GDB as a program analyzer - some thoughts

Alexandre Courbot
Tue May 18 14:57:00 GMT 2004

This post deals about using GDB for non-debugging purposes, I hope it's 
not offtopic. I'm also hoping to find some people interested in the same 
matters than I to discuss about how GDB could be improved for analysis 

My few posts here have been basically about it. GDB is great to extract 
datas out of a program and output them to a file. It's very different to 
gprof - for instance, it's useful to graphically measure the efficiency 
of one memory manager against another, by placing breakpoints at memory 
allocation functions and recording the amount of memory used there. The 
recorded datas can then proove that, with some strategy, we saved a few 
garbage collections and therefore gained speed.

This is of course nothing you can't do with printfs enclosed inside 
#ifdef DEBUGs, but the advantage is that GDB allows you to do it in a 
non-intrusive and much more flexible way. I'm surprised that I haven't 
found a solutions dedicated to that - and so far, gdb is by far the best 
solution I've found. Writing a gdb script + the corresponding gnuplot 
script results in easy to get graphes of whatever you want in your program.

If people are interested in it, I can post some of the scripts I'm using 
with their result. I can also write a tutorial page on that topic.

I have some non-elegant bits in my scripts however. They mainly concern 
breakpoints. Since the breakpoints are set into gdb scripts, it's better 
if they reference symbols like function names instead of 
file:line_number pairs. The line of the breakpoint might move in future 
code modifications, and the gdb script won't be updated accordingly. 
Unfortunately, breaking at the very beginning of the function you are 
interested doesn't give you the data that has been computed inside.

So, I wonder if some breakpoint settings would be implementable with gdb 
(or if they can already be expressed and I missed them):
- Setting a breakpoint at the returning of a function
- Setting a breakpoint at some fixed point of a function (for instance, 
a C label)
- Any other breakpoint setting that is not line-number based and would 
support source modification

Would these features be desirable? Would they not?

Alexandre Courbot - PhD student

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