Hi, These two instructions are equivalent:
movq $0x12345678, %rax movl $0x12345678, %eax But gas (2.17.50.0.12 on Fedora 7) chooses a longer encoding for the former: 22: 48 c7 c0 78 56 34 12 mov $0x12345678,%rax 29: b8 78 56 34 12 mov $0x12345678,%eax In fact, for any non-negative immediate constant that fits in 32 bits, it's better to use the "mov imm32, r32" instruction (0xb8), rather than "mov imm32, r64" (REX 0xc7). Negative constants need the sign-extending effect of REX 0xc7. gcc-generated assembly doesn't seem to run into this, but hand-coded assembly often does (see for example the x86-64 Linux kernel). David Wragg _______________________________________________ bug-binutils mailing list bug-binutils@gnu.org http://lists.gnu.org/mailman/listinfo/bug-binutils
