https://gcc.gnu.org/bugzilla/show_bug.cgi?id=38534
--- Comment #29 from Lukas Grätz <lukas.gra...@tu-darmstadt.de> --- (In reply to Jakub Jelinek from comment #28) > (In reply to Lukas Grätz from comment #9) > > Well it is not my testcase. But I added backtracing and observed that the > > printed backtrace is unchanged with your patch. The new > > no_return_to_caller(): > > You haven't tried hard enough. That might be true. > Consider the testcase I've posted to the mailing list, built with -Og -g. > The gcc trunk hits the backtrace not possible problem because rbp is > > clobbered and needed in upper frame CFA computation: Yes, when a backtrace is based on rbp, one needs -fno-omit-frame-pointer. I trusted comment #10 here, as it made sense. > And in the patched gcc (with PR114116 patch to save bp register) backtrace > works but several of the values are bogus: > #2 0x00000000004011d2 in baz (a=a@entry=42, b=b@entry=43, c=c@entry=44, > d=d@entry=-559038737, e=e@entry=-559038737, f=f@entry=-559038737, g=48, > h=49) at /tmp/1.c:38 glibc's backtrace() function and friends only reports function names and addresses. This looks like the gdb bt command. I admit, I did not take a proper look into that before. I belief this could and should be somehow be fixed by adding DWARF info that certain callee-saved registers (= the function parameter values) were overwritten. The corrected backtrace could look something like this: #2 0x00000000004011d2 in baz (a=42, b=43, c=44, d=<optimised out>, e=<optimised out>, f=<optimised out>, g=48, h=49) at /tmp/1.c:38 Some parameters would be <optimised out>, and this would be fine because the code was partially compiled with -O2. It is not unusual to have <optimised out> parameter values in gdb's bt. > So, I think we should limit this to -fno-unwind-tables or maybe > -mcmodel=kernel. Now I am confused. The optimization is limited to -fexceptions. And the documentation of -funwind-tables says "Similar to -fexceptions, except". So shouldn't -funwind-tables behave similar to -fexceptions? I don't see anything kernel-specific here.
