clang/objtool failures on linux-next

clang/objtool failures on linux-next

[Arnd Bergmann]

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I came across two randconfig builds on linux-next that fail to build:

==> build/x86/0xCE0DD5F4_defconfig/log <==
drivers/input/misc/uinput.o: warning: objtool: uinput_str_to_user+0x165: undefined stack state
drivers/input/misc/uinput.o: warning: objtool: uinput_str_to_user+0x165: unknown CFA base reg -1

==> build/x86/0xAE77DEF6_defconfig/log <==
drivers/scsi/qla2xxx/qla_dbg.o: error: SIGSEGV: objtool stack overflow!
Segmentation fault

The first one happens with clang-18 through clang-22, the second one
with all versions of clang.

The crash seems worse at first, but I also noticed that
clang takes a long time to actually compile it, and the object
file is huge, so this is probably partially a compiler problem.

Please have a look at the attached object files along the configs
I used.

      Arnd

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Re: clang/objtool failures on linux-next

[Josh Poimboeuf]

On Fri, Mar 06, 2026 at 01:41:59PM +0100, Arnd Bergmann wrote:
> I came across two randconfig builds on linux-next that fail to build:
> 
> ==> build/x86/0xCE0DD5F4_defconfig/log <==
> drivers/input/misc/uinput.o: warning: objtool: uinput_str_to_user+0x165: undefined stack state
> drivers/input/misc/uinput.o: warning: objtool: uinput_str_to_user+0x165: unknown CFA base reg -1
> 
> ==> build/x86/0xAE77DEF6_defconfig/log <==
> drivers/scsi/qla2xxx/qla_dbg.o: error: SIGSEGV: objtool stack overflow!
> Segmentation fault
> 
> The first one happens with clang-18 through clang-22, the second one
> with all versions of clang.
> 
> The crash seems worse at first, but I also noticed that
> clang takes a long time to actually compile it, and the object
> file is huge, so this is probably partially a compiler problem.
> 
> Please have a look at the attached object files along the configs
> I used.

Thanks, I'll post a fix for the 1st one right now (haven't looked at the
stack overflow yet).


-- 
Josh

Re: clang/objtool failures on linux-next

[Josh Poimboeuf]

On Fri, Mar 06, 2026 at 09:31:02AM -0800, Josh Poimboeuf wrote:
> On Fri, Mar 06, 2026 at 01:41:59PM +0100, Arnd Bergmann wrote:
> > I came across two randconfig builds on linux-next that fail to build:
> > 
> > ==> build/x86/0xCE0DD5F4_defconfig/log <==
> > drivers/input/misc/uinput.o: warning: objtool: uinput_str_to_user+0x165: undefined stack state
> > drivers/input/misc/uinput.o: warning: objtool: uinput_str_to_user+0x165: unknown CFA base reg -1
> > 
> > ==> build/x86/0xAE77DEF6_defconfig/log <==
> > drivers/scsi/qla2xxx/qla_dbg.o: error: SIGSEGV: objtool stack overflow!
> > Segmentation fault
> > 
> > The first one happens with clang-18 through clang-22, the second one
> > with all versions of clang.
> > 
> > The crash seems worse at first, but I also noticed that
> > clang takes a long time to actually compile it, and the object
> > file is huge, so this is probably partially a compiler problem.
> > 
> > Please have a look at the attached object files along the configs
> > I used.
> 
> Thanks, I'll post a fix for the 1st one right now (haven't looked at the
> stack overflow yet).

Both fixes posted now:

https://lore.kernel.org/240e6a172cc73292499334a3724d02ccb3247fc7.1772818491.git.jpoimboe@kernel.org
https://lore.kernel.org/8b97f62d083457f3b0a29a424275f7957dd3372f.1772821683.git.jpoimboe@kernel.org

-- 
Josh

Re: clang/objtool failures on linux-next

[Arnd Bergmann]

On Fri, Mar 6, 2026, at 19:29, Josh Poimboeuf wrote:
> On Fri, Mar 06, 2026 at 09:31:02AM -0800, Josh Poimboeuf wrote:
>> On Fri, Mar 06, 2026 at 01:41:59PM +0100, Arnd Bergmann wrote:
>> 
>> Thanks, I'll post a fix for the 1st one right now (haven't looked at the
>> stack overflow yet).
>
> Both fixes posted now:
>
> https://lore.kernel.org/240e6a172cc73292499334a3724d02ccb3247fc7.1772818491.git.jpoimboe@kernel.org
> https://lore.kernel.org/8b97f62d083457f3b0a29a424275f7957dd3372f.1772821683.git.jpoimboe@kernel.org

Thanks a lot, that was quick!

