Hi Dave,
> On 1 Mar 2023, at 00:59, David Malcolm <[email protected]> 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()
| ^~~~
test.c: In function 'main':
test.c:40:8: warning: use of uninitialized value 'a' [CWE-457]
[-Wanalyzer-use-of-uninitialized-value]
40 | int* c = a;
| ^
'main': events 1-3
|
| 38 | int* a;
| | ^
| | |
| | (1) region created on stack here
| | (2) capacity: 8 bytes
| 39 | int b = 'c';
| 40 | int* c = a;
| | ~
| | |
| | (3) use of uninitialized value 'a' here
|
~~
If I compiled it with -O2, I got additionally
test.c: In function 'f':
test.c:20:34: warning: shift by count ('64') >= precision of type ('64')
[-Wanalyzer-shift-count-overflow]
20 | p[i--] = b + 1 >= 64 ? 0UL : 1UL << (b + 1);
| ~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~
'f': events 1-5
|
| 16 | while (i >= 0)
| | ~~^~~~
| | |
| | (1) following 'true' branch (when 'i >= 0')...
| 17 | {
| 18 | if (n > b)
| | ~
| | |
| | (2) ...to here
| | (3) following 'true' branch (when 'b < n')...
| 19 | {
| 20 | p[i--] = b + 1 >= 64 ? 0UL : 1UL << (b + 1);
| | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| | | |
| | | (4) ...to here
| | (5) shift by count '64' here
|
which is documented as a false positive in PR98447.
>
> 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?
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.
