https://gcc.gnu.org/bugzilla/show_bug.cgi?id=38534
--- Comment #10 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to Lukas Grätz from comment #9)
> Well it is not my testcase. But I added backtracing and observed that the
> printed backtrace is unchanged with your patch. The new
> no_return_to_caller():
>
> void __attribute__((noreturn))
> no_return_to_caller(int a, int b, int c, int d)
> {
> LOOP_BODY;
>
> #define BT_BUF_SIZE 100
> void *buffer[BT_BUF_SIZE];
> backtrace_symbols_fd(buffer, backtrace(buffer, BT_BUF_SIZE),
> STDOUT_FILENO);
>
> while (1);
> }
>
> What I observed from the assembly is that %rbp is not saved, whereas %rip
> and %rsp are still implicitly saved by the call instruction. But since
> glibc's backtrace implementation does not use %rbp, this is fine.
>
> Some amateur speculation, just ignore it: I don't know whether %rbp is the
> source of the failed C++ test cases, which also do some stack unwinding.
> After looking in the System V Abi specification I am still unsure whether
> stack unwinding relies on %rbp or not. Perhaps there is an unnecessary
> dependency on %rbp or a missing "-fno-omit-frame-pointer" somewhere in the
> gcc internals that causes the problem.
The C++ test issue is caused by missing callee-saved registers for
exception supports in noreturn functions in libstdc++. I fixed it by
keeping callee-saved registers when exception is enabled.
Backtrace with %rbp is unrelated to this. Gcc will skip %rpb without
-fno-omit-frame-pointer.
