Jakub Jelinek <ja...@redhat.com> writes: > On Thu, Jan 12, 2023 at 01:28:59PM +0100, Jakub Jelinek wrote: >> > Although we don't AFAIK support using DW_CFA_undefined with RA signing, >> > the failure mode would be non-obvious: it would effectively toggle the >> > bit on. >> >> We don't install unwind-dw2.h nor give user code access to the how array >> (and it just lives on the stack of __frame_state_for/uw_init_context_1 >> functions and address of it is passed to functions called from it), >> so I hope all this is private to the libgcc unwinder. After all, otherwise >> e.g. the change how "how" is represented couldn't be done. >> That said, if new enum entries are added in the generic code, then >> I think uw_update_context_1 will warn about unhandled case in a switch, >> unless we e.g. change >> case REG_UNSAVED: >> case REG_UNDEFINED: >> break; >> to >> default: >> break; >> (and provided that the new enums would want such handling).
If we have a new enum, I think we should handle it explicitly. The fact that the information isn't propagated between frames is a key part of the semantics. >> Another option is to just define the arch dependent value for how field >> in the arch code, right now it is unsigned char type, so using say >> (unsigned char) ~0 or (unsigned char) ~0 and (unsigned char) ~1 as arch >> specific values might be ok too. > > Yet another option would be to define 1-2 extra REG_ values in the generic > unwind-dw2.h header, but name them > REG_ARCH_SPECIFIC_1, > REG_ARCH_SPECIFIC_2, > or so, and then the machine specific code can > #define REG_AARCH64_TOGGLE_ON REG_ARCH_SPECIFIC_1 > Of course, all this depends on whether the arch specific codes can be > handled in uw_update_context_1 by doing break; there and nothing else. Yeah, personally I'd prefer for target-independent code to provide the toggle representation, even if it isn't widely used. Thanks, Richard
