 30 10:11:31 2024 -0700
> > > 
> > >     ARM: Emulate one-byte cmpxchg
> > >     
> > >     Use the new cmpxchg_emu_u8() to emulate one-byte cmpxchg() on ARM systems
> > >     with ARCH < ARMv6K.
> > >     
> > >     [ paulmck: Apply Arnd Bergmann and Nathan Chancellor feedback. ]
> > >     
> > >     Reported-by: Mark Brown <broonie@kernel.org>
> > >     Closes: https://lore.kernel.org/all/54798f68-48f7-4c65-9cba-47c0bf175143@sirena.org.uk/
> > >     Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
> > >     Closes: https://lore.kernel.org/all/CA+G9fYuZ+pf6p8AXMZWtdFtX-gbG8HMaBKp=XbxcdzA_QeLkxQ@mail.gmail.com/
> > >     Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> > >     Cc: "Russell King (Oracle)" <rmk+kernel@armlinux.org.uk>
> > >     Cc: Arnd Bergmann <arnd@arndb.de>
> > >     Cc: Andrew Davis <afd@ti.com>
> > >     Cc: Andrew Morton <akpm@linux-foundation.org>
> > >     Cc: Linus Walleij <linus.walleij@linaro.org>
> > >     Cc: Eric DeVolder <eric.devolder@oracle.com>
> > >     Cc: Rob Herring <robh@kernel.org>
> > >     Cc: <linux-arm-kernel@lists.infradead.org>
> > > 
> > > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> > > index ee5115252aac4..a867a7d967aa5 100644
> > > --- a/arch/arm/Kconfig
> > > +++ b/arch/arm/Kconfig
> > > @@ -34,6 +34,7 @@ config ARM
> > >  	select ARCH_MIGHT_HAVE_PC_PARPORT
> > >  	select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX
> > >  	select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT if CPU_V7
> > > +	select ARCH_NEED_CMPXCHG_1_EMU if CPU_V6
> > >  	select ARCH_SUPPORTS_ATOMIC_RMW
> > >  	select ARCH_SUPPORTS_CFI_CLANG
> > >  	select ARCH_SUPPORTS_HUGETLBFS if ARM_LPAE
> > > diff --git a/arch/arm/include/asm/cmpxchg.h b/arch/arm/include/asm/cmpxchg.h
> > > index 44667bdb4707a..a428e06fe94ee 100644
> > > --- a/arch/arm/include/asm/cmpxchg.h
> > > +++ b/arch/arm/include/asm/cmpxchg.h
> > > @@ -5,6 +5,7 @@
> > >  #include <linux/irqflags.h>
> > >  #include <linux/prefetch.h>
> > >  #include <asm/barrier.h>
> > > +#include <linux/cmpxchg-emu.h>
> > >  
> > >  #if defined(CONFIG_CPU_SA1100) || defined(CONFIG_CPU_SA110)
> > >  /*
> > > @@ -162,7 +163,11 @@ static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
> > >  	prefetchw((const void *)ptr);
> > >  
> > >  	switch (size) {
> > > -#ifndef CONFIG_CPU_V6	/* min ARCH >= ARMv6K */
> > > +#ifdef CONFIG_CPU_V6	/* min ARCH < ARMv6K */
> > > +	case 1:
> > > +		oldval = cmpxchg_emu_u8((volatile u8 *)ptr, old, new);
> > > +		break;
> > > +#else /* min ARCH >= ARMv6K */
> > >  	case 1:
> > >  		do {
> > >  			asm volatile("@ __cmpxchg1\n"

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Re: arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4): more undefined references to `__bad_cmpxchg' follow

[Paul E. McKenney]

