Messages in this thread | | | Date | Sat, 12 Mar 2016 16:38:08 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH] x86/asm/entry/32: simplify pushes of zeroed pt_regs->REGs |
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* Denys Vlasenko <dvlasenk@redhat.com> wrote:
> Use of a temporary R8 register here seems to be unnecessary. > > "push %r8" is a two-byte insn (it needs REX prefix to specify R8), > "push $0" is two-byte too. It seems just using the latter would be > no worse. > > Thus, code had an unnecessary "xorq %r8,%r8" insn.
Neat!
> It probably costs nothing in execution time here since we are probably > limited by store bandwidth at this point, but still. > > Run-tested under QEMU: 32-bit calls still work: > > / # ./test_syscall_vdso32
Did you manage to test all 3 compat variants:
> @@ -72,24 +72,23 @@ ENTRY(entry_SYSENTER_compat) > @@ -205,17 +204,16 @@ ENTRY(entry_SYSCALL_compat) > @@ -316,11 +314,10 @@ ENTRY(entry_INT80_compat)
?
Thanks,
Ingo
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