[PATCH] x86/percpu: Enable named address spaces for all capable GCC versions

[PATCH] x86/percpu: Enable named address spaces for all capable GCC versions

[Uros Bizjak]

Enable named address spaces also for GCC 6, GCC 7 and GCC 8
releases. These compilers all produce kernel images that boot
without problems.

Use compile-time test to detect compiler support for named
address spaces. The test passes with GCC 6 as the earliest
compiler version where the support for named address spaces
was introduced.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
---
 arch/x86/Kconfig | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 9d16fee6bdb8..c9e0a54f469e 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2430,7 +2430,8 @@ source "kernel/livepatch/Kconfig"
 endmenu
 
 config CC_HAS_NAMED_AS
-	def_bool CC_IS_GCC && GCC_VERSION >= 90100
+	def_bool $(success,echo 'int __seg_fs fs; int __seg_gs gs;' | $(CC) -x c - -S -o /dev/null)
+	depends on CC_IS_GCC
 
 config CC_HAS_NAMED_AS_FIXED_SANITIZERS
 	def_bool CC_IS_GCC && GCC_VERSION >= 130300
-- 
2.45.1

Re: [PATCH] x86/percpu: Enable named address spaces for all capable GCC versions

[Ingo Molnar]

* Uros Bizjak <ubizjak@gmail.com> wrote:

> Enable named address spaces also for GCC 6, GCC 7 and GCC 8
> releases. These compilers all produce kernel images that boot
> without problems.
> 
> Use compile-time test to detect compiler support for named
> address spaces. The test passes with GCC 6 as the earliest
> compiler version where the support for named address spaces
> was introduced.
> 
> Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: Brian Gerst <brgerst@gmail.com>
> Cc: Denys Vlasenko <dvlasenk@redhat.com>
> Cc: H. Peter Anvin <hpa@zytor.com>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Josh Poimboeuf <jpoimboe@redhat.com>
> ---
>  arch/x86/Kconfig | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 9d16fee6bdb8..c9e0a54f469e 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -2430,7 +2430,8 @@ source "kernel/livepatch/Kconfig"
>  endmenu
>  
>  config CC_HAS_NAMED_AS
> -	def_bool CC_IS_GCC && GCC_VERSION >= 90100
> +	def_bool $(success,echo 'int __seg_fs fs; int __seg_gs gs;' | $(CC) -x c - -S -o /dev/null)
> +	depends on CC_IS_GCC

So ... will this test also trigger on Clang, which might have a 
__seg_fs/__seg_gs work-alike definition?

Thanks,

	Ingo

Re: [PATCH] x86/percpu: Enable named address spaces for all capable GCC versions

[Uros Bizjak]

On Tue, May 21, 2024 at 10:18 AM Ingo Molnar <mingo@kernel.org> wrote:
>
>
> * Uros Bizjak <ubizjak@gmail.com> wrote:
>
> > Enable named address spaces also for GCC 6, GCC 7 and GCC 8
> > releases. These compilers all produce kernel images that boot
> > without problems.
> >
> > Use compile-time test to detect compiler support for named
> > address spaces. The test passes with GCC 6 as the earliest
> > compiler version where the support for named address spaces
> > was introduced.
> >
> > Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
> > Cc: Ingo Molnar <mingo@kernel.org>
> > Cc: Andy Lutomirski <luto@kernel.org>
> > Cc: Brian Gerst <brgerst@gmail.com>
> > Cc: Denys Vlasenko <dvlasenk@redhat.com>
> > Cc: H. Peter Anvin <hpa@zytor.com>
> > Cc: Linus Torvalds <torvalds@linux-foundation.org>
> > Cc: Peter Zijlstra <peterz@infradead.org>
> > Cc: Thomas Gleixner <tglx@linutronix.de>
> > Cc: Josh Poimboeuf <jpoimboe@redhat.com>
> > ---
> >  arch/x86/Kconfig | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> > index 9d16fee6bdb8..c9e0a54f469e 100644
> > --- a/arch/x86/Kconfig
> > +++ b/arch/x86/Kconfig
> > @@ -2430,7 +2430,8 @@ source "kernel/livepatch/Kconfig"
> >  endmenu
> >
> >  config CC_HAS_NAMED_AS
> > -     def_bool CC_IS_GCC && GCC_VERSION >= 90100
> > +     def_bool $(success,echo 'int __seg_fs fs; int __seg_gs gs;' | $(CC) -x c - -S -o /dev/null)
> > +     depends on CC_IS_GCC
>
> So ... will this test also trigger on Clang, which might have a
> __seg_fs/__seg_gs work-alike definition?

Yes, but please note the dependence on CC_IS_GCC. This dependence can
be removed once CLANG is tested to create correct code for named AS.

Thanks,
Uros.

[tip: x86/percpu] x86/percpu: Enable named address spaces for all capable GCC versions

[tip-bot2 for Uros Bizjak]

The following commit has been merged into the x86/percpu branch of tip:

Commit-ID:     47ff30cc1be7bf426c03ecc84371452109b416e4
Gitweb:        https://git.kernel.org/tip/47ff30cc1be7bf426c03ecc84371452109b416e4
Author:        Uros Bizjak <ubizjak@gmail.com>
AuthorDate:    Mon, 20 May 2024 10:21:14 +02:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Tue, 21 May 2024 10:17:01 +02:00

x86/percpu: Enable named address spaces for all capable GCC versions

Enable named address spaces also for GCC 6, GCC 7 and GCC 8
releases. These compilers all produce kernel images that boot
without problems.

Use compile-time test to detect compiler support for named
address spaces. The test passes with GCC 6 as the earliest
compiler version where the support for named address spaces
was introduced.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20240520082134.121320-1-ubizjak@gmail.com
---
 arch/x86/Kconfig | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 9d16fee..c9e0a54 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2430,7 +2430,8 @@ source "kernel/livepatch/Kconfig"
 endmenu
 
 config CC_HAS_NAMED_AS
-	def_bool CC_IS_GCC && GCC_VERSION >= 90100
+	def_bool $(success,echo 'int __seg_fs fs; int __seg_gs gs;' | $(CC) -x c - -S -o /dev/null)
+	depends on CC_IS_GCC
 
 config CC_HAS_NAMED_AS_FIXED_SANITIZERS
 	def_bool CC_IS_GCC && GCC_VERSION >= 130300