What's mean lea 0x4(%esp),%ecx in at&t assembly? What really is 0x4(%esp)?
views:
68answers:
3
+2
A:
It's %esp + 0x4.
LEA stands for Load Effective Address. It's, in this case, a simple addition, as shown above. Typically people and compilers don't really use it anymore because CPUs now ship with a nifty address generation unit (otherwise called AGU), which lets you use all kinds of fancy arithmetics to compute addresses from registers and values. In short, whatever you did with lea, you can now embed it inside any other instruction.
zneak
2010-08-13 23:01:46
Uh, `lea` instructions are just under 10% of _all_ instructions generated for the code I happen to be working on right now. It may be true that on x86 you can embed any `lea` operation in a load or store operation (I rather doubt that, honestly), but code is still chock full of pointer arithmetic that doesn't necessarily involve a load or store.
Zack
2010-08-13 23:43:33
I'm not the person who downvoted you, but, um, you know the joke about the helicopter pilot and Microsoft technical support?
Zack
2010-08-13 23:44:59
Jens Björnhager
2010-08-14 13:24:28
+1
A:
esp is the stack pointer. 0x4 is the offset. AT&T syntax has the command source, destination and the command here is LEA which is "Load Effective Address."
So we're telling the CPU to load the address "stack pointer + 4" into the register "ecx"
Computer Guru
2010-08-13 23:13:46