On Fri, May 31, 2024 at 09:27:22AM -0700, Nathan Chancellor wrote:
> On Thu, May 30, 2024 at 05:35:44PM -0700, Paul E. McKenney wrote:
> > On Thu, May 30, 2024 at 04:30:53PM -0700, Nathan Chancellor wrote:
> > > On Thu, May 30, 2024 at 03:05:21PM -0700, Paul E. McKenney wrote:
> > > > On Thu, May 30, 2024 at 02:52:48PM -0700, Nathan Chancellor wrote:
> > > > > On Thu, May 30, 2024 at 10:24:05AM -0700, Paul E. McKenney wrote:
> > > > > > And for an untested first attempt at a fix.
> > > > > > 
> > > > > > What did I mess up this time?  ;-)
> > > > > 
> > > > > An include for cmpxchg-emu.h ;)
> > > > > 
> > > > >   In file included from arch/arm/include/asm/atomic.h:16,
> > > > >                    from include/linux/atomic.h:7,
> > > > >                    from include/asm-generic/bitops/lock.h:5,
> > > > >                    from arch/arm/include/asm/bitops.h:245,
> > > > >                    from include/linux/bitops.h:63,
> > > > >                    from include/linux/log2.h:12,
> > > > >                    from kernel/bounds.c:13:
> > > > >   arch/arm/include/asm/cmpxchg.h: In function '__cmpxchg':
> > > > >   arch/arm/include/asm/cmpxchg.h:167:26: error: implicit declaration of function 'cmpxchg_emu_u8' [-Werror=implicit-function-declaration]
> > > > >     167 |                 oldval = cmpxchg_emu_u8((volatile u8 *)ptr, old, new);
> > > > >         |                          ^~~~~~~~~~~~~~
> > > > >   cc1: some warnings being treated as errors
> > > > 
> > > > Good catch, and thank you for testing this!  Does the updated version
> > > > shown below do better?
> > > 
> > > Yes, that matches what I tested locally before I replied initially.
> > 
> > Very good!  May I please add your Tested-by?
> 
> Sure thing.
> 
> Tested-by: Nathan Chancellor <nathan@kernel.org>

Thank you!  I will apply this on my next rebase.

							Thanx, Paul

> > > > ------------------------------------------------------------------------
> > > > 
> > > > commit 74e3470afacaa9d2f37db4773a5fef887ac4ef56
> > > > Author: Paul E. McKenney <paulmck@kernel.org>
> > > > Date:   Thu May 30 10:11:31 2024 -0700
> > > > 
> > > >     ARM: Emulate one-byte cmpxchg
> > > >     
> > > >     Use the new cmpxchg_emu_u8() to emulate one-byte cmpxchg() on ARM systems
> > > >     with ARCH < ARMv6K.
> > > >     
> > > >     [ paulmck: Apply Arnd Bergmann and Nathan Chancellor feedback. ]
> > > >     
> > > >     Reported-by: Mark Brown <broonie@kernel.org>
> > > >     Closes: https://lore.kernel.org/all/54798f68-48f7-4c65-9cba-47c0bf175143@sirena.org.uk/
> > > >     Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
> > > >     Closes: https://lore.kernel.org/all/CA+G9fYuZ+pf6p8AXMZWtdFtX-gbG8HMaBKp=XbxcdzA_QeLkxQ@mail.gmail.com/
> > > >     Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> > > >     Cc: "Russell King (Oracle)" <rmk+kernel@armlinux.org.uk>
> > > >     Cc: Arnd Bergmann <arnd@arndb.de>
> > > >     Cc: Andrew Davis <afd@ti.com>
> > > >     Cc: Andrew Morton <akpm@linux-foundation.org>
> > > >     Cc: Linus Walleij <linus.walleij@linaro.org>
> > > >     Cc: Eric DeVolder <eric.devolder@oracle.com>
> > > >     Cc: Rob Herring <robh@kernel.org>
> > > >     Cc: <linux-arm-kernel@lists.infradead.org>
> > > > 
> > > > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> > > > index ee5115252aac4..a867a7d967aa5 100644
> > > > --- a/arch/arm/Kconfig
> > > > +++ b/arch/arm/Kconfig
> > > > @@ -34,6 +34,7 @@ config ARM
> > > >  	select ARCH_MIGHT_HAVE_PC_PARPORT
> > > >  	select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX
> > > >  	select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT if CPU_V7
> > > > +	select ARCH_NEED_CMPXCHG_1_EMU if CPU_V6
> > > >  	select ARCH_SUPPORTS_ATOMIC_RMW
> > > >  	select ARCH_SUPPORTS_CFI_CLANG
> > > >  	select ARCH_SUPPORTS_HUGETLBFS if ARM_LPAE
> > > > diff --git a/arch/arm/include/asm/cmpxchg.h b/arch/arm/include/asm/cmpxchg.h
> > > > index 44667bdb4707a..a428e06fe94ee 100644
> > > > --- a/arch/arm/include/asm/cmpxchg.h
> > > > +++ b/arch/arm/include/asm/cmpxchg.h
> > > > @@ -5,6 +5,7 @@
> > > >  #include <linux/irqflags.h>
> > > >  #include <linux/prefetch.h>
> > > >  #include <asm/barrier.h>
> > > > +#include <linux/cmpxchg-emu.h>
> > > >  
> > > >  #if defined(CONFIG_CPU_SA1100) || defined(CONFIG_CPU_SA110)
> > > >  /*
> > > > @@ -162,7 +163,11 @@ static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
> > > >  	prefetchw((const void *)ptr);
> > > >  
> > > >  	switch (size) {
> > > > -#ifndef CONFIG_CPU_V6	/* min ARCH >= ARMv6K */
> > > > +#ifdef CONFIG_CPU_V6	/* min ARCH < ARMv6K */
> > > > +	case 1:
> > > > +		oldval = cmpxchg_emu_u8((volatile u8 *)ptr, old, new);
> > > > +		break;
> > > > +#else /* min ARCH >= ARMv6K */
> > > >  	case 1:
> > > >  		do {
> > > >  			asm volatile("@ __cmpxchg1\n"

