Messages in this thread | | | Date | Thu, 26 Mar 2015 11:25:31 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH 3/4] x86/asm/entry/64: use smaller insns |
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* Denys Vlasenko <vda.linux@googlemail.com> wrote:
> In my experiment, GAS uses 10-byte insn only for constants which > won't work with 7-byte encoding; or if I explicitly ask for "movabs": > > _start: .globl _start > mov $0x12345678,%edi # 5 bytes > mov $0x12345678,%rdi # 7 bytes > movq $0x12345678,%rdi # 7 bytes > mov $0x80000000,%rdi # 10 bytes > mov $0x123456789,%rdi # 10 bytes > movabs $0x12345678,%rdi # 10 bytes > > > $ gcc -nostartfiles -nostdlib -c z.S && objdump -dr z.o > z.o: file format elf64-x86-64 > Disassembly of section .text: > 0000000000000000 <_start>: > 0: bf 78 56 34 12 mov $0x12345678,%edi > 5: 48 c7 c7 78 56 34 12 mov $0x12345678,%rdi > c: 48 c7 c7 78 56 34 12 mov $0x12345678,%rdi > 13: 48 bf 00 00 00 80 00 movabs $0x80000000,%rdi > 1a: 00 00 00 > 1d: 48 bf 89 67 45 23 01 movabs $0x123456789,%rdi > 24: 00 00 00 > 27: 48 bf 78 56 34 12 00 movabs $0x12345678,%rdi > 2e: 00 00 00
I see, so:
movq $AUDIT_ARCH_X86_64, %rsi
generated a 10-byte MOVABS opcode, while moving into %esi generates the 5-byte 32-bit MOV opcode?
Thanks,
Ingo
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