linux-kernel - [PATCH] x86/boot: Remove x86

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Message-Id: <20221104124546.196077-1-ubizjak@gmail.com>
Date:   Fri,  4 Nov 2022 13:45:46 +0100
From:   Uros Bizjak <ubizjak@...il.com>
To:     x86@...nel.org, linux-kernel@...r.kernel.org
Cc:     Uros Bizjak <ubizjak@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH] x86/boot: Remove x86_32 PIC using ebx workaround

Current minimum required version of GCC is version 5.1 which allows
reuse of PIC hard register on x86/x86-64 targets [1]. Remove
obsolete workaround that was needed for earlier GCC versions.

[1] https://gcc.gnu.org/gcc-5/changes.html

Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Signed-off-by: Uros Bizjak <ubizjak@...il.com>
---
 arch/x86/boot/cpuflags.c | 15 +++------------
 1 file changed, 3 insertions(+), 12 deletions(-)

diff --git a/arch/x86/boot/cpuflags.c b/arch/x86/boot/cpuflags.c
index a83d67ec627d..d75237ba7ce9 100644
--- a/arch/x86/boot/cpuflags.c
+++ b/arch/x86/boot/cpuflags.c
@@ -64,20 +64,11 @@ int has_eflag(unsigned long mask)
 	return !!((f0^f1) & mask);
 }
 
-/* Handle x86_32 PIC using ebx. */
-#if defined(__i386__) && defined(__PIC__)
-# define EBX_REG "=r"
-#else
-# define EBX_REG "=b"
-#endif
-
 void cpuid_count(u32 id, u32 count, u32 *a, u32 *b, u32 *c, u32 *d)
 {
-	asm volatile(".ifnc %%ebx,%3 ; movl  %%ebx,%3 ; .endif	\n\t"
-		     "cpuid					\n\t"
-		     ".ifnc %%ebx,%3 ; xchgl %%ebx,%3 ; .endif	\n\t"
-		    : "=a" (*a), "=c" (*c), "=d" (*d), EBX_REG (*b)
-		    : "a" (id), "c" (count)
+	asm volatile("cpuid"
+		     : "=a" (*a), "=b" (*b), "=c" (*c), "=d" (*d)
+		     : "0" (id), "2" (count)
 	);
 }
 
-- 
2.37.3