Re: behavior of 'step' command in scripts execution

On 14-01-25 09:14 PM, dgutson . wrote:
> Why a step command stops the execution of a breakpoint's commands?
> 
> For example, consider these files:
> 
> //file.cpp:
> #include <iostream>
> using namespace std;
> 
> int f(int x)
> {
>     x++;          // this is line 6
>     return x;
> }
> 
> int main()
> {
>     cout << f(3);
> }
> 
> // file.gdb
> br file.cpp:6
> comm
> silent
> step
> set x=5
> cont
> end
> 
> When I run gdb with the binary and the script, execution stops in the
> "return x" line (line 7), getting gdb's prompt and x is not modified.
> If I enter "continue", "4" is shown.
> I observe this behavior since many versions ago (don't recall since
> when, and I don't know if it has ever been in another way). I compiled
> the example with -ggdb3 option.
> 
> What I would expect is that the breakpoint's commands execute all, and
> get "5" as output.
> 
> If there is agreement, I'd like to write a patch to fix this behavior
> through a setting, something like
>     set set-behavior continue
> or alike, so it won't break compatibility.
> 
> Thanks,
>    Daniel.

Hi Daniel,

From the GDB manual:

> You can use breakpoint commands to start your program up again. Simply use
> the continue command, or step, or any other command that resumes execution.

> Any other commands in the command list, after a command that resumes
> execution, are ignored. This is because any time you resume execution (even
> with a simple next or step), you may encounter another breakpoint—which
> could have its own command list, leading to ambiguities about which list to
> execute.

I think that sums it up pretty well. If you want to make a mode where this is allowed, you should think carefully how those ambiguities will be handled.

Simon

Source: https://sourceware.org/gdb/onlinedocs/gdb/Break-Commands.html#Break-Commands