I've applied both to my randconfig tree now and verified that
both issues are addressed in the full build. There is still
the question of the 0xAE77DEF6_defconfig causing an incredibly
long compile time (minutes!) for the one file when using clang.

I've added Nathan to Cc in case he is motivated to try to
reproduce this.

FWIW, this is the current set of objtool warnings that I get that
don't cause the build to fail:

drivers/gpu/drm/amd/amdgpu/amdgpu_cs.o: warning: objtool: amdgpu_cs_parser_bos+0x723: unreachable instruction
drivers/gpu/drm/msm/msm.o: warning: objtool: msm_gem_vm_close+0x1cf: unreachable instruction
drivers/gpu/drm/panthor/panthor.o: warning: objtool: panthor_ioctl_vm_bind+0x32b: __stack_chk_fail() missing __noreturn in .c/.h or NORETURN() in noreturns.h
drivers/gpu/drm/panthor/panthor.o: warning: objtool: panthor_ioctl_vm_bind_async+0x285: unreachable instruction
drivers/gpu/drm/panthor/panthor_drv.o: warning: objtool: panthor_ioctl_vm_bind+0x2df: unreachable instruction
drivers/gpu/drm/xe/xe_bo.o: warning: objtool: xe_bo_create_pin_map_at_novm+0x11d: unreachable instruction
drivers/iio/imu/bmi160/bmi160_core.o: warning: objtool: bmi160_setup_irq() falls through to next function __cfi_bmi160_core_runtime_resume()
kernel/bpf/core.o: warning: objtool: ___bpf_prog_run+0x217: sibling call from callable instruction with modified stack frame
sound/soc/codecs/wcd9335.o: warning: objtool: wcd9335_slimbus_irq() falls through to next function __cfi_wcd9335_set_channel_map()
vmlinux.o: warning: objtool: ___bpf_prog_run+0x1d4: sibling call from callable instruction with modified stack frame
vmlinux.o: warning: objtool: hdmi_power_on_full.isra.0+0xd6: hdmi_pll_compute() missing __noreturn in .c/.h or NORETURN() in noreturns.h

If you want to investigate those, I can send you the configs and/or
object files for these as well.

       Arnd

Re: clang/objtool failures on linux-next

[Josh Poimboeuf]

