On Wed, Feb 28, 2024 at 10:20 PM Hongtao Liu <crazy...@gmail.com> wrote: > > On Wed, Feb 28, 2024 at 4:54 PM Jakub Jelinek <ja...@redhat.com> wrote: > > > > Hi! > > > > Adding Hongtao and Honza into the loop as the ones who acked the original > > patch. > > > > The no_callee_saved_registers by default for noreturn functions change can > > break in-process backtrace(3) or backtraces from debugger or other process > > (quite often, any time the noreturn function decides to use the bp register > > and any of the parent frames uses a frame pointer; the unwinder just crashes > > in the libgcc unwinder case, gdb prints stack corrupted message), so I'd > > like to save bp register in that case: > > > > https://gcc.gnu.org/pipermail/gcc-patches/2024-February/646591.html > I think this patch makes sense and LGTM, we save and restore frame > pointer for noreturn. > > > > and additionally the no_callee_saved_registers by default for noreturn > > functions change can make debugging harder, again not localized to the > > noreturn function, but any of its callers. So, if say glibc abort function > > implementation needs a lot of normally callee-saved registers, no matter how > > users recompile their apps, they will see garbage or optimized out > > vars/parameters in their code unless they rebuild their glibc with -O0. > > So, I think we should guard that by a non-default option: > > > > https://gcc.gnu.org/pipermail/gcc-patches/2024-February/646649.html > So it turns off the optimization for noreturn functions by default, > I'm not sure about this. > Any comments, H.J?
We need BP for backtrace. I don't think we need to save other registers. True, GDB may not see function parameters. But optimization always has this impact. When I need to debug a program, I always use -O0 or -Og. > > > > Plus we need to somehow make sure to emit DW_CFA_undefined for the modified > > but not saved normally callee-saved registers, so that we at least don't get > > garbage in debug info. H.J. posted some patches for that, so far I wasn't > > happy about the implementation but the actual change is desirable. > > > > Your thoughts on this? > > > > Jakub > > > > > -- > BR, > Hongtao -- H.J.
