From a7bea8308933aaeea76dad7d42a6e51000417626 Mon Sep 17 00:00:00 2001 From: Jan Beulich Date: Mon, 2 Jul 2018 04:31:54 -0600 Subject: x86/asm/64: Use 32-bit XOR to zero registers Some Intel CPUs don't recognize 64-bit XORs as zeroing idioms. Zeroing idioms don't require execution bandwidth, as they're being taken care of in the frontend (through register renaming). Use 32-bit XORs instead. Signed-off-by: Jan Beulich Cc: Alok Kataria Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Josh Poimboeuf Cc: Juergen Gross Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: davem@davemloft.net Cc: herbert@gondor.apana.org.au Cc: pavel@ucw.cz Cc: rjw@rjwysocki.net Link: http://lkml.kernel.org/r/5B39FF1A02000078001CFB54@prv1-mh.provo.novell.com Signed-off-by: Ingo Molnar --- arch/x86/kernel/head_64.S | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'arch/x86/kernel/head_64.S') diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S index 8344dd2f310a..15ebc2fc166e 100644 --- a/arch/x86/kernel/head_64.S +++ b/arch/x86/kernel/head_64.S @@ -235,7 +235,7 @@ ENTRY(secondary_startup_64) * address given in m16:64. */ pushq $.Lafter_lret # put return address on stack for unwinder - xorq %rbp, %rbp # clear frame pointer + xorl %ebp, %ebp # clear frame pointer movq initial_code(%rip), %rax pushq $__KERNEL_CS # set correct cs pushq %rax # target address in negative space -- cgit v1.2.3