https://gcc.gnu.org/bugzilla/show_bug.cgi?id=38534
--- Comment #19 from Jakub Jelinek <jakub at gcc dot gnu.org> --- (In reply to H.J. Lu from comment #18) > (In reply to Jakub Jelinek from comment #17) > > E.g. shouldn't it at least be disabled for -O0 and -Og and shouldn't we > > We can disable this for -O0 and -Og. I think we should go for that. > > somehow indicate in DWARF unwind info that the callee saved registers > > weren't saved and were clobbered? Even if backtrace itself still works make > > Is there such a DWARF bit? There is the undefined state (DW_CFA_undefined, .cfi_undefined directive in gas). But DWARF says undefined is the default state unless an ABI specifies something else for certain registers (or unless overridden in CIE or FDE), so I must say I don't remember what is done usually and whether the default state isn't what is enough. But it would really surprise me if the call saved registers weren't treated as same_value at the start of the function and I believe nothing emits DW_CFA_same_value in the CIEs.
