Re: [PATCH] ALSA: pcm: Revert bufs move in snd_pcm_xfern_frames_ioctl()

[Takashi Iwai <tiwai@suse.de>]

On Wed, 07 Jan 2026 00:08:18 +0100,
Nathan Chancellor wrote:
> 
> When building with clang older than 17 targeting architectures that use
> asm goto for their get_user() and put_user(), such as arm64, after
> commit f3d233daf011 ("ALSA: pcm: Relax __free() variable declarations"),
> there are bogus errors around skipping over a variable declared with the
> cleanup attribute:
> 
>   sound/core/pcm_native.c:3308:6: error: cannot jump from this asm goto statement to one of its possible targets
>           if (put_user(result, &_xfern->result))
>               ^
>   ...
>   arch/arm64/include/asm/uaccess.h:298:2: note: expanded from macro '__put_mem_asm'
>           asm goto(
>           ^
>   sound/core/pcm_native.c:3295:6: note: possible target of asm goto statement
>           if (put_user(0, &_xfern->result))
>               ^
>   ...
>   sound/core/pcm_native.c:3300:8: note: jump exits scope of variable with __attribute__((cleanup))
>           void *bufs __free(kfree) =
>                 ^
> 
> clang-17 fixed a bug in clang's jump scope checker [1] where all labels
> in a function were checked as valid targets for all asm goto instances
> in a function, regardless of whether they were actual targets in a
> paricular asm goto's provided list of labels.
> 
> To workaround this, revert the change done to
> snd_pcm_xfern_frames_ioctl() by commit f3d233daf011 ("ALSA: pcm: Relax
> __free() variable declarations") to avoid a variable declared with
> cleanup from existing between multiple uses of asm goto. There are no
> other uses of cleanup in this function so there should be low risk from
> moving this variable back to the top of the function.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/1886 [1]
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202512190802.i4Jzbcsl-lkp@intel.com/
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>

I hoped that this mess is addressed in the put_user() side, but it
doesn't seem happening, so I took your workaround now.


thanks,

Takashi