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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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[PATCH] x86/asm/entry/32: simplify pushes of zeroed pt_regs->REGs Denys Vlasenko <dvlasenk@redhat.com> - 2016-03-11 18:00 +0100
  Re: [PATCH] x86/asm/entry/32: simplify pushes of zeroed pt_regs->REGs Ingo Molnar <mingo@kernel.org> - 2016-03-12 16:40 +0100
    Re: [PATCH] x86/asm/entry/32: simplify pushes of zeroed pt_regs->REGs Denys Vlasenko <dvlasenk@redhat.com> - 2016-03-12 19:00 +0100
      Re: [PATCH] x86/asm/entry/32: simplify pushes of zeroed pt_regs->REGs Andy Lutomirski <luto@amacapital.net> - 2016-03-12 19:10 +0100
        Re: [PATCH] x86/asm/entry/32: simplify pushes of zeroed pt_regs->REGs Denys Vlasenko <dvlasenk@redhat.com> - 2016-03-12 22:50 +0100
  Re: [PATCH] x86/asm/entry/32: simplify pushes of zeroed pt_regs->REGs Ingo Molnar <mingo@kernel.org> - 2016-03-12 16:50 +0100

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