Messages in this thread | | | Subject | Re: [PATCH 3/4] x86/asm/entry/64: use smaller insns | From | "H. Peter Anvin" <> | Date | Wed, 25 Mar 2015 16:56:00 -0700 |
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No, movabs is yet another instruction (with a 64-bit absolute address.) But movq can mean 10 or 7 bytes...
On March 25, 2015 4:51:50 PM PDT, Linus Torvalds <torvalds@linux-foundation.org> wrote: >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
-- Sent from my mobile phone. Please pardon brevity and lack of formatting.
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