On Feb 24 15:28, Jon TURNEY wrote: > On 23/02/2015 21:24, Corinna Vinschen wrote: > >On Feb 23 18:15, Jon TURNEY wrote: > >>I really wanted to do this by adding some DWARF CFI to the generated sigfe.s > >>file, but there doesn't seem to currently be a way to correctly describe > >>_sigbe's frame using that. > > > >I was wondering about this already. It seems weird if the CFI stuff > >doesn't allow for a situation like that > > My understanding is limited, but it seems to me that it only describes > register unwinding, not unwinding the state of an arbitrary memory location. > > After writing my patch, which only unwinds one sigstack entry correctly, I > went back and had another go at writing the equivalent CFI, which I think > should be possible, but I still couldn't get it to work. > > I'll take another look.
Maybe the binutils folks can help? > >>So instead, write a custom unwinder for _sigbe frames, which gets the return > >>address from the sigstack. > >> > >>Implemented for i386 and amd64. > > > >Cool. Really. But, shouldn't that go to the gdb-patches mailing list? > > > >>4. This unfortunately ends up hardcoding into gdb the offset of sigstackptr > >>in > >>the cygwin TLS area from the top of stack, and so will break if that > >>changes. > >>Hopefully that doesn't happen to often. > > > >It happens too often to be ignored. Wouldn't it make sense to add > >a cygwin_internal call to return tls offsets or addresses, the later > >if the argument is a pointer to the stack or cygtls area? > > That's not going to give the right answer when remote debugging. Uh, good point. > But the offset is, of course, encoded into the _sigbe routine, so the better > approach is probably to extract it from there. You mean scanning the code and extracting the offset right from the opcodes? That's an... interesting... idea. I would probably object to it, but can't be bothered, considering Cygwin is doing the same with ntdll.dll ;) Corinna -- Corinna Vinschen Please, send mails regarding Cygwin to Cygwin Maintainer cygwin AT cygwin DOT com Red Hat
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