I'm wanting to set a breakpoint on a function parameter if it is greater than a certain value. Dummy code below:
uint64_t num = 123456;
uint64_t x = 847534;
uint64_t other = (num*x) - (x/num);
.... other stuff here (multithreaded stuff)
void calc(uint64_t size)
...do some stuff with size
I've tried to set a breakpoint by:
(gdb) b calc if size == 852479
but it does not know what size is since it is a parameter I'm guessing. How would I break if the parameter equals a certain number. It is NOT an option to break on all the calls to this function because it gets called a billion times in the multithreaded environment.
Assuming x86-64 calling conventions on GNU/Linux platform you could examine
%rdi (64-bit) register directly to check function's first parameter:
b calc if $rdi == 852479
This allows you to break on function
calc even if you don't have debugging symbols loaded (thus no code listing, i.e. by
Note that this method would fail if function is inlined by optimizing compiler.
break "file.c":100 if (size=852479)
break "file.c":100 if (size>852479)
here i am assuming you want the conditional breakpoint on line 100 and your src file is
i.e if you want to break on the line that calls
calc, then that would be line 100 - modify as appropriate (you would also have to substitute
other in this instance)
if you used a line no. that was one of the 1st statements in the
calc function then you would stick with
break foo if arg1 == 14 doesn't work for some reason (I've encountered some functions/binaries where it does, and where it doesn't), you can try to substitute it with
commands allows you to set some gdb commands that will be run each time breakpoint is hit. To achieve desired effect - a conditional breakpoint - you can do the following:
(gdb) b foo Breakpoint 1 at 0x400633: file test.c, line 6. (gdb) commands 1 Type commands for breakpoint(s) 1, one per line. End with a line saying just "end". >silent >if arg1 != 14 >cont >end >end
The execution will stop at breakpoint only if
arg1 == 14.
The only drawback is that
silent suppresses typical "breakpoint hit" message. You can remove
silent, but then gdb will print the message even if breakpoint is skipped by
commands script, which is undesireable if breakpoint is hit very often.
You can add some custom notification inside
command script, though.