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.
- Select frame number n. 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-numbered frame is the one for
- Select the frame at address 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.
On the SPARC architecture,
frameneeds two addresses to select an arbitrary frame: a frame pointer and a stack pointer.
On the MIPS and Alpha architecture, it needs two addresses: a stack pointer and a program counter.
On the 29k architecture, it needs three addresses: a register stack pointer, a program counter, and a memory stack pointer.
- Move n frames up the stack. For positive numbers n, this advances toward the outermost frame, to higher frame numbers, to frames that have existed longer. n defaults to one.
- Move n frames down the stack. For positive numbers n, this
advances toward the innermost frame, to lower frame numbers, to frames
that were created more recently. n defaults to one. You may
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.
(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
See Printing Source Lines,
- These two commands are variants of
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.