Sorry for the slow response, was out for a few days. Xi Ruoyao <xry...@mengyan1223.wang> writes: > On Sat, 2022-03-12 at 18:48 +0800, Xi Ruoyao via Gcc-patches wrote: >> On Fri, 2022-03-11 at 21:26 +0000, Qing Zhao wrote: >> > Hi, Ruoyao, >> > >> > (I might not be able to reply to this thread till next Wed due to a >> > short vacation). >> > >> > First, some comments on opening bugs against Gcc: >> > >> > I took a look at the bug reports PR104817 and PR104820: >> > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104820 >> > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104817 >> > >> > I didn’t see a testing case and a script to repeat the error, so I >> > cannot repeat the error at my side. >> >> I've put the test case, but maybe you didn't see it because it is too >> simple: >> >> echo 'int t() {}' | /home/xry111/git-repos/gcc-test-mips/gcc/cc1 - >> nostdinc -fzero-call-used-regs=all >> >> An empty function is enough to break -fzero-call-used-regs=all. And >> if >> you append -mips64r2 to the cc1 command line you'll get 104820. I >> enabled 4 existing tests for MIPS (reported "not work" on MIPS) in the >> patch so I think it's unnecessary to add new test cases. >> >> Richard: can we use MIPS_EPILOGUE_TEMP as a scratch register in the >> sequence for zeroing the call-used registers, and then zero itself >> (despite it's not in need_zeroed_hardregs)? > > No, it leads to an ICE at stage 3 bootstrapping :(. > > Now I think the only rational ways are: > > (1) allow zeroing more registers than need_zeroed_hardregs.
I think this is the way to go. I agree it's a bit hacky, but it seems like the least worst option. A less hacky alternative would be to pass an extra argument to the hook that contains the set of registers that the hook is *allowed* to clobber. For -fzero-call-used-regs=X, this new argument would be the set that would have been chosen for -fzero-call-used-regs=all, regardless of what X actually is. We could then assert that the extra registers we want to clobber are in that set (which will be true for all values of X). > Or > > (2) allow zeroing less registers than need_zeroed_hardregs (then I'll > skip ST_REGS, after all they are just 8 bits in total). Yeah, this is explicitly OK, provided that the target maintainers feel that the contents of the registers in question are not a significant security concern. I don't feel I can make that call though. It's really a question for the userbase. Thanks, Richard > If all these are unacceptable, then > > (3) I'll just call sorry in MIPS target hook to tell not to use this > feature on MIPS.