On Fri, Mar 06, 2026 at 10:02:54PM +0100, Arnd Bergmann wrote:
> On Fri, Mar 6, 2026, at 19:29, Josh Poimboeuf wrote:
> > On Fri, Mar 06, 2026 at 09:31:02AM -0800, Josh Poimboeuf wrote:
> >> On Fri, Mar 06, 2026 at 01:41:59PM +0100, Arnd Bergmann wrote:
> >> 
> >> Thanks, I'll post a fix for the 1st one right now (haven't looked at the
> >> stack overflow yet).
> >
> > Both fixes posted now:
> >
> > https://lore.kernel.org/240e6a172cc73292499334a3724d02ccb3247fc7.1772818491.git.jpoimboe@kernel.org
> > https://lore.kernel.org/8b97f62d083457f3b0a29a424275f7957dd3372f.1772821683.git.jpoimboe@kernel.org
> 
> Thanks a lot, that was quick!
> 
> I've applied both to my randconfig tree now and verified that
> both issues are addressed in the full build. There is still
> the question of the 0xAE77DEF6_defconfig causing an incredibly
> long compile time (minutes!) for the one file when using clang.
> 
> I've added Nathan to Cc in case he is motivated to try to
> reproduce this.
> 
> FWIW, this is the current set of objtool warnings that I get that
> don't cause the build to fail:
> 
> drivers/gpu/drm/amd/amdgpu/amdgpu_cs.o: warning: objtool: amdgpu_cs_parser_bos+0x723: unreachable instruction
> drivers/gpu/drm/msm/msm.o: warning: objtool: msm_gem_vm_close+0x1cf: unreachable instruction
> drivers/gpu/drm/panthor/panthor.o: warning: objtool: panthor_ioctl_vm_bind+0x32b: __stack_chk_fail() missing __noreturn in .c/.h or NORETURN() in noreturns.h
> drivers/gpu/drm/panthor/panthor.o: warning: objtool: panthor_ioctl_vm_bind_async+0x285: unreachable instruction
> drivers/gpu/drm/panthor/panthor_drv.o: warning: objtool: panthor_ioctl_vm_bind+0x2df: unreachable instruction
> drivers/gpu/drm/xe/xe_bo.o: warning: objtool: xe_bo_create_pin_map_at_novm+0x11d: unreachable instruction
> drivers/iio/imu/bmi160/bmi160_core.o: warning: objtool: bmi160_setup_irq() falls through to next function __cfi_bmi160_core_runtime_resume()
> kernel/bpf/core.o: warning: objtool: ___bpf_prog_run+0x217: sibling call from callable instruction with modified stack frame
> sound/soc/codecs/wcd9335.o: warning: objtool: wcd9335_slimbus_irq() falls through to next function __cfi_wcd9335_set_channel_map()
> vmlinux.o: warning: objtool: ___bpf_prog_run+0x1d4: sibling call from callable instruction with modified stack frame
> vmlinux.o: warning: objtool: hdmi_power_on_full.isra.0+0xd6: hdmi_pll_compute() missing __noreturn in .c/.h or NORETURN() in noreturns.h
> 
> If you want to investigate those, I can send you the configs and/or
> object files for these as well.

Yes, please send those and I'll take a look.  Thanks!

-- 
Josh

Re: clang/objtool failures on linux-next

[Arnd Bergmann]

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On Fri, Mar 6, 2026, at 22:17, Josh Poimboeuf wrote:
> On Fri, Mar 06, 2026 at 10:02:54PM +0100, Arnd Bergmann wrote:
>> 
>> drivers/gpu/drm/amd/amdgpu/amdgpu_cs.o: warning: objtool: amdgpu_cs_parser_bos+0x723: unreachable instruction
>> drivers/gpu/drm/msm/msm.o: warning: objtool: msm_gem_vm_close+0x1cf: unreachable instruction
>> drivers/gpu/drm/panthor/panthor.o: warning: objtool: panthor_ioctl_vm_bind+0x32b: __stack_chk_fail() missing __noreturn in .c/.h or NORETURN() in noreturns.h
>> drivers/gpu/drm/panthor/panthor.o: warning: objtool: panthor_ioctl_vm_bind_async+0x285: unreachable instruction
>> drivers/gpu/drm/panthor/panthor_drv.o: warning: objtool: panthor_ioctl_vm_bind+0x2df: unreachable instruction
>> drivers/gpu/drm/xe/xe_bo.o: warning: objtool: xe_bo_create_pin_map_at_novm+0x11d: unreachable instruction
>> drivers/iio/imu/bmi160/bmi160_core.o: warning: objtool: bmi160_setup_irq() falls through to next function __cfi_bmi160_core_runtime_resume()
>> kernel/bpf/core.o: warning: objtool: ___bpf_prog_run+0x217: sibling call from callable instruction with modified stack frame
>> sound/soc/codecs/wcd9335.o: warning: objtool: wcd9335_slimbus_irq() falls through to next function __cfi_wcd9335_set_channel_map()
>> vmlinux.o: warning: objtool: ___bpf_prog_run+0x1d4: sibling call from callable instruction with modified stack frame
>> vmlinux.o: warning: objtool: hdmi_power_on_full.isra.0+0xd6: hdmi_pll_compute() missing __noreturn in .c/.h or NORETURN() in noreturns.h
>> 
>> If you want to investigate those, I can send you the configs and/or
>> object files for these as well.
>
> Yes, please send those and I'll take a look.  Thanks!