Re: arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4): more undefined references to `__bad_cmpxchg' follow

[Paul E. McKenney]

On Fri, May 31, 2024 at 09:27:22AM -0700, Nathan Chancellor wrote:
> On Thu, May 30, 2024 at 05:35:44PM -0700, Paul E. McKenney wrote:
> > On Thu, May 30, 2024 at 04:30:53PM -0700, Nathan Chancellor wrote:
> > > On Thu, May 30, 2024 at 03:05:21PM -0700, Paul E. McKenney wrote:
> > > > On Thu, May 30, 2024 at 02:52:48PM -0700, Nathan Chancellor wrote:
> > > > > On Thu, May 30, 2024 at 10:24:05AM -0700, Paul E. McKenney wrote:
> > > > > > And for an untested first attempt at a fix.
> > > > > > 
> > > > > > What did I mess up this time?  ;-)
> > > > > 
> > > > > An include for cmpxchg-emu.h ;)
> > > > > 
> > > > >   In file included from arch/arm/include/asm/atomic.h:16,
> > > > >                    from include/linux/atomic.h:7,
> > > > >                    from include/asm-generic/bitops/lock.h:5,
> > > > >                    from arch/arm/include/asm/bitops.h:245,
> > > > >                    from include/linux/bitops.h:63,
> > > > >                    from include/linux/log2.h:12,
> > > > >                    from kernel/bounds.c:13:
> > > > >   arch/arm/include/asm/cmpxchg.h: In function '__cmpxchg':
> > > > >   arch/arm/include/asm/cmpxchg.h:167:26: error: implicit declaration of function 'cmpxchg_emu_u8' [-Werror=implicit-function-declaration]
> > > > >     167 |                 oldval = cmpxchg_emu_u8((volatile u8 *)ptr, old, new);
> > > > >         |                          ^~~~~~~~~~~~~~
> > > > >   cc1: some warnings being treated as errors
> > > > 
> > > > Good catch, and thank you for testing this!  Does the updated version
> > > > shown below do better?
> > > 
> > > Yes, that matches what I tested locally before I replied initially.
> > 
> > Very good!  May I please add your Tested-by?
> 
> Sure thing.
> 
> Tested-by: Nathan Chancellor <nathan@kernel.org>

Thank you!  I will apply this on my next rebase.

