Commit 47d2f007 authored by Uros Bizjak's avatar Uros Bizjak Committed by Ingo Molnar
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x86/elf: Use savesegment() for segment register reads in ELF core dump 



ELF_CORE_COPY_REGS() currently reads %ds, %es, %fs, and %gs using
inline assembly and manual zero-extension. This results in redundant
instructions like `mov %eax,%eax`.

Replace the inline assembly with the `savesegment()` helper, which
automatically zero-extends the value to the full register width,
eliminating unnecessary instructions.

For example, the %ds load sequence changes from:

  d03: 8c d8                 mov    %ds,%eax
  d05: 89 c0                 mov    %eax,%eax
  d07: 48 89 84 24 38 01 00  mov    %rax,0x138(%rsp)
  d0e: 00

to:

  ce8: 8c d8                 mov    %ds,%eax
  cea: 48 89 84 24 38 01 00  mov    %rax,0x138(%rsp)
  cf1: 00

thus eliminating the unnecessary zero-extending `mov %eax,%eax`.

No functional change intended.

Signed-off-by: default avatarUros Bizjak <ubizjak@gmail.com>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://patch.msgid.link/20260330085938.67985-1-ubizjak@gmail.com
parent ec631bc3

arch/x86/include/asm/elf.h

+4 −5
Original line number Diff line number Diff line
@@ -187,7 +187,6 @@ void set_personality_ia32(bool); 


#define ELF_CORE_COPY_REGS(pr_reg, regs)			\

do {								\

	unsigned v;						\

	(pr_reg)[0] = (regs)->r15;				\

	(pr_reg)[1] = (regs)->r14;				\

	(pr_reg)[2] = (regs)->r13;				\
@@ -211,10 +210,10 @@ do { \ 
	(pr_reg)[20] = (regs)->ss;				\

	(pr_reg)[21] = x86_fsbase_read_cpu();			\

	(pr_reg)[22] = x86_gsbase_read_cpu_inactive();		\

	asm("movl %%ds,%0" : "=r" (v)); (pr_reg)[23] = v;	\

	asm("movl %%es,%0" : "=r" (v)); (pr_reg)[24] = v;	\

	asm("movl %%fs,%0" : "=r" (v)); (pr_reg)[25] = v;	\

	asm("movl %%gs,%0" : "=r" (v)); (pr_reg)[26] = v;	\

	savesegment(ds, (pr_reg)[23]);				\

	savesegment(es, (pr_reg)[24]);				\

	savesegment(fs, (pr_reg)[25]);				\

	savesegment(gs, (pr_reg)[26]);				\

} while (0);



/* I'm not sure if we can use '-' here */