Messages in this thread | | | Date | Tue, 3 Nov 2020 12:47:39 -0600 | From | Segher Boessenkool <> | Subject | Re: [PATCH v5 04/17] x86/acrn: Introduce hypercall interfaces |
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On Tue, Nov 03, 2020 at 05:44:35PM +0100, Borislav Petkov wrote: > On Mon, Nov 02, 2020 at 05:18:09PM -0600, Segher Boessenkool wrote: > > That is invalid actually: local register asm as input to an inline asm > > should use *that* register! > > > > This is all correct until LRA ("reload"). Not that "movl %xmm0,$eax" > > works, but at least it screams its head off, as it should. > > Screams how?
$ cat xmm1.s movl %xmm0,%eax
$ x86_64-linux-as xmm1.s -o xmm1.o xmm1.s: Assembler messages: xmm1.s:1: Error: unsupported instruction `mov'
(This isn't an existing insn IIUC.)
> It builds fine without a single peep with -Wall here. > > Btw, that's a MOVD - not a MOVL. MOVD can do xmm -> gpr moves. And > singlestepping it with gdb does, well, something, which is clearly > wrong but nothing complains: > > => 0x555555555131 <main+12>: movd %xmm0,%eax > > and %xmm0 has: > > (gdb) p $xmm0 > $2 = {v4_float = {0.99000001, 0, 0, 0}, v2_double = {5.2627153433055495e-315, 0}, v16_int8 = {-92, 112, 125, 63, > ^^^^^^^^^^ > > so that is correct.
The original code had movl. And movl is needed for GPRs.
> and that same value goes into %r8d: > > mov %eax,%r8d
Which violates what is required by register asm :-(
> > Yes. But GCC doing what you should have said instead of doing what you > > said, is not good. > > Oh well, should I open a low prio bug, would that help?
Sure, thanks!
> I probably should test with the latest gcc first, though...
Yeah... FWIW, I tested with x86_64-linux-gcc (GCC) 11.0.0 20201015 (experimental) so I doubt current ToT will have it fixed, but who knows.
Thanks,
Segher
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