							Thanx, Paul

> > > > ------------------------------------------------------------------------
> > > > 
> > > > commit 74e3470afacaa9d2f37db4773a5fef887ac4ef56
> > > > Author: Paul E. McKenney <paulmck@kernel.org>
> > > > Date:   Thu May 30 10:11:31 2024 -0700
> > > > 
> > > >     ARM: Emulate one-byte cmpxchg
> > > >     
> > > >     Use the new cmpxchg_emu_u8() to emulate one-byte cmpxchg() on ARM systems
> > > >     with ARCH < ARMv6K.
> > > >     
> > > >     [ paulmck: Apply Arnd Bergmann and Nathan Chancellor feedback. ]
> > > >     
> > > >     Reported-by: Mark Brown <broonie@kernel.org>
> > > >     Closes: https://lore.kernel.org/all/54798f68-48f7-4c65-9cba-47c0bf175143@sirena.org.uk/
> > > >     Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
> > > >     Closes: https://lore.kernel.org/all/CA+G9fYuZ+pf6p8AXMZWtdFtX-gbG8HMaBKp=XbxcdzA_QeLkxQ@mail.gmail.com/
> > > >     Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> > > >     Cc: "Russell King (Oracle)" <rmk+kernel@armlinux.org.uk>
> > > >     Cc: Arnd Bergmann <arnd@arndb.de>
> > > >     Cc: Andrew Davis <afd@ti.com>
> > > >     Cc: Andrew Morton <akpm@linux-foundation.org>
> > > >     Cc: Linus Walleij <linus.walleij@linaro.org>
> > > >     Cc: Eric DeVolder <eric.devolder@oracle.com>
> > > >     Cc: Rob Herring <robh@kernel.org>
> > > >     Cc: <linux-arm-kernel@lists.infradead.org>
> > > > 
> > > > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> > > > index ee5115252aac4..a867a7d967aa5 100644
> > > > --- a/arch/arm/Kconfig
> > > > +++ b/arch/arm/Kconfig
> > > > @@ -34,6 +34,7 @@ config ARM
> > > >  	select ARCH_MIGHT_HAVE_PC_PARPORT
> > > >  	select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX
> > > >  	select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT if CPU_V7
> > > > +	select ARCH_NEED_CMPXCHG_1_EMU if CPU_V6
> > > >  	select ARCH_SUPPORTS_ATOMIC_RMW
> > > >  	select ARCH_SUPPORTS_CFI_CLANG
> > > >  	select ARCH_SUPPORTS_HUGETLBFS if ARM_LPAE
> > > > diff --git a/arch/arm/include/asm/cmpxchg.h b/arch/arm/include/asm/cmpxchg.h
> > > > index 44667bdb4707a..a428e06fe94ee 100644
> > > > --- a/arch/arm/include/asm/cmpxchg.h
> > > > +++ b/arch/arm/include/asm/cmpxchg.h
> > > > @@ -5,6 +5,7 @@
> > > >  #include <linux/irqflags.h>
> > > >  #include <linux/prefetch.h>
> > > >  #include <asm/barrier.h>
> > > > +#include <linux/cmpxchg-emu.h>
> > > >  
> > > >  #if defined(CONFIG_CPU_SA1100) || defined(CONFIG_CPU_SA110)
> > > >  /*
> > > > @@ -162,7 +163,11 @@ static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
> > > >  	prefetchw((const void *)ptr);
> > > >  
> > > >  	switch (size) {
> > > > -#ifndef CONFIG_CPU_V6	/* min ARCH >= ARMv6K */
> > > > +#ifdef CONFIG_CPU_V6	/* min ARCH < ARMv6K */
> > > > +	case 1:
> > > > +		oldval = cmpxchg_emu_u8((volatile u8 *)ptr, old, new);
> > > > +		break;
> > > > +#else /* min ARCH >= ARMv6K */
> > > >  	case 1:
> > > >  		do {
> > > >  			asm volatile("@ __cmpxchg1\n"

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