These are the ones I could easily reproduce on today's linux-next:

==> build/x86/0xCE0DD5F4_defconfig/log <==
vmlinux.o: warning: objtool: ___bpf_prog_run+0x1c5: sibling call from callable instruction with modified stack frame

==> build/x86/0x8FD83285_defconfig/log <==
drivers/gpu/drm/amd/amdgpu/amdgpu_cs.o: warning: objtool: amdgpu_cs_parser_bos+0x723: unreachable instruction
drivers/gpu/drm/xe/xe_bo.o: warning: objtool: xe_bo_create_pin_map_at_novm+0x11d: unreachable instruction
drivers/gpu/drm/panthor/panthor_drv.o: warning: objtool: panthor_ioctl_vm_bind+0x2df: unreachable instruction
drivers/iio/imu/bmi160/bmi160_core.o: warning: objtool: bmi160_setup_irq() falls through to next function __cfi_bmi160_core_runtime_resume()

==> build/x86/0x4DF22811_defconfig/log <==
sound/soc/codecs/wcd9335.o: warning: objtool: wcd9335_slimbus_irq() falls through to next function __cfi_wcd9335_set_channel_map()

     Arnd


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Re: clang/objtool failures on linux-next

[Nathan Chancellor]

On Fri, Mar 06, 2026 at 10:02:54PM +0100, Arnd Bergmann wrote:
> I've added Nathan to Cc in case he is motivated to try to
> reproduce this.

Yeah, I will see if I can get something reproduced for the LLVM folks to
take a look at upstream. Most of the time it ends up being something
small and dumb :)

Cheers,
Nathan

Re: clang/objtool failures on linux-next

[Josh Poimboeuf]

On Fri, Mar 06, 2026 at 11:04:50PM +0100, Arnd Bergmann wrote:
> ==> build/x86/0x8FD83285_defconfig/log <==
> drivers/gpu/drm/amd/amdgpu/amdgpu_cs.o: warning: objtool: amdgpu_cs_parser_bos+0x723: unreachable instruction
> drivers/gpu/drm/xe/xe_bo.o: warning: objtool: xe_bo_create_pin_map_at_novm+0x11d: unreachable instruction
> drivers/gpu/drm/panthor/panthor_drv.o: warning: objtool: panthor_ioctl_vm_bind+0x2df: unreachable instruction

These three warnings are accurate, for each of these, Clang is leaving
an unreachable JMP at the end of the function:

    166e:	4c 89 ea             	mov    %r13,%rdx
    1671:	e8 00 00 00 00       	call   1676 <amdgpu_cs_parser_bos+0x716>	1672: R_X86_64_PLT32	__ubsan_handle_shift_out_of_bounds-0x4
    1676:	49 8b 94 24 08 1d 01 00 	mov    0x11d08(%r12),%rdx
    167e:	e9 c6 fd ff ff       	jmp    1449 <amdgpu_cs_parser_bos+0x4e9>
    1683:	e9 8c f9 ff ff       	jmp    1014 <amdgpu_cs_parser_bos+0xb4>
    1688:	0f 1f 84 00 00 00 00 00 	nopl   0x0(%rax,%rax,1)

Nathan, any idea?  I haven't seen this pattern before.

-- 
Josh

Re: clang/objtool failures on linux-next

[Josh Poimboeuf]

