linux-kernel - Re: [PATCH 2/2] x86/purgatory: remove -nostdlib compiler flag

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Date:   Mon, 8 Nov 2021 16:05:31 -0800
From:   Fangrui Song <maskray@...gle.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Masahiro Yamada <masahiroy@...nel.org>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        clang-built-linux@...glegroups.com,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH 2/2] x86/purgatory: remove -nostdlib compiler flag

On 2021-11-08, Nick Desaulniers wrote:
>On Sun, Nov 7, 2021 at 8:27 AM Masahiro Yamada <masahiroy@...nel.org> wrote:
>>
>> The -nostdlib option requests the compiler to not use the standard
>> system startup files or libraries when linking. It is effective only
>> when $(CC) is used as a linker driver.
>
>Is that right? ld.lld recognizes --nostdlib and has --help text for it.

GCC/Clang driver -nostdlib != ld.bfd/ld.lld -nostdlib.

ld.lld -nostdlib just ignores SEARCH_DIR in a linker script.
I think ld.bfd's -nostdlib is more complex than that which also has
something to do with its internal linker script location.
Anyway, getting of the obscure ld -nostdlib is a good idea.

>>
>> $(LD) is directly used for linking purgatory.{ro,chk} here, hence
>> -nostdlib is unneeded.
>>
>> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
>> ---
>>
>>  arch/x86/purgatory/Makefile | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
>> index 95ea17a9d20c..ae53d54d7959 100644
>> --- a/arch/x86/purgatory/Makefile
>> +++ b/arch/x86/purgatory/Makefile
>> @@ -16,7 +16,7 @@ CFLAGS_sha256.o := -D__DISABLE_EXPORTS
>>
>>  # When linking purgatory.ro with -r unresolved symbols are not checked,
>>  # also link a purgatory.chk binary without -r to check for unresolved symbols.
>> -PURGATORY_LDFLAGS := -e purgatory_start -nostdlib -z nodefaultlib
>> +PURGATORY_LDFLAGS := -e purgatory_start -z nodefaultlib
>>  LDFLAGS_purgatory.ro := -r $(PURGATORY_LDFLAGS)
>>  LDFLAGS_purgatory.chk := $(PURGATORY_LDFLAGS)
>>  targets += purgatory.ro purgatory.chk
>> --
>> 2.30.2
>
>-- 
>Thanks,
>~Nick Desaulniers