linux-kernel - Re: [syzbot] linux-next build error (20)

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Message-ID: <CABCJKuednNrveGz6tQqHj7bbnVzLJFgCLt0CuZLT2KOvt8aNrg@mail.gmail.com>
Date: Wed, 19 Mar 2025 18:45:16 +0000
From: Sami Tolvanen <samitolvanen@...gle.com>
To: Ard Biesheuvel <ardb@...nel.org>
Cc: Aleksandr Nogikh <nogikh@...gle.com>, Masahiro Yamada <masahiroy@...nel.org>, 
	syzbot <syzbot+06fd1a3613c50d36129e@...kaller.appspotmail.com>, brgerst@...il.com, 
	linux-kernel@...r.kernel.org, linux-next@...r.kernel.org, 
	sfr@...b.auug.org.au, syzkaller-bugs@...glegroups.com, 
	Dmitry Vyukov <dvyukov@...gle.com>, Ingo Molnar <mingo@...nel.org>
Subject: Re: [syzbot] linux-next build error (20)

Hi Ard,

On Wed, Mar 19, 2025 at 8:38 AM Ard Biesheuvel <ardb@...nel.org> wrote:
>
> The issue here is that we deliberately hide __ref_stack_chk_guard from
> the compiler, because Clang will otherwise generate incorrect code.
> [0]
>
> I managed to work around this issue using the hack below, but I'm not
> too familiar with the gendwarfksyms code, so I'll leave it up to Sami
> and Masahiro to decide whether this is the right approach before
> sending out a patch.
>
>
> --- a/arch/x86/include/asm/asm-prototypes.h
> +++ b/arch/x86/include/asm/asm-prototypes.h
> @@ -20,6 +20,7 @@
>  extern void cmpxchg8b_emu(void);
>  #endif
>
> -#if defined(__GENKSYMS__) && defined(CONFIG_STACKPROTECTOR)
> +#if (defined(__GENKSYMS__) || defined(__GENDWARFKSYMS__)) \
> +       && defined(CONFIG_STACKPROTECTOR)
>  extern unsigned long __ref_stack_chk_guard;
>  #endif
>
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -311,7 +311,8 @@
>  ifdef CONFIG_GENDWARFKSYMS
>  cmd_gensymtypes_S =                                                    \
>         $(getasmexports) |                                              \
> -       $(CC) $(c_flags) -c -o $(@:.o=.gendwarfksyms.o) -xc -;          \
> +       $(CC) -D__GENDWARFKSYMS__                                       \
> +               $(c_flags) -c -o $(@:.o=.gendwarfksyms.o) -xc -;        \
>         $(call getexportsymbols,\1) |                                   \
>         $(gendwarfksyms) $(@:.o=.gendwarfksyms.o)
>  else

The patch looks reasonable to me. Thanks for figuring this out!

Sami