Ævar Arnfjörð Bjarmason <avarab@xxxxxxxxx> writes: > The pre-release GCC 12.0 development branch has a new warning about > dangling pointers in -Wall: > > http.c: In function ‘run_active_slot’: > http.c:1332:24: error: storing the address of local variable ‘finished’ in ‘*slot.finished’ [-Werror=dangling-pointer=] > 1332 | slot->finished = &finished; > | ~~~~~~~~~~~~~~~^~~~~~~~~~~ > http.c:1330:13: note: ‘finished’ declared here > 1330 | int finished = 0; > | ^~~~~~~~ > > This is on a locally built "gcc (GCC) 12.0.1 20220120 (experimental)", > built from gcc.git's 8bc700f4c3f (Enhance vec_pack_trunc for integral > mode mask., 2022-01-17). > > The GCC warning is specifically about pointers that survive the exit > of the function. See a comment added to > "pass_waccess::use_after_inval_p" in the GCC commit that added the > warning, or: > > /* The use is one of a dangling pointer if a clobber of the variable > [the pointer points to] has not been found before the function exit > point. */ > [...] > > There's a few possible ways to fix this, but the simplest is to assign > NULL to "slot->finished" at the end of run_active_slot(), it's the > only caller that ever assigns non-NULL to it. It was suggested[2] to > guard that with "if (slot->finished == &finished)", but that'll still > trigger the warning. Does that mean we can clobber the finished member of a slot that was in use, not the one we prepared, because we do not make sure we do not clobber slot->finished that other people set up? I think this change is safe, but it's been quite a while since I played with dumb HTTP walker the last time, so I no longer trust my own reading of this code X-<. > diff --git a/http.c b/http.c > index 229da4d1488..2f67fbb33cd 100644 > --- a/http.c > +++ b/http.c > @@ -1367,6 +1367,7 @@ void run_active_slot(struct active_request_slot *slot) > select(max_fd+1, &readfds, &writefds, &excfds, &select_timeout); > } > } > + slot->finished = NULL; > } Will queue, but it would be nice if GCC can get fixed before we have to advance this to 'next' and below Thanks. .
