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

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Nick Desaulniers

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Sep 29, 2020, 3:07:20 PM9/29/20
to Andrew Morton, Nick Desaulniers, kbuild test robot, Kees Cook, Nathan Chancellor, Masahiro Yamada, Matthias Maennich, Jessica Yu, Greg Kroah-Hartman, Will Deacon, linux-...@vger.kernel.org, clang-bu...@googlegroups.com
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 <l...@intel.com>
Suggested-by: Kees Cook <kees...@chromium.org>
Signed-off-by: Nick Desaulniers <ndesau...@google.com>
---
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

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Sep 29, 2020, 7:44:28 PM9/29/20
to Nick Desaulniers, Andrew Morton, kbuild test robot, Nathan Chancellor, Masahiro Yamada, Matthias Maennich, Jessica Yu, Greg Kroah-Hartman, Will Deacon, linux-...@vger.kernel.org, clang-bu...@googlegroups.com
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 <l...@intel.com>
> Suggested-by: Kees Cook <kees...@chromium.org>
> Signed-off-by: Nick Desaulniers <ndesau...@google.com>

Reviewed-by: Kees Cook <kees...@chromium.org>

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

Nathan Chancellor

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Sep 30, 2020, 12:26:43 PM9/30/20
to Nick Desaulniers, Andrew Morton, kbuild test robot, Kees Cook, Masahiro Yamada, Matthias Maennich, Jessica Yu, Greg Kroah-Hartman, Will Deacon, linux-...@vger.kernel.org, clang-bu...@googlegroups.com
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 <l...@intel.com>
> Suggested-by: Kees Cook <kees...@chromium.org>
> Signed-off-by: Nick Desaulniers <ndesau...@google.com>

Reviewed-by: Nathan Chancellor <natecha...@gmail.com>

Sedat Dilek

unread,
Sep 30, 2020, 12:43:45 PM9/30/20
to Nick Desaulniers, Andrew Morton, kbuild test robot, Kees Cook, Nathan Chancellor, Masahiro Yamada, Matthias Maennich, Jessica Yu, Greg Kroah-Hartman, Will Deacon, linux-...@vger.kernel.org, Clang-Built-Linux ML
On Tue, Sep 29, 2020 at 9:07 PM 'Nick Desaulniers' via Clang Built
Linux <clang-bu...@googlegroups.com> 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 <l...@intel.com>
> Suggested-by: Kees Cook <kees...@chromium.org>
> Signed-off-by: Nick Desaulniers <ndesau...@google.com>

"The return of escaped section names" - soon in your cinema?

Thanks Nick for catching this.

Reviewed-by: Sedat Dilek <sedat...@gmail.com>

- Sedat -

> ---
> 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
>
> --
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