linux-kernel - Re: [PATCH v6 06/10] kbuild: check static EXPORT

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Date:   Tue, 7 Jun 2022 15:34:06 +0100
From:   Jon Hunter <jonathanh@...dia.com>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Schier <nicolas@...sle.eu>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-modules@...r.kernel.org, llvm@...ts.linux.dev,
        Ard Biesheuvel <ardb@...nel.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH v6 06/10] kbuild: check static EXPORT_SYMBOL* by script
 instead of modpost


On 07/06/2022 15:25, Nathan Chancellor wrote:
> On Tue, Jun 07, 2022 at 03:22:21PM +0100, Jon Hunter wrote:
>>
>> 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@...nel.org>
>>> Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
>>> Tested-by: Nathan Chancellor <nathan@...nel.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?
> 
> https://lore.kernel.org/20220607084317.211785-1-masahiroy@kernel.org/
> should resolve it if you wanted to give it a test.

Thanks! Works for me.

Tested-by: Jon Hunter <jonathanh@...dia.com>

Cheers
Jon

-- 
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