Messages in this thread | | | Date | Wed, 25 Mar 2015 16:51:50 -0700 | Subject | Re: [PATCH 3/4] x86/asm/entry/64: use smaller insns | From | Linus Torvalds <> |
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On Wed, Mar 25, 2015 at 10:18 AM, Denys Vlasenko <dvlasenk@redhat.com> wrote: > The $AUDIT_ARCH_X86_64 parameter to syscall_trace_enter_phase1/2 > is a 32-bit constant, loading it with 32-bit MOV produces 5-byte insn > instead of 10-byte one.
Side note: has anybody talked to the assembler people? This would seem to be very much something that the assembler could have noticed and done on its own. It's a bit sad that we need to overspecify these things..
If it had actually been a 64-bit constant, the assembler would have ended up silently using a different instruction encoding *anyway* ("movabs"), so it's not like the "movq" in any way specifies one particular instruction representation, and the assembler already picks different instruction versions for different constant values. Why not this one?
Linus
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