On Fri, Nov 19, 2021 at 10:39:15AM +0100, Christian Borntraeger wrote: > > So if I understand > > https://sourceware.org/binutils/docs/as/s390-Directives.html#s390-Directives > > https://sourceware.org/binutils/docs/as/s390-Formats.html > > that `e,` prefix is for 16B opcodes? > > e is an instruction format as specified by the architecture. > See http://publibfp.dhe.ibm.com/epubs/pdf/a227832c.pdf > without any parameters. > Normally RR would be the right thing for MVCL, but since > we try to build an invalid opcode without the assembler > noticing (ab)using e seem like a safer approach. > > > > LGTM, thanks again. > > Suggested-by: Ulrich Weigand <Ulrich.Weigand@xxxxxxxxxx> > > Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > > added those and added my RB. applied to the s390 tree. Thanks .. > > > diff --git a/arch/s390/lib/test_unwind.c b/arch/s390/lib/test_unwind.c > > > index cfc5f5557c06..d342bc884b94 100644 > > > --- a/arch/s390/lib/test_unwind.c > > > +++ b/arch/s390/lib/test_unwind.c > > > @@ -176,7 +176,7 @@ static noinline int unwindme_func4(struct unwindme *u) > > > * trigger specification exception > > > */ > > > asm volatile( > > > - " mvcl %%r1,%%r1\n" > > > + " .insn e,0x0e11\n" /* mvcl %%r1,%%r1" */ Sorry, I disagree with this. As you said above rr would be the correct format for this instruction. If we go for the e format then we should also use an instruction with e format. Which in this case would simply be an illegal opcode, which would be sufficient for what this code is good for: ".insn e,0x0000". Plus a fixup of the comment above, since this would generate an operation insteand of a specification exception. Just a generic "exception" would be good enough for the comment.
