Segher Boessenkool <seg...@kernel.crashing.org> writes: > On Tue, Jan 08, 2019 at 12:03:06PM +0000, Richard Sandiford wrote: >> Bernd Edlinger <bernd.edlin...@hotmail.de> writes: >> > Meanwhile I found out, that the stack clobber has only been ignored up to >> > gcc-5 (at least with lra targets, not really sure about reload targets). >> > From gcc-6 on, with the exception of PR arm/77904 which was a regression >> > due >> > to the underlying lra change, but fixed later, and back-ported to >> > gcc-6.3.0, >> > this works for all targets I tried so far. >> > >> > To me, it starts to look like a rather unique and useful feature, that I >> > would >> > like to keep working. >> >> Not sure what you mean by "unique". But forcing a frame is a bit of >> a slippery concept. Force it where? For the asm only, or the whole >> function? This depends on optimisation and hasn't been consistent >> across GCC versions, since it depends on the shrink-wrapping >> optimisation. (There was a similar controversy a while ago about >> to what extent -fno-omit-frame-pointer should "force a frame".) > > It's not forcing a frame currently: it's just setting frame_pointer_needed. > Whatever happens from that is the target's business.
Do you mean the asm clobber or -fno-omit-frame-pointer? If the option, then yeah, and that was exactly what was controversial :-) >> The effect on the redzone seems like something that should be specified >> explicitly rather than as an (accidental?) side effect of listing the >> sp in the clobber list. Maybe this would be another use for the "asm >> attributes" proposal. "noreturn" was another attribute suggested on >> IRC yesterday. > > Redzone is target-dependent. Right. Target-dependent asm attributes wouldn't be a problem though. Most other things about an asm are target-dependent anyway. > "noreturn"... What would that mean, *exactly*? It cannot execute any > code the compiler can see, so such asm is better off as real asm anyway > (not inline asm). "Exactly" is a strong word, and this wasn't my proposal, but... I think it would act like a noreturn call to an unknown function. Output operands wouldn't make sense, and arguably clobbers wouldn't either. Thanks, Richard >> But either way, the general feeling seems to be that going straight to a >> hard error is too harsh, since there's quite a bit of existing code that >> has the clobber. This patch implements the compromise discussed on IRC >> yesterday of making it a -Wdeprecated warning instead. > > The patch looks fine to me. Thanks! > > > Segher
