linux-kernel - Re: [PATCH] gendwarfksyms: define __GENKSYMS_

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Message-ID: <CAK7LNARR+LZEUuYSe-TaWwsvA_knwUOoDxZsbucK8GkwBJxgmA@mail.gmail.com>
Date: Thu, 20 Mar 2025 23:40:13 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: Ard Biesheuvel <ardb+git@...gle.com>
Cc: linux-kbuild@...r.kernel.org, brgerst@...il.com, x86@...nel.org, 
	nathan@...nel.org, linux-kernel@...r.kernel.org, nogikh@...gle.com, 
	Ard Biesheuvel <ardb@...nel.org>, Sami Tolvanen <samitolvanen@...gle.com>, 
	syzbot+06fd1a3613c50d36129e@...kaller.appspotmail.com
Subject: Re: [PATCH] gendwarfksyms: define __GENKSYMS__ when processing asm-protoypes.h

On Thu, Mar 20, 2025 at 4:08 PM Ard Biesheuvel <ardb+git@...gle.com> wrote:
>
> From: Ard Biesheuvel <ardb@...nel.org>
>
> 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.


Why don't you make it unconditional, then?

diff --git a/arch/x86/include/asm/asm-prototypes.h
b/arch/x86/include/asm/asm-prototypes.h
index 3674006e3974..9fc6f2be663c 100644
--- a/arch/x86/include/asm/asm-prototypes.h
+++ b/arch/x86/include/asm/asm-prototypes.h
@@ -20,6 +20,4 @@
 extern void cmpxchg8b_emu(void);
 #endif

-#if defined(__GENKSYMS__) && defined(CONFIG_STACKPROTECTOR)
 extern unsigned long __ref_stack_chk_guard;
-#endif






>
> 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@...gle.com>
> Reported-by: syzbot+06fd1a3613c50d36129e@...kaller.appspotmail.com
> Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
> ---
>  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);) ; }
>
> --
> 2.49.0.rc1.451.g8f38331e32-goog
>


-- 
Best Regards
Masahiro Yamada