[PATCH] kbuild: linker script do not match C names unless LD_DEAD_CODE_DATA_ELIMINATION is configured

[Masahiro Yamada]

Hi Nicholas,

2017-07-26 21:46 GMT+09:00 Nicholas Piggin <npiggin at gmail.com>:
> The .data and .bss sections were modified in the generic linker script to
> pull in sections named .data.<C identifier>, which are generated by gcc with
> -ffunction-sections and -fdata-sections options.
>
> The problem with this pattern is it can also match section names that Linux
> defines explicitly, e.g., .data.unlikely. This can cause Linux sections to
> get moved into the wrong place.
>
> The way to avoid this is to use ".." separators for explicit section names
> (the dot character is valid in a section name but not a C identifier).
> However currently there are sections which don't follow this rule, so for
> now just disable the wild card by default.
>
> Example: http://marc.info/?l=linux-arm-kernel&m=150106824024221&w=2
>
> Cc: <stable at vger.kernel.org> # 4.9
> Fixes: b67067f1176df ("kbuild: allow archs to select link dead code/data elimination")
> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
> ---
>  include/asm-generic/vmlinux.lds.h | 38 ++++++++++++++++++++++++++------------
>  1 file changed, 26 insertions(+), 12 deletions(-)
>
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index da0be9a8d1de..9623d78f8494 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -60,6 +60,22 @@
>  #define ALIGN_FUNCTION()  . = ALIGN(8)
>
>  /*
> + * LD_DEAD_CODE_DATA_ELIMINATION option enables -fdata-sections, which
> + * generates .data.identifier sections, which need to be pulled in with
> + * .data. We don't want to pull in .data..other sections, which Linux
> + * has defined. Same for text and bss.
> + */
> +#ifdef CONFIG_LD_DEAD_CODE_DATA_ELIMINATION
> +#define TEXT_MAIN .text .text.[0-9a-zA-Z_]*
> +#define DATA_MAIN .data .data.[0-9a-zA-Z_]*
> +#define BSS_MAIN .bss .bss.[0-9a-zA-Z_]*
> +#else
> +#define TEXT_MAIN .text
> +#define DATA_MAIN .data
> +#define BSS_MAIN .bss
> +#endif


>From the git-log, I think you are planning to rename
  .data.unlikely   ->   .data..unlikey
then the problem will be fixed.

("git grep data.unlikely" gave me only 7 instances.)


Why is this patch necessary?


You are trying to migrate some architectures to DCDE,
so this #ifdef does not solve the problem, I think.






-- 
Best Regards
Masahiro Yamada