Re: [PATCH v6 06/10] kbuild: check static EXPORT_SYMBOL* by script instead of modpost

From: Jon Hunter <jonathanh@nvidia.com>
To: Masahiro Yamada <masahiroy@kernel.org>, linux-kbuild@vger.kernel.org
Cc: linux-kernel@vger.kernel.org,
	Nathan Chancellor <nathan@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Nicolas Schier <nicolas@fjasle.eu>,
	Peter Zijlstra <peterz@infradead.org>,
	linux-modules@vger.kernel.org, llvm@lists.linux.dev,
	Ard Biesheuvel <ardb@kernel.org>,
	Sami Tolvanen <samitolvanen@google.com>,
	"linux-tegra@vger.kernel.org" <linux-tegra@vger.kernel.org>
Subject: Re: [PATCH v6 06/10] kbuild: check static EXPORT_SYMBOL* by script instead of modpost
Date: Tue, 7 Jun 2022 15:22:21 +0100	[thread overview]
Message-ID: <e020f60d-218c-8e47-5863-23dcb55452f2@nvidia.com> (raw)
In-Reply-To: <20220513113930.10488-7-masahiroy@kernel.org>

On 13/05/2022 12:39, Masahiro Yamada wrote:
> The 'static' specifier and EXPORT_SYMBOL() are an odd combination.
> 
> Commit 15bfc2348d54 ("modpost: check for static EXPORT_SYMBOL*
> functions") tried to detect it, but this check has false negatives.
> 
> Here is the sample code.
> 
>    Makefile:
> 
>      obj-y += foo1.o foo2.o
> 
>    foo1.c:
> 
>      #include <linux/export.h>
>      static void foo(void) {}
>      EXPORT_SYMBOL(foo);
> 
>    foo2.c:
> 
>      void foo(void) {}
> 
> foo1.c exports the static symbol 'foo', but modpost cannot catch it
> because it is fooled by foo2.c, which has a global symbol with the
> same name.
> 
> s->is_static is cleared if a global symbol with the same name is found
> somewhere, but EXPORT_SYMBOL() and the global symbol do not necessarily
> belong to the same compilation unit.
> 
> This check should be done per compilation unit, but I do not know how
> to do it in modpost. modpost runs against vmlinux.o or modules, which
> merges multiple objects, then forgets their origin.
> 
> It is true modpost gets access to the lists of all the member objects
> (.vmlinux.objs and *.mod), but modpost cannot parse individual objects
> because they may not be ELF but LLVM IR when CONFIG_LTO_CLANG=y.
> 
> Add a simple bash script to parse the output from ${NM}. This works for
> CONFIG_LTO_CLANG=y because llvm-nm can dump symbols of LLVM IR files.
> 
> Revert 15bfc2348d54.
> 
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
> Tested-by: Nathan Chancellor <nathan@kernel.org>

One some older build machines this is causing some builds (ARM/ARM64)
to fail ...

/dvs/git/dirty/git-master_l4t-upstream/kernel/scripts/check-local-export: line 54: wait: pid 48433 is not a child of this shell
/dvs/git/dirty/git-master_l4t-upstream/kernel/scripts/Makefile.build:250: recipe for target 'scripts/mod/empty.o' failed
make[2]: *** [scripts/mod/empty.o] Error 127
make[2]: *** Deleting file 'scripts/mod/empty.o'
make[2]: *** Waiting for unfinished jobs....
/dvs/git/dirty/git-master_l4t-upstream/kernel/Makefile:1285: recipe for target 'prepare0' failed
make[1]: *** [prepare0] Error 2
make[1]: Leaving directory '/dvs/git/dirty/git-master_l4t-upstream/artifacts/linux/arm64-defconfig-jetson'
Makefile:228: recipe for target '__sub-make' failed
make: *** [__sub-make] Error 2

Any ideas?

Thanks
Jon

-- 
nvpublic