On Thu, Mar 26, 2015 at 11:25 AM, Ingo Molnar <mi...@kernel.org> wrote: > * Denys Vlasenko <vda.li...@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?
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