Commit-ID: 7a5a9824c18f93415944c997dc6bb8eecfddd2e7 Gitweb: http://git.kernel.org/tip/7a5a9824c18f93415944c997dc6bb8eecfddd2e7 Author: Denys Vlasenko <dvlasenk@xxxxxxxxxx> AuthorDate: Wed, 3 Jun 2015 15:58:50 +0200 Committer: Ingo Molnar <mingo@xxxxxxxxxx> CommitDate: Fri, 5 Jun 2015 13:41:28 +0200 x86/asm/entry/32: Remove unnecessary optimization in stub32_clone Really swap arguments #4 and #5 in stub32_clone instead of "optimizing" it into a move. Yes, tls_val is currently unused. Yes, on some CPUs XCHG is a little bit more expensive than MOV. But a cycle or two on an expensive syscall like clone() is way below noise floor, and this optimization is simply not worth the obfuscation of logic. [ There's also ongoing work on the clone() ABI by Josh Triplett that will depend on this change later on. ] Signed-off-by: Denys Vlasenko <dvlasenk@xxxxxxxxxx> Cc: Alexei Starovoitov <ast@xxxxxxxxxxxx> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx> Cc: Borislav Petkov <bp@xxxxxxxxx> Cc: Brian Gerst <brgerst@xxxxxxxxx> Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx> Cc: H. Peter Anvin <hpa@xxxxxxxxx> Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx> Cc: Kees Cook <keescook@xxxxxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Oleg Nesterov <oleg@xxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Will Drewry <wad@xxxxxxxxxxxx> Link: http://lkml.kernel.org/r/1433339930-20880-2-git-send-email-dvlasenk@xxxxxxxxxx Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> --- arch/x86/entry/ia32entry.S | 13 ++++++------- 1 file changed, 6 insertions(+), 7 deletions(-) diff --git a/arch/x86/entry/ia32entry.S b/arch/x86/entry/ia32entry.S index d0c7b28..9558dac 100644 --- a/arch/x86/entry/ia32entry.S +++ b/arch/x86/entry/ia32entry.S @@ -529,14 +529,13 @@ GLOBAL(\label) GLOBAL(stub32_clone) leaq sys_clone(%rip), %rax /* - * 32-bit clone API is clone(..., int tls_val, int *child_tidptr). - * 64-bit clone API is clone(..., int *child_tidptr, int tls_val). - * Native 64-bit kernel's sys_clone() implements the latter. - * We need to swap args here. But since tls_val is in fact ignored - * by sys_clone(), we can get away with an assignment - * (arg4 = arg5) instead of a full swap: + * The 32-bit clone ABI is: clone(..., int tls_val, int *child_tidptr). + * The 64-bit clone ABI is: clone(..., int *child_tidptr, int tls_val). + * + * The native 64-bit kernel's sys_clone() implements the latter, + * so we need to swap arguments here before calling it: */ - mov %r8, %rcx + xchg %r8, %rcx jmp ia32_ptregs_common ALIGN -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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