linux-kernel - Re: [PATCH v1 2/2] selftests/mm: Guard defines from shm

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Date: Wed, 5 Jun 2024 22:52:24 +0000
From: Carlos Llamas <cmllamas@...gle.com>
To: Edward Liaw <edliaw@...gle.com>
Cc: shuah@...nel.org, Nathan Chancellor <nathan@...nel.org>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
	kernel-team@...roid.com, llvm@...ts.linux.dev, linux-mm@...ck.org
Subject: Re: [PATCH v1 2/2] selftests/mm: Guard defines from shm

On Wed, Jun 05, 2024 at 10:36:35PM +0000, Edward Liaw wrote:
> thuge-gen.c defines SHM_HUGE_* macros that are provided by the uapi
> since 4.14. These macros get redefined when compiling with Android's
> bionic because its sys/shm.h will import the uapi definitions.
> 
> However if linux/shm.h is included, with glibc, sys/shm.h will clash on
> some struct definitions:
> 
>   /usr/include/linux/shm.h:26:8: error: redefinition of ‘struct shmid_ds’
>      26 | struct shmid_ds {
>         |        ^~~~~~~~
>   In file included from /usr/include/x86_64-linux-gnu/bits/shm.h:45,
>                    from /usr/include/x86_64-linux-gnu/sys/shm.h:30:
>   /usr/include/x86_64-linux-gnu/bits/types/struct_shmid_ds.h:24:8: note: originally defined here
>      24 | struct shmid_ds
>         |        ^~~~~~~~

I also hit this issue while using bionic. I have a thread reporting this
issue here: https://lore.kernel.org/all/Zl4LC9lTNptB2xTJ@google.com/

According to Andi Kleen, glibc and others should add these defines in
their headers. So it make sense to me that we would need indefs to
prevent a redefine macro issue.

> 
> For now, guard the SHM_HUGE_* defines with ifndef to prevent
> redefinition warnings on Android bionic.
> 
> Signed-off-by: Edward Liaw <edliaw@...gle.com>
> ---
>  tools/testing/selftests/mm/thuge-gen.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/tools/testing/selftests/mm/thuge-gen.c b/tools/testing/selftests/mm/thuge-gen.c
> index 034635317935..d50dc71cac32 100644
> --- a/tools/testing/selftests/mm/thuge-gen.c
> +++ b/tools/testing/selftests/mm/thuge-gen.c
> @@ -34,10 +34,18 @@
>  #endif
>  
>  #define SHM_HUGETLB     04000   /* segment will use huge TLB pages */
> +#ifndef SHM_HUGE_SHIFT

nit: I see this file uses the form "#if !defined()" above for
MAP_HUGETLB. Perhaps it makes sense to use that and keep things
consistent? I'm fine either way.

Reviewed-by: Carlos Llamas <cmllamas@...gle.com>

>  #define SHM_HUGE_SHIFT  26
> +#endif
> +#ifndef SHM_HUGE_MASK
>  #define SHM_HUGE_MASK   0x3f
> +#endif
> +#ifndef SHM_HUGE_2MB
>  #define SHM_HUGE_2MB    (21 << SHM_HUGE_SHIFT)
> +#endif
> +#ifndef SHM_HUGE_1GB
>  #define SHM_HUGE_1GB    (30 << SHM_HUGE_SHIFT)
> +#endif
>  
>  #define NUM_PAGESIZES   5
>  #define NUM_PAGES 4
> -- 
> 2.45.1.467.gbab1589fc0-goog
>