* Re: [PATCH v4 18/21] compiler.h: RFC - s/__LINE__/__COUNTER__/ in __UNIQUE_ID fallback
2023-07-13 16:36 ` [PATCH v4 18/21] compiler.h: RFC - s/__LINE__/__COUNTER__/ in __UNIQUE_ID fallback Jim Cromie
@ 2023-07-13 17:19 ` Nathan Chancellor
0 siblings, 0 replies; 2+ messages in thread
From: Nathan Chancellor @ 2023-07-13 17:19 UTC (permalink / raw)
To: Jim Cromie
Cc: jbaron, daniel.vetter, linux-kernel, dri-devel, amd-gfx,
intel-gvt-dev, intel-gfx, jani.nikula, ville.syrjala, seanpaul,
robdclark, gregkh, Luc Van Oostenryck, Nick Desaulniers, Tom Rix,
linux-sparse, llvm
Hi Jim
On Thu, Jul 13, 2023 at 10:36:23AM -0600, Jim Cromie wrote:
> We currently have 3 defns for __UNIQUE_ID(); gcc and clang are using
> __COUNTER__ for real uniqueness, 3rd just uses __LINE__, which should
> fail on this (and harder to avoid situations):
>
> DECLARE_FOO(); DECLARE_FOO();
>
> Its 2023, can we haz a no-fallback __UNIQUE_ID ?
Yeah, I fail to see how this fallback definition can actually be used
after commit 95207db8166a ("Remove Intel compiler support"); even before
that, it would be pretty unlikely since icc usage has not been visible
for a long time. The kernel only officially supports clang or GCC now,
so the definitions of __UNIQUE_ID() in include/linux/compiler-clang.h
and include/linux/compiler-gcc.h should always be used because of the
include in include/linux/compiler_types.h, right?
I think the correct clean up is to just hoist the definition of
__UNIQUE_ID() out of the individual compiler headers into the common one
here but...
> NOTE:
>
> This also changes __UNIQUE_ID_ to _kaUID_. Ive been getting
> lkp-reports of collisions on names which should be unique; this
> shouldnt happen on gcc & clang, but does on some older ones, on some
> platforms, on some allyes & rand-configs. Like this:
>
> mips64-linux-ld:
> drivers/gpu/drm/display/drm_dp_helper.o:(__dyndbg_class_users+0x0):
> multiple definition of `__UNIQUE_ID_ddebug_class_user405';
> drivers/gpu/drm/drm_gem_shmem_helper.o:(__dyndbg_class_users+0x0):
> first defined here
This problem cannot be addressed with this patch given the above
information, no? Seems like that might mean that __COUNTER__ has issues
in earlier compilers?
Cheers,
Nathan
> Like above, the collision reports appear to always be 3-digit
> counters, which look like line-numbers. Changing to _kaUID_ in this
> defn should make it more obvious (in *.i file) when a fallback has
> happened. To be clear, I havent seen it yet. Nor have I seen the
> multiple-defn problem above since adding this patch.
>
> Lets see what lkp-robot says about this.
>
> CC: Luc Van Oostenryck <luc.vanoostenryck@gmail.com> (maintainer:SPARSE CHECKER)
> CC: Nathan Chancellor <nathan@kernel.org> (supporter:CLANG/LLVM BUILD SUPPORT)
> CC: Nick Desaulniers <ndesaulniers@google.com> (supporter:CLANG/LLVM BUILD SUPPORT)
> CC: Tom Rix <trix@redhat.com> (reviewer:CLANG/LLVM BUILD SUPPORT)
> CC: linux-sparse@vger.kernel.org (open list:SPARSE CHECKER)
> CC: linux-kernel@vger.kernel.org (open list)
> CC: llvm@lists.linux.dev (open list:CLANG/LLVM BUILD SUPPORT)
> Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
> ---
> include/linux/compiler.h | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> index d7779a18b24f..677d6c47cd9e 100644
> --- a/include/linux/compiler.h
> +++ b/include/linux/compiler.h
> @@ -177,9 +177,9 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
> __asm__ ("" : "=r" (var) : "0" (var))
> #endif
>
> -/* Not-quite-unique ID. */
> +/* JFTI: to fix Not-quite-unique ID */
> #ifndef __UNIQUE_ID
> -# define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __LINE__)
> +# define __UNIQUE_ID(prefix) __PASTE(__PASTE(_kaUID_, prefix), __COUNTER__)
> #endif
>
> /**
> --
> 2.41.0
>
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