Re: [PATCH] gendwarfksyms: define __GENKSYMS__ when processing asm-protoypes.h

[Sami Tolvanen]

Hi Ard,

On Thu, Mar 20, 2025 at 12:07 AM Ard Biesheuvel <ardb+git@xxxxxxxxxx> wrote:
>
> From: Ard Biesheuvel <ardb@xxxxxxxxxx>
>
> Ensure that __GENKSYMS__ is #define'd when passing asm/asm-prototypes.h
> through the compiler to capture the exported symbols. This ensures that
> exported symbols such as __ref_stack_chk_guard on x86, which is declared
> conditionally, is visible to the tool.
>
> Otherwise, an error such as the below may be raised, breaking the build
> when CONFIG_GENDWARFKSYMS=y
>
>   <stdin>:4:15: error: use of undeclared identifier '__ref_stack_chk_guard'
>
> Cc: Sami Tolvanen <samitolvanen@xxxxxxxxxx>
> Reported-by: syzbot+06fd1a3613c50d36129e@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
> ---
>  scripts/Makefile.build | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index 993708d11874..7855cdc4e763 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -305,6 +305,7 @@ $(obj)/%.rs: $(obj)/%.rs.S FORCE
>  getasmexports =                                                                \
>     { echo "\#include <linux/kernel.h>" ;                               \
>       echo "\#include <linux/string.h>" ;                               \
> +     echo "\#define  __GENKSYMS__" ;                                   \
>       echo "\#include <asm/asm-prototypes.h>" ;                         \
>       $(call getexportsymbols,EXPORT_SYMBOL(\1);) ; }

This works with gendwarfksyms since __GENKSYMS__ is defined after the
EXPORT_SYMBOL() definition, but I'm now getting warnings with
genksyms:

  AS      arch/x86/lib/clear_page_64.o
<stdin>:3:10: warning: "__GENKSYMS__" redefined
<command-line>: note: this is the location of the previous definition

Sami