2020年12月9日 · The compiler could have moved this load earlier as well, but chose not to. But add %dl, (%rax) is an RMW on (%rax), so the dl data isn't needed until a load from (%rax) has …

See the question and answer for x86_64 registers rax/eax/ax/al overwriting full register contents as well as Why do most x64 instructions zero the upper part of a 32 bit register which provide …

2016年12月20日 · mov %rax, %eax # AT&T syntax (INVALID!) mov eax, rax ; Intel syntax (INVALID!) but not identical. This last case is actually an invalid instruction because there is an …

2013年12月13日 · uint64_t rax = 0, rbx = 0; __asm__("" : "=a"(rax), "=b"(rbx) ::); /* make rax and rbx take on the current values in those registers */ Note that you don't need any actual …

2017年7月7日 · The registers starting with r as in rax, rbx, etc, are the 64-bit registers introduced with the AMD64 extension to the existing 32-bit x86 ISA. That ISA extension was subsequently …

2019年7月10日 · You’re right that there appears to be an extra level of indirection here, since (%rax) already indicates the memory at the address contained in rax. The asterisk is an …

hmm eax == 32bits ax == 16bits ah|al == 8bits, it's always like this, x64 adds new registers, back in the 16 bit days we only had ax & al & ah then when 32 bit addressing came round it was …

2021年6月28日 · Remember that the RAX return-value register isn't written by the function until after you've jumped to it, so yes of course it's fine to use RAX as a temporary before a tailcall, …

I asked about reading those registers. Now I wrote a code to read (just for now on) RAX and RBX. I'm using CodeBlocks pm 64-bit Windows 7 with MinGW as a compiler and I'm working on an …

2012年11月24日 · In the following: #include <string.h> struct cpuidOut { long a ; long b ; long c ; long d ; } ; void callcpuid( cpuidOut * p, long a ) { memset( p, 0xFF, sizeof(*p ...