How to execute commands conditionally in gdbinit functions

Question

I have a gdb function, defined in gdbinit file:

define myfunc 
    set $retval = SOMEHOW_RET_VALUE_OF shell my-shell-command
    if $retval == 0
       load my-output
    else
       echo command not succeeded, not doing anything.\n
    end 
end

How can I get my-shell-func return status and use it to control loading new binary output?

is this useful?? https://stackoverflow.com/questions/12572631/return-a-value-via-a-gdb-user-defined-command — Pavan Chandaka, Dec 16 '17 at 19:35
I'm afraid it isn't. The key point is getting the `shell my-shell-command` output to a variable. — ceremcem, Dec 16 '17 at 22:17

score 2 · Accepted Answer · answered Dec 19 '17 at 16:29

There are two ways to do this.

The simplest way is to use gdb's built-in Python scripting capability. For a case like the above, you could write a new convenience function that does what you like. A convenience function is appropriate here because it can be used directly in an expression.

To write a convenience function, look through the docs for gdb.Function.

Then you would use it like:

set $retval = $_shellcommand("shell command")

If you'd rather not dive into Python, there is still a way; although it is somewhat more painful.

For a simple shell command, the idea would be to write the exit status of the shell command to a gdb script file, which you then source:

(gdb) shell false; echo "set \$retval = $?" > /tmp/q
(gdb) source /tmp/q
(gdb) print $retval
$1 = 1

This gets somewhat hairier if you want more than just the exit status, or if you want to use output from gdb commands in the computation.

Second "simple approach" worked quite well. Thank you. – ceremcem Dec 20 '17 at 09:12 — ceremcem, Dec 20 '17 at 09:12

How to execute commands conditionally in gdbinit functions

1 Answers1