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

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

[Ard Biesheuvel]

From: Ard Biesheuvel <ardb@kernel.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.

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@google.com>
Reported-by: syzbot+06fd1a3613c50d36129e@syzkaller.appspotmail.com
Signed-off-by: Ard Biesheuvel <ardb@kernel.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

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

[Ard Biesheuvel]

On Thu, 20 Mar 2025 at 08:08, Ard Biesheuvel <ardb+git@google.com> wrote:
>
> From: Ard Biesheuvel <ardb@kernel.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.
>
> 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@google.com>
> Reported-by: syzbot+06fd1a3613c50d36129e@syzkaller.appspotmail.com
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

Tested-by: syzbot+06fd1a3613c50d36129e@syzkaller.appspotmail.com

https://syzkaller.appspot.com/bug?extid=06fd1a3613c50d36129e

> ---
>  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
>

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

[Masahiro Yamada]

On Thu, Mar 20, 2025 at 4:08 PM Ard Biesheuvel <ardb+git@google.com> wrote:
>
> From: Ard Biesheuvel <ardb@kernel.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@google.com>
> Reported-by: syzbot+06fd1a3613c50d36129e@syzkaller.appspotmail.com
> Signed-off-by: Ard Biesheuvel <ardb@kernel.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

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

[Ard Biesheuvel]

On Thu, 20 Mar 2025 at 15:40, Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> On Thu, Mar 20, 2025 at 4:08 PM Ard Biesheuvel <ardb+git@google.com> wrote:
> >
> > From: Ard Biesheuvel <ardb@kernel.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?
>

Because this symbol is being hidden from the compiler.

Commit 577c134d311b9b has the details.

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@google.com> wrote:
>
> From: Ard Biesheuvel <ardb@kernel.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.
>
> 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@google.com>
> Reported-by: syzbot+06fd1a3613c50d36129e@syzkaller.appspotmail.com
> Signed-off-by: Ard Biesheuvel <ardb@kernel.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);) ; }

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

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

[Ard Biesheuvel]

On Thu, 20 Mar 2025 at 15:48, Sami Tolvanen <samitolvanen@google.com> wrote:
>
> Hi Ard,
>
> On Thu, Mar 20, 2025 at 12:07 AM Ard Biesheuvel <ardb+git@google.com> wrote:
> >
> > From: Ard Biesheuvel <ardb@kernel.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.
> >
> > 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@google.com>
> > Reported-by: syzbot+06fd1a3613c50d36129e@syzkaller.appspotmail.com
> > Signed-off-by: Ard Biesheuvel <ardb@kernel.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);) ; }
>
> 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
>

Oops.

Do you think the fix below should be sufficient?

--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -314,7 +314,7 @@
 else
 cmd_gensymtypes_S =                                                    \
        $(getasmexports) |                                              \
-       $(CPP) -D__GENKSYMS__ $(c_flags) -xc - | $(genksyms)
+       $(CPP) $(c_flags) -xc - | $(genksyms)
 endif # CONFIG_GENDWARFKSYMS

 quiet_cmd_cpp_s_S = CPP $(quiet_modtag) $@

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

[Sami Tolvanen]

On Thu, Mar 20, 2025 at 9:09 AM Ard Biesheuvel <ardb@kernel.org> wrote:
>
> On Thu, 20 Mar 2025 at 15:48, Sami Tolvanen <samitolvanen@google.com> wrote:
> >
> > Hi Ard,
> >
> > On Thu, Mar 20, 2025 at 12:07 AM Ard Biesheuvel <ardb+git@google.com> wrote:
> > >
> > > From: Ard Biesheuvel <ardb@kernel.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.
> > >
> > > 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@google.com>
> > > Reported-by: syzbot+06fd1a3613c50d36129e@syzkaller.appspotmail.com
> > > Signed-off-by: Ard Biesheuvel <ardb@kernel.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);) ; }
> >
> > 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
> >
>
> Oops.
>
> Do you think the fix below should be sufficient?
>
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -314,7 +314,7 @@
>  else
>  cmd_gensymtypes_S =                                                    \
>         $(getasmexports) |                                              \
> -       $(CPP) -D__GENKSYMS__ $(c_flags) -xc - | $(genksyms)
> +       $(CPP) $(c_flags) -xc - | $(genksyms)
>  endif # CONFIG_GENDWARFKSYMS
>
>  quiet_cmd_cpp_s_S = CPP $(quiet_modtag) $@

EXPORT_SYMBOL() has a different definition when __GENKSYMS__ is
defined, so I think with genksyms we actually do need this on the
command line. I suppose you could wrap the getasmexports definition in
#ifndef __GENKSYMS__ to avoid the warning, or just use
__GENDWARFKSYMS__ like you suggested earlier.