On Fri, Mar 06, 2026 at 11:04:50PM +0100, Arnd Bergmann wrote:
> On Fri, Mar 6, 2026, at 22:17, Josh Poimboeuf wrote:
> > On Fri, Mar 06, 2026 at 10:02:54PM +0100, Arnd Bergmann wrote:
> >> 
> >> drivers/gpu/drm/amd/amdgpu/amdgpu_cs.o: warning: objtool: amdgpu_cs_parser_bos+0x723: unreachable instruction
> >> drivers/gpu/drm/msm/msm.o: warning: objtool: msm_gem_vm_close+0x1cf: unreachable instruction
> >> drivers/gpu/drm/panthor/panthor.o: warning: objtool: panthor_ioctl_vm_bind+0x32b: __stack_chk_fail() missing __noreturn in .c/.h or NORETURN() in noreturns.h
> >> drivers/gpu/drm/panthor/panthor.o: warning: objtool: panthor_ioctl_vm_bind_async+0x285: unreachable instruction
> >> drivers/gpu/drm/panthor/panthor_drv.o: warning: objtool: panthor_ioctl_vm_bind+0x2df: unreachable instruction
> >> drivers/gpu/drm/xe/xe_bo.o: warning: objtool: xe_bo_create_pin_map_at_novm+0x11d: unreachable instruction
> >> drivers/iio/imu/bmi160/bmi160_core.o: warning: objtool: bmi160_setup_irq() falls through to next function __cfi_bmi160_core_runtime_resume()
> >> kernel/bpf/core.o: warning: objtool: ___bpf_prog_run+0x217: sibling call from callable instruction with modified stack frame
> >> sound/soc/codecs/wcd9335.o: warning: objtool: wcd9335_slimbus_irq() falls through to next function __cfi_wcd9335_set_channel_map()
> >> vmlinux.o: warning: objtool: ___bpf_prog_run+0x1d4: sibling call from callable instruction with modified stack frame
> >> vmlinux.o: warning: objtool: hdmi_power_on_full.isra.0+0xd6: hdmi_pll_compute() missing __noreturn in .c/.h or NORETURN() in noreturns.h
> >> 
> >> If you want to investigate those, I can send you the configs and/or
> >> object files for these as well.
> >
> > Yes, please send those and I'll take a look.  Thanks!
> 
> These are the ones I could easily reproduce on today's linux-next:
> 
> ==> build/x86/0xCE0DD5F4_defconfig/log <==
> vmlinux.o: warning: objtool: ___bpf_prog_run+0x1c5: sibling call from callable instruction with modified stack frame
> 
> ==> build/x86/0x8FD83285_defconfig/log <==
> ...
> drivers/iio/imu/bmi160/bmi160_core.o: warning: objtool: bmi160_setup_irq() falls through to next function __cfi_bmi160_core_runtime_resume()
> 
> ==> build/x86/0x4DF22811_defconfig/log <==
> sound/soc/codecs/wcd9335.o: warning: objtool: wcd9335_slimbus_irq() falls through to next function __cfi_wcd9335_set_channel_map()

I have fixes for these 3, will post the lot soonish.

-- 
Josh

Re: clang/objtool failures on linux-next

[Nathan Chancellor]

On Fri, Mar 06, 2026 at 05:35:20PM -0800, Josh Poimboeuf wrote:
> On Fri, Mar 06, 2026 at 11:04:50PM +0100, Arnd Bergmann wrote:
> > ==> build/x86/0x8FD83285_defconfig/log <==
> > drivers/gpu/drm/amd/amdgpu/amdgpu_cs.o: warning: objtool: amdgpu_cs_parser_bos+0x723: unreachable instruction
> > drivers/gpu/drm/xe/xe_bo.o: warning: objtool: xe_bo_create_pin_map_at_novm+0x11d: unreachable instruction
> > drivers/gpu/drm/panthor/panthor_drv.o: warning: objtool: panthor_ioctl_vm_bind+0x2df: unreachable instruction
> 
> These three warnings are accurate, for each of these, Clang is leaving
> an unreachable JMP at the end of the function:
> 
>     166e:	4c 89 ea             	mov    %r13,%rdx
>     1671:	e8 00 00 00 00       	call   1676 <amdgpu_cs_parser_bos+0x716>	1672: R_X86_64_PLT32	__ubsan_handle_shift_out_of_bounds-0x4
>     1676:	49 8b 94 24 08 1d 01 00 	mov    0x11d08(%r12),%rdx
>     167e:	e9 c6 fd ff ff       	jmp    1449 <amdgpu_cs_parser_bos+0x4e9>
>     1683:	e9 8c f9 ff ff       	jmp    1014 <amdgpu_cs_parser_bos+0xb4>
>     1688:	0f 1f 84 00 00 00 00 00 	nopl   0x0(%rax,%rax,1)
> 
> Nathan, any idea?  I haven't seen this pattern before.

