On Mon, 17 Dec 2018 at 14:35, Richard Sandiford <richard.sandif...@arm.com> wrote: > > Christophe Lyon <christophe.l...@linaro.org> writes: > > On Mon, 17 Dec 2018 at 12:47, Richard Sandiford > > <richard.sandif...@arm.com> wrote: > >> > >> Dimitar Dimitrov <dimi...@dinux.eu> writes: > >> > On Sun, Dec 16 2018 at 14:36:26 EET Bernd Edlinger wrote: > >> >> Hi, > >> >> > >> >> if I understood that right, then clobbering sp is and has always been > >> >> ignored. > >> > >> PR77904 was about the clobber not being ignored, so the behaviour > >> hasn't been consistent. > >> > >> I'm also not sure it was always ignored in recent sources. The clobber > >> does get added to the associated rtl insn, and it'd be surprising if > >> that never had an effect. > >> > >> >> If that is right, then I would much prefer a warning, that says exactly > >> >> that, because that would also help to understand why removing that > >> >> clobber > >> >> statement is safe even for old gcc versions. > >> > >> If the asm does leave sp with a different value, then it's never been safe, > >> regardless of the gcc version. That's why an error seems more appropriate. > >> > >> > Thank you. Looks like general consensus is to have a warning. See > >> > attached > >> > patch that switches the error to a warning. > >> > >> I don't think there's a good reason to treat this differently from the > >> preexisting PIC register error. If the argument for making it a warning > >> rather than an error is that the asm might happen to work by accident, > >> then the same is true for the PIC register. > >> > > > > If we leave the error, maybe a more explanatory message would be helpful? > > (along the lines of what I posted earlier in this thread, which may be > > too verbose) > > The message in that patch suggested removing the clobber and hoping for > the best, which IMO is bad advice. If the current message doesn't make > it clear enough that changing the sp is not allowed, how about: > > inline %<asm%> statements must not change the value of the stack pointer > > ? >
My understanding is that in some cases, some users still want to deliberately change SP, so "must not" may be confusing in such cases? > Thanks, > Richard > >
