Re: [PATCH] export.h: fix section name for CONFIG_TRIM_UNUSED_KSYMS for Clang

[Kees Cook]

On Tue, Sep 29, 2020 at 12:07:00PM -0700, Nick Desaulniers wrote:
> When enabling CONFIG_TRIM_UNUSED_KSYMS, the linker will warn about the
> orphan sections:
> (".discard.ksym") is being placed in '".discard.ksym"'
> repeatedly when linking vmlinux. This is because the stringification
> operator, `#`, in the preprocessor escapes strings.  GCC and Clang
> differ in how they treat section names that contain \".
> 
> The portable solution is to not use a string literal with the
> preprocessor stringification operator.
> 
> Link: https://bugs.llvm.org/show_bug.cgi?id=42950
> Link: https://github.com/ClangBuiltLinux/linux/issues/1166
> Fixes: commit bbda5ec671d3 ("kbuild: simplify dependency generation for CONFIG_TRIM_UNUSED_KSYMS")
> Reported-by: kbuild test robot <lkp@xxxxxxxxx>
> Suggested-by: Kees Cook <keescook@xxxxxxxxxxxx>
> Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>

Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>

Do these other cases need fixing too?

arch/arm64/mm/mmu.c:u64 __section(".mmuoff.data.write") vabits_actual;
include/linux/srcutree.h:               __section("___srcu_struct_ptrs") = &name

-Kees

> ---
>  include/linux/export.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/export.h b/include/linux/export.h
> index fceb5e855717..8933ff6ad23a 100644
> --- a/include/linux/export.h
> +++ b/include/linux/export.h
> @@ -130,7 +130,7 @@ struct kernel_symbol {
>   * discarded in the final link stage.
>   */
>  #define __ksym_marker(sym)	\
> -	static int __ksym_marker_##sym[0] __section(".discard.ksym") __used
> +	static int __ksym_marker_##sym[0] __section(.discard.ksym) __used
>  
>  #define __EXPORT_SYMBOL(sym, sec, ns)					\
>  	__ksym_marker(sym);						\
> -- 
> 2.28.0.709.gb0816b6eb0-goog
> 

-- 
Kees Cook