The rationale from back in 2010 is in http://lists.gnu.org/archive/html/libunwind-devel/2010-04/msg00060.html plus surrounding thread, with earlier context on unwind failures in http://lists.gnu.org/archive/html/libunwind-devel/2010-03/msg00015.html
There's also related earlier context in http://lists.gnu.org/archive/html/libunwind-devel/2008-01/msg00017.html As I mentioned in the first linked message, it seems improbable that unw_init_local() could ever be invoked from a signal frame itself. At that time, your use case of single stepping was mentioned as a counter-example. Would unw_init_remote() work for your use? On Fri, Mar 24, 2017 at 11:23 PM, Doug Moore <do...@rice.edu> wrote: > Your change of Apr 24 2010 introduced the second argument to common_init, > and used it to pass 1 (use_prev_instr set) from unw_init_local and 0 > (use_prev_instr clear) from unw_init_remote. I don’t know how those > choices were made, but for my purposes, the choice for unw_init_local was > wrong, and I have to change that decision in the copy of libunwind that > we’ll use here. I’d welcome an explanation of that decision. > > Doug > > > On Mar 24, 2017, at 11:37 AM, Lassi Tuura <l...@iki.fi> wrote: > > What platform are you on? fetch_proc_info() should auto-detect signal > frame and set use_prev_instr accordingly using the (kernel-provided) frame > annotations detected in parse_cie(). I don't know if that works for > anything but linux (and possibly x86_64 only at that). Looks like there may > be some support for freebsd. > > On Thu, Mar 23, 2017 at 8:45 PM, Doug Moore <do...@rice.edu> wrote: > >> When unw_init_local uses common_init to set use_prev_instr, and then >> fetch_proc_info decrements ip, based on use_prev_instr, unw_step fails for >> me. >> >> I’m putting a temp break point at the start of _dl_runtime_resolve, and >> when gdb gets there, I’m sending a signal to trigger a signal handler that >> invokes unw_step. What happens, sadly, is that the instruction pointer is >> decremented, so the eh_frames search doesn’t find the right frame, so the >> step fails. >> >> If only I could clear that use_prev_instr field. So far, I don’t have >> any better choices than to hack the libunwind source and maintain my own >> local branch. Are there any better ideas? >> >> Doug >> _______________________________________________ >> Libunwind-devel mailing list >> Libunwind-devel@nongnu.org >> https://lists.nongnu.org/mailman/listinfo/libunwind-devel >> > > !DSPAM:10223,58d54b7039342953010367! > > >
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