[PATCH] x86/kexec: store segment registers directly to memory in crash_setup_regs()

[PATCH] x86/kexec: store segment registers directly to memory in crash_setup_regs()

[Uros Bizjak]

crash_setup_regs() currently moves segment registers (ss, cs, ds, es)
into pt_regs via a general purpose register (%eax). Update the code to
avoid the intermediate register and store segment registers directly
to their destination fields. This reduces the generated code from:

 131:	8c d0                	mov    %ss,%eax
 133:	66 89 84 24 a0 00 00 	mov    %ax,0xa0(%rsp)
 13a:	00
 13b:	8c c8                	mov    %cs,%eax
 13d:	66 89 84 24 88 00 00 	mov    %ax,0x88(%rsp)
 144:	00

to:

 131:	8c 94 24 a0 00 00 00 	mov    %ss,0xa0(%rsp)
 138:	8c 8c 24 88 00 00 00 	mov    %cs,0x88(%rsp)

No functional change intended.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Thomas Gleixner <tglx@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
---
 arch/x86/include/asm/kexec.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/kexec.h b/arch/x86/include/asm/kexec.h
index 5cfb27f26583..ad7ef567452b 100644
--- a/arch/x86/include/asm/kexec.h
+++ b/arch/x86/include/asm/kexec.h
@@ -106,11 +106,11 @@ static inline void crash_setup_regs(struct pt_regs *newregs,
 		asm volatile("mov %%r14,%0" : "=m"(newregs->r14));
 		asm volatile("mov %%r15,%0" : "=m"(newregs->r15));
 #endif
-		asm volatile("mov %%ss,%k0" : "=a"(newregs->ss));
-		asm volatile("mov %%cs,%k0" : "=a"(newregs->cs));
+		asm volatile("mov %%ss,%0" : "=m"(newregs->ss));
+		asm volatile("mov %%cs,%0" : "=m"(newregs->cs));
 #ifdef CONFIG_X86_32
-		asm volatile("mov %%ds,%k0" : "=a"(newregs->ds));
-		asm volatile("mov %%es,%k0" : "=a"(newregs->es));
+		asm volatile("mov %%ds,%0" : "=m"(newregs->ds));
+		asm volatile("mov %%es,%0" : "=m"(newregs->es));
 #endif
 		asm volatile("pushf\n\t"
 			     "pop %0" : "=m"(newregs->flags));
-- 
2.53.0