On Wed, Apr 22, 2015 at 9:40 AM, Denys Vlasenko <dvlas...@redhat.com> wrote: > 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 obfuscation of logic introduced > by this optimization is simply not worth it.
Ditto re: Josh's patch. --Andy > > Signed-off-by: Denys Vlasenko <dvlas...@redhat.com> > CC: Linus Torvalds <torva...@linux-foundation.org> > CC: Steven Rostedt <rost...@goodmis.org> > CC: Ingo Molnar <mi...@kernel.org> > CC: Borislav Petkov <b...@alien8.de> > CC: "H. Peter Anvin" <h...@zytor.com> > CC: Andy Lutomirski <l...@amacapital.net> > CC: Oleg Nesterov <o...@redhat.com> > CC: Frederic Weisbecker <fweis...@gmail.com> > CC: Alexei Starovoitov <a...@plumgrid.com> > CC: Will Drewry <w...@chromium.org> > CC: Kees Cook <keesc...@chromium.org> > CC: x...@kernel.org > CC: linux-kernel@vger.kernel.org > --- > arch/x86/ia32/ia32entry.S | 6 ++---- > 1 file changed, 2 insertions(+), 4 deletions(-) > > diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S > index 8e72256..0c302d0 100644 > --- a/arch/x86/ia32/ia32entry.S > +++ b/arch/x86/ia32/ia32entry.S > @@ -567,11 +567,9 @@ GLOBAL(stub32_clone) > * 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: > + * We need to swap args here: > */ > - mov %r8, %rcx > + xchg %r8, %rcx > jmp ia32_ptregs_common > > ALIGN > -- > 1.8.1.4 > -- Andy Lutomirski AMA Capital Management, LLC -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
