linux-kernel - Re: [PATCH] x86/boot: Mark global variables as static

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Date:   Tue, 12 May 2020 00:12:26 +0100
From:   Mike Lothian <mike@...eburn.co.uk>
To:     Arvind Sankar <nivedita@...m.mit.edu>
Cc:     Ard Biesheuvel <ardb@...nel.org>,
        linux-efi <linux-efi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        X86 ML <x86@...nel.org>
Subject: Re: [PATCH] x86/boot: Mark global variables as static

Feel free to add my tested by


On Mon, 11 May 2020 at 23:58, Arvind Sankar <nivedita@...m.mit.edu> wrote:
>
> Mike Lothian reports that after commit
>   964124a97b97 ("efi/x86: Remove extra headroom for setup block")
> gcc 10.1.0 fails with
>
>   HOSTCC  arch/x86/boot/tools/build
>   /usr/lib/gcc/x86_64-pc-linux-gnu/10.1.0/../../../../x86_64-pc-linux-gnu/bin/ld:
>   error: linker defined: multiple definition of '_end'
>   /usr/lib/gcc/x86_64-pc-linux-gnu/10.1.0/../../../../x86_64-pc-linux-gnu/bin/ld:
>   /tmp/ccEkW0jM.o: previous definition here
>   collect2: error: ld returned 1 exit status
>   make[1]: *** [scripts/Makefile.host:103: arch/x86/boot/tools/build] Error 1
>   make: *** [arch/x86/Makefile:303: bzImage] Error 2
>
> The issue is with the _end variable that was added, to hold the end of
> the compressed kernel from zoffsets.h (ZO__end). The name clashes with
> the linker-defined _end symbol that indicates the end of the build
> program itself.
>
> Even when there is no compile-time error, this causes build to use
> memory past the end of its .bss section.
>
> To solve this, mark _end as static, and for symmetry, mark the rest of
> the variables that keep track of symbols from the compressed kernel as
> static as well.
>
> Fixes: 964124a97b97 ("efi/x86: Remove extra headroom for setup block")
> Signed-off-by: Arvind Sankar <nivedita@...m.mit.edu>
> ---
>  arch/x86/boot/tools/build.c | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/boot/tools/build.c b/arch/x86/boot/tools/build.c
> index 8f8c8e386cea..c8b8c1a8d1fc 100644
> --- a/arch/x86/boot/tools/build.c
> +++ b/arch/x86/boot/tools/build.c
> @@ -59,14 +59,14 @@ u8 buf[SETUP_SECT_MAX*512];
>  #define PECOFF_COMPAT_RESERVE 0x0
>  #endif
>
> -unsigned long efi32_stub_entry;
> -unsigned long efi64_stub_entry;
> -unsigned long efi_pe_entry;
> -unsigned long efi32_pe_entry;
> -unsigned long kernel_info;
> -unsigned long startup_64;
> -unsigned long _ehead;
> -unsigned long _end;
> +static unsigned long efi32_stub_entry;
> +static unsigned long efi64_stub_entry;
> +static unsigned long efi_pe_entry;
> +static unsigned long efi32_pe_entry;
> +static unsigned long kernel_info;
> +static unsigned long startup_64;
> +static unsigned long _ehead;
> +static unsigned long _end;
>
>  /*----------------------------------------------------------------------*/
>
> --
> 2.26.2
>