https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110899
--- Comment #9 from Michael Matz <matz at gcc dot gnu.org> --- (In reply to Florian Weimer from comment #8) > (In reply to Michael Matz from comment #7) > > > > Does the clang implementation take into account the various problematic > > > > cases that arise when calling a normal function from a (say) > > > > preserve_all > > > > function > > > > (hint: such call can't usually be done)? > > > > > > How so? We need to version the __preserve_most__ attribute with the ISA > > > level, of course. > > > > I don't see how that helps. Imagine a preserve_all function foo that calls > > printf. How do you propose that 'foo' saves all parts of the SSE registers, > > even those that aren't invented yet, or those that can't be touched by the > > current ISA? (printf might clobber all of these) > > Vector registers are out of scope for this. Why do you say that? From clang: "Furthermore it also preserves all floating-point registers (XMMs/YMMs)." (for preserve_all, but this bugreport does include that variant of the attribute). > But lets look at APX. If printf is recompiled to use APX, then it will > clobber the extended register file. If we define __preserve_most__ the way > we do in my psABI proposal (i.e., *not* as everything but %r11), the > extended APX registers are still caller-saved. Right, for preserve_most _with your wording_ it works out. preserve_all or preserve_most with clang wording doesn't. > (These details are the main reason why I want this in the psABI > documentation. This stuff is out there and will be used, so let's make sure > that it's somewhat reasonable.) I agree with that. I just want a little hashing-out-the-details before putting anything in the psABI.
