linux-kernel - Re: [PATCH] x86, realmode: explicitly set ENTRY in linker script

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Date:   Tue, 24 Sep 2019 11:24:17 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        clang-built-linux@...glegroups.com,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86, realmode: explicitly set ENTRY in linker script

On Mon, Sep 23, 2019 at 03:24:02PM -0700, 'Nick Desaulniers' via Clang Built Linux wrote:
> Linking with ld.lld via $ make LD=ld.lld produces the warning:
> ld.lld: warning: cannot find entry symbol _start; defaulting to 0x1000
> 
> Linking with ld.bfd shows the default entry is 0x1000:
> $ readelf -h arch/x86/realmode/rm/realmode.elf | grep Entry
>   Entry point address:               0x1000
> 
> While ld.lld is being pedantic, just set the entry point explicitly,
> instead of depending on the implicit default.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/216
> Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
> ---
>  arch/x86/realmode/rm/realmode.lds.S | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/x86/realmode/rm/realmode.lds.S b/arch/x86/realmode/rm/realmode.lds.S
> index 3bb980800c58..2034f5f79bff 100644
> --- a/arch/x86/realmode/rm/realmode.lds.S
> +++ b/arch/x86/realmode/rm/realmode.lds.S
> @@ -11,6 +11,7 @@
>  
>  OUTPUT_FORMAT("elf32-i386")
>  OUTPUT_ARCH(i386)
> +ENTRY(0x1000)
>  
>  SECTIONS
>  {
> -- 
> 2.23.0.351.gc4317032e6-goog
> 

This appears to break ld.bfd?

ld:arch/x86/realmode/rm/realmode.lds:131: syntax error
make[5]: *** [../arch/x86/realmode/rm/Makefile:54: arch/x86/realmode/rm/realmode.elf] Error 1
make[4]: *** [../arch/x86/realmode/Makefile:20: arch/x86/realmode/rm/realmode.bin] Error 2
make[3]: *** [../scripts/Makefile.build:509: arch/x86/realmode] Error 2

Cheers,
Nathan