[Bug gdb/31436] <error reading variable: value has been optimized out> with .cfi_undefined

["lukas.graetz@tu-darmstadt.de" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=31436

--- Comment #1 from Lukas Grätz <lukas.graetz@tu-darmstadt.de> ---
(In reply to Lukas Grätz from comment #0) 
> The backtrace is still incorrect (also observed in [2]):
> 
> $ gdb bar-artificial-fix-undefined
> GNU gdb (GDB) 15.0.50.20240229-git
> 
> (gdb) run
> Starting program: bar-artificial-fix-undefined
> 
> Program received signal SIGABRT, Aborted.
> 0x00007ffff7dee00b in raise () from /lib/x86_64-linux-gnu/libc.so.6
> (gdb) bt
> #0  0x00007ffff7dee00b in raise () from /lib/x86_64-linux-gnu/libc.so.6
> #1  0x00007ffff7dcd859 in abort () from /lib/x86_64-linux-gnu/libc.so.6
> #2  0x00000000004011b0 in bar () at bar-artificial.c:30
> #3  0x00000000004011d1 in baz (
>     a=<error reading variable: value has been optimised out>, 
>     b=<optimised out>, c=<optimised out>, d=<optimised out>, 
>     e=<optimised out>, f=<optimised out>, g=48, h=49) at bar-artificial.c:38
> 
> 
> Here, the backtrace did not reach the functions qux() and main(). In this
> case, the stack base pointer rbp was clobbered and marked with
> .cfi_undefined. But it still should be possible without rbp to reconstruct
> the backtrace.


Edit: The last sentence was partly incorrect, I re-checked the assembler code.
In qux(), there is a:

        movq    %rsp, %rbp
        .cfi_def_cfa_register 6

And then rsp is clobbered in qux(). And rbp is clobbert in bar(). So the return
address from qux() is lost and main() cannot be reached by the backtrace. But
the backtrace should still have reached qux(). And the parameters a,b,c of
baz() are also reconstructable.

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