Next: Frame Info, Previous: Backtrace, Up: Stack   [Contents][Index]


8.3 Selecting a Frame

Most commands for examining the stack and other data in your program work on whichever stack frame is selected at the moment. Here are the commands for selecting a stack frame; all of them finish by printing a brief description of the stack frame just selected.

frame [ frame-selection-spec ]

f [ frame-selection-spec ]

The frame command allows different stack frames to be selected. The frame-selection-spec can be any of the following:

num

level num

Select frame level num. Recall that frame zero is the innermost (currently executing) frame, frame one is the frame that called the innermost one, and so on. The highest level frame is usually the one for main.

As this is the most common method of navigating the frame stack, the string level can be omitted. For example, the following two commands are equivalent:

(gdb) frame 3
(gdb) frame level 3

address stack-address

Select the frame with stack address stack-address. The stack-address for a frame can be seen in the output of info frame, for example:

(gdb) info frame
Stack level 1, frame at 0x7fffffffda30:
 rip = 0x40066d in b (amd64-entry-value.cc:59); saved rip 0x4004c5
 tail call frame, caller of frame at 0x7fffffffda30
 source language c++.
 Arglist at unknown address.
 Locals at unknown address, Previous frame's sp is 0x7fffffffda30

The stack-address for this frame is 0x7fffffffda30 as indicated by the line:

Stack level 1, frame at 0x7fffffffda30:

function function-name

Select the stack frame for function function-name. If there are multiple stack frames for function function-name then the inner most stack frame is selected.

view stack-address [ pc-addr ]

View a frame that is not part of GDB’s backtrace. The frame viewed has stack address stack-addr, and optionally, a program counter address of pc-addr.

This is useful mainly if the chaining of stack frames has been damaged by a bug, making it impossible for GDB to assign numbers properly to all frames. In addition, this can be useful when your program has multiple stacks and switches between them.

When viewing a frame outside the current backtrace using frame view then you can always return to the original stack using one of the previous stack frame selection instructions, for example frame level 0.

up n

Move n frames up the stack; n defaults to 1. For positive numbers n, this advances toward the outermost frame, to higher frame numbers, to frames that have existed longer.

down n

Move n frames down the stack; n defaults to 1. For positive numbers n, this advances toward the innermost frame, to lower frame numbers, to frames that were created more recently. You may abbreviate down as do.

All of these commands end by printing two lines of output describing the frame. The first line shows the frame number, the function name, the arguments, and the source file and line number of execution in that frame. The second line shows the text of that source line.

For example:

(gdb) up
#1  0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
    at env.c:10
10              read_input_file (argv[i]);

After such a printout, the list command with no arguments prints ten lines centered on the point of execution in the frame. You can also edit the program at the point of execution with your favorite editing program by typing edit. See Printing Source Lines, for details.

select-frame [ frame-selection-spec ]

The select-frame command is a variant of frame that does not display the new frame after selecting it. This command is intended primarily for use in GDB command scripts, where the output might be unnecessary and distracting. The frame-selection-spec is as for the frame command described in Selecting a Frame.

up-silently n

down-silently n

These two commands are variants of up and down, respectively; they differ in that they do their work silently, without causing display of the new frame. They are intended primarily for use in GDB command scripts, where the output might be unnecessary and distracting.

Next: Frame Info, Previous: Backtrace, Up: Stack   [Contents][Index]