Re: [patch/rfc] The off again, on again, PC == 0 in get_prev_frame

[Andrew Cagney <cagney@gnu.org>]

> Andrew, I think that this case is completely broken.  The frame chain
> isn't properly terminated.  The clone(2) system call that has created
> this thread tries to mark frame #3 as the outermost frame by clearing
> %rbp.  However, since most amd64 code doesn't use the frame pointer,
> this is pointless; GDB doesn't look at it.  The fact that you're
> seeing a zero PC here is merely accidental; it just happens to be that
> (%rsp) contains zero.  Therefore I don't think we should consider a
> zero PC as a marker for the end of the frame chain.
> 
> The Linux folks should add proper CFI to the implementation of
> close(2) in glibc.  A DW_CFA_def_cfa rule that sets the CFA to %rbp
> should do the trick.

clone(2)?  How come the trad unwind code doesn't recover?

Thinking about it, the test would stop this backtrace:

	sigsegv_handler
	<signal trampoline>
	"null"
	foo (which called "null")
	main

is this tested anywhere?

Andrew