https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119388
Bug ID: 119388
Summary: [12/13/14/15 Regression] -isystem does not disable
warnings coming from system headers
Product: gcc
Version: 15.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: dangelog at gmail dot com
Target Milestone: ---
When upgrading from GCC 11 to 13/14, some warnings start to appear from headers
that have been included via -isystem.
A minimal example would be creating a header containing this:
#include <iostream>
class Stuff {
int x;
public:
Stuff() { std::cout << x; }
};
And then including it via -isystem, and creating a Stuff object somewhere.
Under -O2 -Wall -Wextra this yields on GCC 14:
/app/my_includes/stuff.h:9:28: warning: 's.Stuff::x' is used uninitialized
[-Wuninitialized]
9 | Stuff() { std::cout << x; }
Whereas nothing was emitted on GCC 11.
I've assembled a somehow more flexible example here on Godbolt:
https://gcc.godbolt.org/z/c1Ts3ze87
You can play with:
- different GCC versions / compiler option (anything above 11 will trigger the
warning; 11 will as well, if disabling system headers)
- the `#pragma GCC system_header`
- setting SYSTEM in the CMakeLists.txt (so that CMake uses -isystem)
- disabling inlining of f() into main() (which will suppress a second warning)
In projects using Qt we're randomly seeing this for optimization-related
warnings: -Wnull-dereference, -Wstrict-overflow, -Wmaybe-uninitialized. Some
degree of optimization seems to be necessary.
Apologies, it's highly probable that there could be duplicates of this, but
bugzilla's search isn't really the best.
