linux-kernel - [RFC PATCH 2/4] x86/percpu: Detect compiler support for named address spaces

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Message-ID: <20231001131620.112484-3-ubizjak@gmail.com>
Date:   Sun,  1 Oct 2023 15:14:34 +0200
From:   Uros Bizjak <ubizjak@...il.com>
To:     x86@...nel.org, linux-kernel@...r.kernel.org
Cc:     Uros Bizjak <ubizjak@...il.com>, Andy Lutomirski <luto@...nel.org>,
        Ingo Molnar <mingo@...nel.org>, Nadav Amit <namit@...are.com>,
        Brian Gerst <brgerst@...il.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: [RFC PATCH 2/4] x86/percpu: Detect compiler support for named address spaces

Detect compiler support for named address spaces by trying
to compile a small testcase that includes __seg_gs and __seg_gs
keywords. Reflect successful compilation in CC_HAS_NAMED_AS
and set USE_X86_SEG_SUPPORT to signal when segment qualifiers
should be used.

Cc: Andy Lutomirski <luto@...nel.org>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Nadav Amit <namit@...are.com>
Cc: Brian Gerst <brgerst@...il.com>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Signed-off-by: Uros Bizjak <ubizjak@...il.com>
---
 arch/x86/Kconfig | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 66bfabae8814..f66fa5bf1f78 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2388,6 +2388,13 @@ source "kernel/livepatch/Kconfig"
 
 endmenu
 
+config CC_HAS_NAMED_AS
+	def_bool $(success,echo 'int __seg_fs fs; int __seg_gs gs;' | $(CC) -x c - -c -o /dev/null)
+
+config USE_X86_SEG_SUPPORT
+	def_bool y
+	depends on CC_HAS_NAMED_AS && SMP
+
 config CC_HAS_SLS
 	def_bool $(cc-option,-mharden-sls=all)
 
-- 
2.41.0