Re: [GSoC][Static Analyzer] Some questions and request for a small patch to work on

[David Malcolm <dmalcolm@redhat.com>]

On Wed, 2023-03-01 at 12:16 +0100, Shengyu Huang wrote:
> Hi Dave,
> 
> > On 1 Mar 2023, at 00:59, David Malcolm <dmalcolm@redhat.com> wrote:
> > 
> > Did you get it to output your messages?
> > 
> 
> 
> Yes, I chose to emit the warning before the supergraph or exploded
> graph is created (I guess this is enough, right?). I checked out from
> the trunk a week ago, and I checked out from the latest trunk just
> now and built from modified source again, by adding a line in the
> following code in analyzer/engine.cc:
> 
> FOR_EACH_FUNCTION_WITH_GIMPLE_BODY (node) {
>   node->get_untransformed_body ();
>   warning_at (DECL_SOURCE_LOCATION (node->decl), 0, "hello world, I’m
> compiling %qE", node->decl); // ADDED
> }
> 
> Compiling my own test script without optimizations, I got the output
> (surprisingly no warning from -Wanalyzer-shift-count-negative
> anymore):
> 
> test.c: In function 'main':
> test.c:42:9: warning: left shift count is negative [-Wshift-count-
> negative]
>    42 |   b = b << -1;
>       |         ^~
> test.c: At top level:
> test.c:36:5: warning: hello world, I'm compiling 'main'
>    36 | int main()
>       |     ^~~~
> test.c:27:6: warning: hello world, I'm compiling 're'
>    27 | void re (int c)
>       |      ^~
> test.c:12:6: warning: hello world, I'm compiling 'f'
>    12 | void f (unsigned long *p, int r, int i)
>       |      ^
> test.c:9:5: warning: hello world, I'm compiling 'fun2'
>     9 | int fun2()
>       |     ^~~~
> test.c:4:5: warning: hello world, I'm compiling 'fun1'
>     4 | int fun1()
>       |     ^~~~

Looks great.

[...snip...]

> 
> 
> 
> > 
> > The next thing to do might be to try stepping through the code in
> > the
> > debugger; that's often a good way to learn about a new codebase. 
> > See:
> >  https://gcc-newbies-guide.readthedocs.io/en/latest/debugging.html
> > and maybe have a look at the support scripts mentioned on that
> > page.
> > 
> 
> I did try to use gdb more to inspect the internals, but one thing I
> noticed when using it is that I got `??()` in the backtrace, which
> I’ve never seen before. Some online sources say it happened due to
> “corrupted stack”, but I don’t know how that can happen
> either…However, after pulling changes from the trunk and rebuilding
> from the source, “??()” disappeared and now I can step through the
> execution without any problem (previously `step` and `continue` did
> not work as expected…). Do you have any clues what happened so that I
> can fix it myself later if that happens again?

I've noticed that if I invoke "make" in the top-level build directory,
when it recurses into the "gcc" subdirectory it builds with -O2,
whereas if I invoke "make" directly in the build tree's gcc
subdirectory it builds without optimization, and I get a much better
debugging experience.  Maybe that's what happened?  Because of this, I
sometimes find I have to do "rm analyzer/*.o" in the "gcc" subdirectory
of the build, and rerun "make" in there.  Though even with -O2 my gdb
still gives me function names in the backtrace, albeit on x86_64, and
probably a different version of gdb...

> 
> Best,
> Shengyu
> 
> > BTW, are you building trunk, or GCC 12?  I've made a *lot* of
> > changes
> > to the analyzer in trunk, so it would be good for you to be working
> > with something that's reasonably up-to-date.

Sounds like you're pulling from trunk; good.

Thanks
Dave