Sami

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

[Ard Biesheuvel]

On Thu, 20 Mar 2025 at 17:22, Sami Tolvanen <samitolvanen@google.com> wrote:
>
> On Thu, Mar 20, 2025 at 9:09 AM Ard Biesheuvel <ardb@kernel.org> wrote:
> >
> > On Thu, 20 Mar 2025 at 15:48, Sami Tolvanen <samitolvanen@google.com> wrote:
> > >
> > > Hi Ard,
> > >
> > > On Thu, Mar 20, 2025 at 12:07 AM Ard Biesheuvel <ardb+git@google.com> wrote:
> > > >
> > > > From: Ard Biesheuvel <ardb@kernel.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.
> > > >
> > > > 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@google.com>
> > > > Reported-by: syzbot+06fd1a3613c50d36129e@syzkaller.appspotmail.com
> > > > Signed-off-by: Ard Biesheuvel <ardb@kernel.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);) ; }
> > >
> > > 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
> > >
> >
> > Oops.
> >
> > Do you think the fix below should be sufficient?
> >
> > --- a/scripts/Makefile.build
> > +++ b/scripts/Makefile.build
> > @@ -314,7 +314,7 @@
> >  else
> >  cmd_gensymtypes_S =                                                    \
> >         $(getasmexports) |                                              \
> > -       $(CPP) -D__GENKSYMS__ $(c_flags) -xc - | $(genksyms)
> > +       $(CPP) $(c_flags) -xc - | $(genksyms)
> >  endif # CONFIG_GENDWARFKSYMS
> >
> >  quiet_cmd_cpp_s_S = CPP $(quiet_modtag) $@
>
> EXPORT_SYMBOL() has a different definition when __GENKSYMS__ is
> defined, so I think with genksyms we actually do need this on the
> command line. I suppose you could wrap the getasmexports definition in
> #ifndef __GENKSYMS__ to avoid the warning, or just use
> __GENDWARFKSYMS__ like you suggested earlier.
>

Yeah, on second thought, we could just do what Masahiro suggested, and
drop the conditional from asm/asm-prototypes.h

The issue in question only affects definitions, not declarations, and
so having the declaration visible shouldn't be a problem.

Ingo, mind dropping this patch again? We'll do the below instead (I'll
send out the patch in a minute)


--- a/arch/x86/include/asm/asm-prototypes.h
+++ b/arch/x86/include/asm/asm-prototypes.h
@@ -20,6 +20,6 @@
 extern void cmpxchg8b_emu(void);
 #endif

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

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

[Ingo Molnar]

* Ard Biesheuvel <ardb@kernel.org> wrote:

> On Thu, 20 Mar 2025 at 17:22, Sami Tolvanen <samitolvanen@google.com> wrote:
> >
> > On Thu, Mar 20, 2025 at 9:09 AM Ard Biesheuvel <ardb@kernel.org> wrote:
> > >
> > > On Thu, 20 Mar 2025 at 15:48, Sami Tolvanen <samitolvanen@google.com> wrote:
> > > >
> > > > Hi Ard,
> > > >
> > > > On Thu, Mar 20, 2025 at 12:07 AM Ard Biesheuvel <ardb+git@google.com> wrote:
> > > > >
> > > > > From: Ard Biesheuvel <ardb@kernel.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.
> > > > >
> > > > > 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@google.com>
> > > > > Reported-by: syzbot+06fd1a3613c50d36129e@syzkaller.appspotmail.com
> > > > > Signed-off-by: Ard Biesheuvel <ardb@kernel.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);) ; }
> > > >
> > > > 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
> > > >
> > >
> > > Oops.
> > >
> > > Do you think the fix below should be sufficient?
> > >
> > > --- a/scripts/Makefile.build
> > > +++ b/scripts/Makefile.build
> > > @@ -314,7 +314,7 @@
> > >  else
> > >  cmd_gensymtypes_S =                                                    \
> > >         $(getasmexports) |                                              \
> > > -       $(CPP) -D__GENKSYMS__ $(c_flags) -xc - | $(genksyms)
> > > +       $(CPP) $(c_flags) -xc - | $(genksyms)
> > >  endif # CONFIG_GENDWARFKSYMS
> > >
> > >  quiet_cmd_cpp_s_S = CPP $(quiet_modtag) $@
> >
> > EXPORT_SYMBOL() has a different definition when __GENKSYMS__ is
> > defined, so I think with genksyms we actually do need this on the
> > command line. I suppose you could wrap the getasmexports definition in
> > #ifndef __GENKSYMS__ to avoid the warning, or just use
> > __GENDWARFKSYMS__ like you suggested earlier.
> >
> 
> Yeah, on second thought, we could just do what Masahiro suggested, and
> drop the conditional from asm/asm-prototypes.h
> 
> The issue in question only affects definitions, not declarations, and
> so having the declaration visible shouldn't be a problem.
> 
> Ingo, mind dropping this patch again? We'll do the below instead (I'll
> send out the patch in a minute)

Yeah, done & thanks!

	Ingo