https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97321
Bug ID: 97321
Summary: add warning for pointer casts that may lead to
aliasing violation when dereferenced
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: nsz at gcc dot gnu.org
Target Milestone: ---
consider:
int f(unsigned char **);
int g(char *p)
{
return f((unsigned char **)&p);
}
such code is almost surely wrong (if f dereferences its
argument) this is a common mistake and it seems gcc-11
will optimize such code more aggressively which can lead
to broken behavior, see bug 97264.
so it would be useful to simply warn about casts between
pointer types that cannot alias. e.g.:
"warning: dangerous cast from `char **` to `unsigned char **` can lead to
aliasing violation [-Wpointer-cast]"
does not have to be in -Wall, but the current aliasing
warnings are too weak to catch bugs like in the example.
