From: Uros Bizjak Date: Mon, 30 Mar 2026 08:59:20 +0000 (+0200) Subject: x86/elf: Use savesegment() for segment register reads in ELF core dump X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=47d2f007615ace34c5ec9026cd5f286833c62c1b;p=thirdparty%2Flinux.git 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: Uros Bizjak Signed-off-by: Ingo Molnar Cc: H. Peter Anvin Cc: Linus Torvalds Link: https://patch.msgid.link/20260330085938.67985-1-ubizjak@gmail.com --- diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h index 2ba5f166e58fe..c7f98977663ca 100644 --- a/arch/x86/include/asm/elf.h +++ b/arch/x86/include/asm/elf.h @@ -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 */