This seems pretty similar to

  https://github.com/ClangBuiltLinux/linux/issues/2130
  https://github.com/llvm/llvm-project/issues/167774

as they all use drm_exec_until_all_locked(). Justin fixed this in main
(23.0.0) and it was backported to 22.1.0:

  https://github.com/llvm/llvm-project/commit/404920838836a022b0ae4b9a462befba89ee0cdc
  https://github.com/llvm/llvm-project/commit/2fb8921a7c70b264f670569ac319d1c96e9f5acc

I don't think Arnd has that fix based on the .comment section:

  Debian clang version 22.0.0 (++20251025104945+e219cf60598c-1~exp1~20251025225011.1789)

I don't see a configuration file for these so I cannot verify that they
are actually fixed with a newer version of clang.

Unfortunately, the problematic change landed in the 21.1.0 release so
that version will still see these warnings. I am guessing it is probably
not too easy to workaround this in objtool though, so maybe we will just
have to live with them?

Cheers,
Nathan

Re: clang/objtool failures on linux-next

[Arnd Bergmann]

On Mon, Mar 9, 2026, at 22:15, Nathan Chancellor wrote:
> On Fri, Mar 06, 2026 at 05:35:20PM -0800, Josh Poimboeuf wrote:
>> On Fri, Mar 06, 2026 at 11:04:50PM +0100, Arnd Bergmann wrote:

> I don't think Arnd has that fix based on the .comment section:
>
>   Debian clang version 22.0.0 
> (++20251025104945+e219cf60598c-1~exp1~20251025225011.1789)
>

Correct, I am still using the apt.llvm.org packages on arm64, and
those don't have clang-23 packages yet. I should probably start
using your builds instead.

    Arnd

Re: clang/objtool failures on linux-next

[Arnd Bergmann]

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I've found two more objtool related build failures on today's linux-next.

See attachment for .config and object files.

==> build/x86/0x8F5E6B2F_defconfig/log <==
mm/memory.o: warning: objtool: folio_zero_user+0x69a: undefined stack state
mm/memory.o: error: objtool: folio_zero_user+0x69a: unknown CFA base reg -1
make[5]: *** [/home/arnd/arm-soc/scripts/Makefile.build:279: mm/memory.o] Error 255

==> build/x86/0xEC8A503_defconfig/log <==
vmlinux.o: warning: objtool: ___bpf_prog_run+0x202: sibling call from callable instruction with modified stack frame
vmlinux.o: warning: objtool: __x64_sys_get_mempolicy+0x1705: stack state mismatch: cfa1=4+288 cfa2=4+80
vmlinux.o: error: objtool: vmw_host_printf+0xd: unknown CFA base reg 0
make[4]: *** [/home/arnd/arm-soc/scripts/Makefile.vmlinux_o:76: vmlinux.o] Error 255

       Arnd

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Re: clang/objtool failures on linux-next

[Josh Poimboeuf]

On Mon, Mar 16, 2026 at 10:27:44PM +0100, Arnd Bergmann wrote:
> I've found two more objtool related build failures on today's linux-next.
> 
> See attachment for .config and object files.
> 
> ==> build/x86/0x8F5E6B2F_defconfig/log <==
> mm/memory.o: warning: objtool: folio_zero_user+0x69a: undefined stack state
> mm/memory.o: error: objtool: folio_zero_user+0x69a: unknown CFA base reg -1
> make[5]: *** [/home/arnd/arm-soc/scripts/Makefile.build:279: mm/memory.o] Error 255

This is a clang issue we've seen before, where ASM_CALL_CONSTRAINT
causes clang to save/restore RSP around some inline asm.

The "fix" was going to be asm_call(), as discussed here with Linus:

  https://lore.kernel.org/174099976188.10177.7153571701278544000.tip-bot2@tip-bot2

I need to dust off those patches.

> ==> build/x86/0xEC8A503_defconfig/log <==
> vmlinux.o: warning: objtool: ___bpf_prog_run+0x202: sibling call from callable instruction with modified stack frame
> vmlinux.o: warning: objtool: __x64_sys_get_mempolicy+0x1705: stack state mismatch: cfa1=4+288 cfa2=4+80
> vmlinux.o: error: objtool: vmw_host_printf+0xd: unknown CFA base reg 0
> make[4]: *** [/home/arnd/arm-soc/scripts/Makefile.vmlinux_o:76: vmlinux.o] Error 255

This one's easy, just need to add RAX to the ORC register list.  I will
post a fix shortly.

-- 
Josh