mainline build failure for loongarch allmodconfig with gcc-12

mainline build failure for loongarch allmodconfig with gcc-12

[Sudip Mukherjee (Codethink)]

Hi All,

I have been trying to build loongarch as part of my nightly builds, and
I can build loongson3_defconfig without any error. But allmodconfig fails
with the error:

In function '__cmpxchg',
    inlined from 'ssh_seq_next' at drivers/platform/surface/aggregator/controller.c:61:9,
    inlined from 'ssam_request_write_data' at drivers/platform/surface/aggregator/controller.c:1483:8,
    inlined from 'ssam_request_sync_with_buffer' at drivers/platform/surface/aggregator/controller.c:1761:8:
././include/linux/compiler_types.h:354:45: error: call to '__compiletime_assert_9' declared with attribute error: BUILD_BUG failed
  354 |         _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
      |                                             ^
././include/linux/compiler_types.h:335:25: note: in definition of macro '__compiletime_assert'
  335 |                         prefix ## suffix();                             \
      |                         ^~~~~~
././include/linux/compiler_types.h:354:9: note: in expansion of macro '_compiletime_assert'
  354 |         _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
      |         ^~~~~~~~~~~~~~~~~~~
./include/linux/build_bug.h:39:37: note: in expansion of macro 'compiletime_assert'
   39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
      |                                     ^~~~~~~~~~~~~~~~~~
./include/linux/build_bug.h:59:21: note: in expansion of macro 'BUILD_BUG_ON_MSG'
   59 | #define BUILD_BUG() BUILD_BUG_ON_MSG(1, "BUILD_BUG failed")
      |                     ^~~~~~~~~~~~~~~~
./arch/loongarch/include/asm/cmpxchg.h:83:17: note: in expansion of macro 'BUILD_BUG'
   83 |                 BUILD_BUG();
      |                 ^~~~~~~~~

I will be happy to test any patch or provide any extra log if needed.


-- 
Regards
Sudip

Re: mainline build failure for loongarch allmodconfig with gcc-12

[Linus Torvalds]

On Tue, Aug 23, 2022 at 1:34 AM Sudip Mukherjee (Codethink)
<sudipm.mukherjee@gmail.com> wrote:
>
> I have been trying to build loongarch as part of my nightly builds, and
> I can build loongson3_defconfig without any error. But allmodconfig fails
> with the error:
>
> In function '__cmpxchg',
>     inlined from 'ssh_seq_next' at drivers/platform/surface/aggregator/controller.c:61:9,

Looks like ssh_seq_next() wants to do an atomic cmpxchg() on a single
byte value, and the Loongarch implementation only does 4- and 8-byte
versions.

It looks like loongarch - from its MIPS heritage - inherited the "we
can't do atomics on byte variables", so that it needs the same strange
"do bytes as word accesses with mask-and-shifts".

For MIPS, the code is in __xchg_small() in arch/mips/kernel/cmpxchg.c.

Alpha has something similar, except it's all done in inline asm in
arch/alpha/include/asm/xchg.h (look for "____cmpxchg(_u8," in there.

Of course, we could just add a Kconfig variable like
"ARCH_LACKS_BYTE_ATOMICS" and make that driver depend on it not being
true, and just have Loongarch set it.

But I think loongarch should just implement the byte masking stuff.
Particularly since I suspect it can just copy the MIPS code as-is.

                  Linus

Re: mainline build failure for loongarch allmodconfig with gcc-12

[Huacai Chen]

Hi, Linus,

On Wed, Aug 24, 2022 at 2:09 AM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> On Tue, Aug 23, 2022 at 1:34 AM Sudip Mukherjee (Codethink)
> <sudipm.mukherjee@gmail.com> wrote:
> >
> > I have been trying to build loongarch as part of my nightly builds, and
> > I can build loongson3_defconfig without any error. But allmodconfig fails
> > with the error:
> >
> > In function '__cmpxchg',
> >     inlined from 'ssh_seq_next' at drivers/platform/surface/aggregator/controller.c:61:9,
>
> Looks like ssh_seq_next() wants to do an atomic cmpxchg() on a single
> byte value, and the Loongarch implementation only does 4- and 8-byte
> versions.
>
> It looks like loongarch - from its MIPS heritage - inherited the "we
> can't do atomics on byte variables", so that it needs the same strange
> "do bytes as word accesses with mask-and-shifts".
>
> For MIPS, the code is in __xchg_small() in arch/mips/kernel/cmpxchg.c.
>
> Alpha has something similar, except it's all done in inline asm in
> arch/alpha/include/asm/xchg.h (look for "____cmpxchg(_u8," in there.
>
> Of course, we could just add a Kconfig variable like
> "ARCH_LACKS_BYTE_ATOMICS" and make that driver depend on it not being
> true, and just have Loongarch set it.
>
> But I think loongarch should just implement the byte masking stuff.
> Particularly since I suspect it can just copy the MIPS code as-is.
Yes, I agree. There is already a proposed patch to do this [1]. It was
discussed for a long time about the "forward progress", but I think
that problem is solved because LoongArch has "exclusive access (with
timeout) of ll" and "random delay of sc" in hardware. So I hope this
patch can be accepted now.

https://lore.kernel.org/loongarch/CAJF2gTQBjetiA1eDaXhBsiEmRYCdOAAWWAGcwVjhZTBYH5BpGQ@mail.gmail.com/T/#m9df7f86d9509cec23a66a0304152377e1070b62e

Huacai
>
>                   Linus