On Mon, Apr 09, 2018 at 11:50:14PM -0600, Jan Beulich wrote:
> >> As ICC generates the same assembly on the instructions:
> >> mov eax, DWORD PTR k1[rip]
> >> ...
> >> mov eax, DWORD PTR xmm0[rip]
> >> I think either the intel syntax spec is faulty, or gas is buggy and should
> >> figure out that after *WORD PTR and before [ there is symbol rather than
> >> register name. Some testcases e.g. have k1 as function name and that
> >> results in other asm errors (about .size directive).
> >
> >How does Intel syntax support symbols like eax, k1 and xmm0 with
> >".intel_syntax noprefix"?
>
> I've noticed this problem about two weeks ago as well, and have a patch
> mostly ready (but need to get around to both produce a proper testcase
> and regression test the whole thing); that won't be until in a couple of
> weeks time, though - if you think this is needed earlier, I can hand you
> the fragments I have. As an aside - you realize this isn't an Intel syntax
> only issue, as "noprefix" can as well be specified with .att_syntax.
>
> I should note though that the fix won't go as far a Jakub suggests: Context
> doesn't matter for recognizing whether a symbol is a register. For something
> like the above to compile, .arch would need to be used to disable the
> respective register groups (e.g. .arch .noavx512f to make k1 an ordinary
> symbol).
That means there are still lots of valid programs that will never compile
with the noprefix syntax, because you really can't disable those register
groups when you need them. Consider
int eax;
int foo (void) { return eax; }
int ebx (void) { return 23; }
/tmp/ccJBZxhZ.s: Assembler messages:
/tmp/ccJBZxhZ.s:15: Error: invalid use of register
/tmp/ccJBZxhZ.s: Error: .size expression for ebx does not evaluate to a constant
Line 15 is:
mov eax, DWORD PTR eax[rip]
and the .size expression is:
.size ebx, .-ebx
And no, this isn't artificial, it appears e.g. quite a lot in GCC testsuite.
So, what should the compiler do if it detects such identifiers in an
instruction? Temporarily do .intel_syntax prefix and prefix all the
registers, then revert?
Jakub
