What are the letters in gcc-inline assembly for %esp and %ebp? I understand that:
a = eax
b =ebx
c = ecx
d = edx
S = esi
D = edi
I = constant value (0 to 31).
1 Answers
6
votes
There's a list in the manual for the gcc machine constraints (see under the : Intel 386 section). The gory details (typically more up to date than the manual) are found in the i386/constraints.md file.
However - for good reasons, namely stack coherency, %ebp and %esp cannot be used as constraints. They cannot be specified as inputs or outputs in extended asm syntax. This may also extend to %ebx in some cases - specifically, when generating position-independent code, e.g., with the (i386 SysV) ELF ABI.
You can still manipulate these registers in the asm block explicitly, of course.
