Reading code is a very important skill for software developers. Knowing the calling sequence of a function is essential for understanding. GDB rbreak command is a powerful tool for code analysis.
rbreak
- Add break point on function names start with ngx_http
- print function using bt 1
Example of the GDB commands
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rbreak ^ngx_http
commands
silent
bt 1
continue
end
continue
I know the continue command, but I never notice the argument of the continue command.
Here is the reference of the continue command: https://sourceware.org/gdb/current/onlinedocs/gdb.html/Continuing-and-Stepping.html
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Continuing means resuming program execution until your program completes normally. In contrast, stepping means executing just one more “step” of your program, where “step” may mean either one line of source code, or one machine instruction (depending on what particular command you use). Either when continuing or when stepping, your program may stop even sooner, due to a breakpoint or a signal. (If it stops due to a signal, you may want to use handle, or use ‘signal 0’ to resume execution (see Signals), or you may step into the signal’s handler (see stepping and signal handlers).)
continue [ignore-count]
c [ignore-count]
fg [ignore-count]
Resume program execution, at the address where your program last stopped; any breakpoints set at that address are bypassed. The optional argument ignore-count allows you to specify a further number of times to ignore a breakpoint at this location; its effect is like that of ignore (see Break Conditions).
The argument ignore-count is meaningful only when your program stopped due to a breakpoint. At other times, the argument to continue is ignored.
The synonyms c and fg (for foreground, as the debugged program is deemed to be the foreground program) are provided purely for convenience, and have exactly the same behavior as continue.
To resume execution at a different place, you can use return (see Returning from a Function) to go back to the calling function; or jump (see Continuing at a Different Address) to go to an arbitrary location in your program.
Recently, I have debugged a bug using the continue heavily.
I wanted to know when a node was deleted from the link at the exact instruction. I added a breakpoint and checked the state of the list when the breakpoint was hit. Because checking the state of the list is very slow which may take 30 seconds or more. I don’t want to check on every breakpoint stop. And it is impossible to do it in this way because there are millions of the breakpoint hit. So I would like to use the binary search method.
I an wondering how to skip the breakpoint for the specified times. Thanks for the AI, I got the answer quickly.
continue ingore-count is what I want.
Because I use rr to record the execution of the program. So I can reverse the execution of the program.
And there is a reverse-continue ingore-count also.
In order to find the exact instruction, I also use the stepi N and reverse-stepi N instruction.
Thanks God! the repeat/ignore count argument make the life easier.
