Messages in this thread | | | Date | Sat, 12 Mar 2016 18:53:00 +0100 | From | Denys Vlasenko <> | Subject | Re: [PATCH] x86/asm/entry/32: simplify pushes of zeroed pt_regs->REGs |
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On 03/12/2016 04:38 PM, Ingo Molnar wrote: > > * 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)
Yes.
test_syscall_vdso32 checks vdso syscall (if available) and direct int80 syscall. Booting two times, with different qemu flags:
qemu-system-x86_64 -cpu Opteron_G4 qemu-system-x86_64 -cpu SandyBridge
makes kernel choose either SYSCALL or SYSENTER vdso. So it's all covered.
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