I'm having some really big problems trying to get certain x86 instructions assembled properly using .intel_syntax, compiling with -m32 (i.e. 32-bit mode). If I have some code like this:
#define STACK_SIZE 0x4000
.att_syntax
movl $(stack + STACK_SIZE), %esp
.comm stack, STACK_SIZE
...all is fine. The decompiled output from this looks like this (AT&T syntax first, Intel syntax shown afterwards).
100010: bc 70 5a 10 00 mov $0x105a70,%esp
100010: bc 70 5a 10 00 mov esp,0x105a70
However, if I change my code like this (which I feel "should" work):
.intel_syntax noprefix
mov esp, stack + STACK_SIZE
...I get this output instead:
100010: 8b 25 70 5a 10 00 mov 0x105a70,%esp
100010: 8b 25 70 5a 10 00 mov esp,DWORD PTR ds:0x105a70
Obviously, this is wrong; I'm not trying to dereference the stack label but instead create a reference to it.
For now, my workaround is to use AT&T syntax for some parts of my file and Intel syntax for the rest. This feels like a kludge. Unfortunately, the information about GAS Intel mode feels a bit sparse; this page gave some hints but nothing that really helped.
Many thanks in advance. If I had reputation enough to give you a bounty, I would. :)
That seems right. You are correct that there isn't too much information on .intel_syntax. I wrote to a gal whose name I found in the source code, asking if there was any documentation. She replied that there wasn't, that she'd just reverse engineered some stuff they got from Intel. I poked around the source and found that offset flat: was required (at that time) - the colon was mandatory, too! Now, just plain offset seems to work... and there may be more documentation available, too(?).
I should think that Nasm would work with the same toolchain... no?