Re: Specify frame by address

[Jan Kratochvil <jan.kratochvil@redhat.com>]

Hi Eli,

On Sat, 29 Oct 2011 19:12:36 +0200, Eli Zaretskii wrote:
>   An argument specifies the frame to select.
>   It can be a stack frame number or the address of the frame.  <<<<<<<<<<
>   With argument, nothing is printed if input is coming from
>   a command file or a user-defined command.
> 
> But what is "the address of the frame"?  I thought that using an
> address of a function (the one shown by "info address") or some
> address shown by the "backtrace" command would do, but none of them
> seems to work.

See the bottom of parse_frame_specification_1.

"address of the frame" is frame_id.stack_addr.  For DWARF it is CFA
(dwarf2_frame_cfa), which is for most arches just unwound SP (not PC!), that
is SP as shown by GDB in the caller.

(gdb) info frame
Stack level 5, frame at 0x7fffffffd880:
[...]
(gdb) up
#6  0x0000000000486e82 in captured_command_loop (data=0x0) at ./main.c:234
(gdb) p/x $sp
$1 = 0x7fffffffd880
(gdb) frame 0
(gdb) frame 0x7fffffffd880
#5  0x00000000006f1421 in current_interp_command_loop () at interps.c:309


> The context of this is that I would like to write a command that
> automatically goes to a frame within a call to a specific function,
> because that command needs to access variables local to that function.

Such command really needs to iterate the frames and compare PC there.


Regards,
Jan