[Bug c++/49974] missing -Wreturn-local-addr for indirectly returning reference to local/temporary
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=49974
--- Comment #20 from Andrew Pinski ---
(In reply to Barry Revzin from comment #19)
> Another example of this:
>
> int get();
>
> int const& f() {
> int const r = get();
> return r;
> }
>
> int const& g() {
> int const& r = get();
> return r;
> }
>
> gcc trunk warns on the incorrect use in f, but it does not currently warn on
> the incorrect use in g (which is the exact same bug). clang warns on both.
GCC trunk does warn on g but only with optimizations turned on.
[Bug c++/49974] missing -Wreturn-local-addr for indirectly returning reference to local/temporary
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=49974
Barry Revzin changed:
What|Removed |Added
CC||barry.revzin at gmail dot com
--- Comment #19 from Barry Revzin ---
Another example of this:
int get();
int const& f() {
int const r = get();
return r;
}
int const& g() {
int const& r = get();
return r;
}
gcc trunk warns on the incorrect use in f, but it does not currently warn on
the incorrect use in g (which is the exact same bug). clang warns on both.
[Bug c++/49974] missing -Wreturn-local-addr for indirectly returning reference to local/temporary
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=49974
--- Comment #18 from Martin Sebor ---
This detection is partially implemented in GCC 12 by the -Wdnagling-pointer:
$ cat pr49974.C && gcc -O -S -Wall pr49974.C
struct X { };
inline const X& f(const X& r) { return r; }
const X& g()
{
X x;
return f(x); // !!!
}
const X& h()
{
return f(X()); // !!!
}
struct Y {
Y(int& i) : r(i) { }
int& r;
};
Y f()
{
int i=0;
return Y(i);
}
pr49974.C: In function ‘const X& g()’:
pr49974.C:9:15: warning: using a dangling pointer to ‘x’ [-Wdangling-pointer=]
9 | return f(x); // !!!
| ^
pr49974.C:8:7: note: ‘x’ declared here
8 | X x;
| ^
pr49974.C: In function ‘const X& h()’:
pr49974.C:14:17: warning: using a dangling pointer to an unnamed temporary
[-Wdangling-pointer=]
14 | return f(X()); // !!!
| ^
pr49974.C:14:16: note: unnamed temporary defined here
14 | return f(X()); // !!!
|^
For the test case in comment #17 GCC with -O1 issues:
pr49974-c17.C: In function ‘int main()’:
pr49974-c17.C:11:12: warning: using a dangling pointer to an unnamed temporary
[-Wdangling-pointer=]
11 | return x.i;
|^
pr49974-c17.C:10:15: note: unnamed temporary defined here
10 | X&& x = f(X{});
| ^
pr49974-c17.C:11:12: warning: ‘.X::i’ is used uninitialized
[-Wuninitialized]
11 | return x.i;
|^
pr49974-c17.C:10:15: note: ‘’ declared here
10 | X&& x = f(X{});
| ^
[Bug c++/49974] missing -Wreturn-local-addr for indirectly returning reference to local/temporary
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=49974
--- Comment #17 from Jonathan Wakely ---
95911 boils down to this:
#include
struct X { int i = 0; };
X&& f(X&& x) { return std::move(x); }
int main()
{
X&& x = f(X{});
return x.i;
}
With recent releases we get a -Wuninitialized warning, which isn't entirely
correct, but at least suggests a problem:
49974.cc: In function 'int main()':
49974.cc:10:12: warning: '.X::i' is used uninitialized
[-Wuninitialized]
10 | return x.i;
|^
49974.cc:9:15: note: '' declared here
9 | X&& x = f(X{});
| ^
(the note is new in GCC 11).
With -fsanitize=address we get a nice stack-use-after-scope error:
==3088273==ERROR: AddressSanitizer: stack-use-after-scope on address
0x7fff976ed520 at pc 0x00401100 bp 0x7fff976ed4f0 sp 0x7fff976ed4e8
READ of size 4 at 0x7fff976ed520 thread T0
#0 0x4010ff in main /tmp/49974.cc:10
#1 0x7fd157d181a2 in __libc_start_main ../csu/libc-start.c:308
#2 0x40116d in _start (/tmp/a.out+0x40116d)
[Bug c++/49974] missing -Wreturn-local-addr for indirectly returning reference to local/temporary
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=49974 Jonathan Wakely changed: What|Removed |Added CC||570070308 at qq dot com --- Comment #16 from Jonathan Wakely --- *** Bug 95911 has been marked as a duplicate of this bug. ***
[Bug c++/49974] missing -Wreturn-local-addr for indirectly returning reference to local/temporary
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=49974 Martin Sebor changed: What|Removed |Added CC||msebor at gcc dot gnu.org See Also||https://gcc.gnu.org/bugzill ||a/show_bug.cgi?id=90905 --- Comment #15 from Martin Sebor --- GCC 10 issues two warnings for the first test case in comment #0: pr49974.C: In function ‘const X& g()’: pr49974.C:8:15: warning: function returns address of local variable [-Wreturn-local-addr] 8 | return f(x); // !!! | ^ pr49974.C:7:7: note: declared here 7 | X x; | ^ In function ‘const X& h()’: cc1plus: warning: function returns address of local variable [-Wreturn-local-addr] pr49974.C:7:7: note: declared here The second test case is not diagnosed (due to a similar problem as pr90905). The test cases in comment #8 are also not diagnosed.
[Bug c++/49974] missing -Wreturn-local-addr for indirectly returning reference to local/temporary
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=49974 Eric Gallager changed: What|Removed |Added Summary|missing warning for |missing -Wreturn-local-addr |indirectly returning|for indirectly returning |reference to|reference to |local/temporary |local/temporary --- Comment #14 from Eric Gallager --- (In reply to Jonathan Wakely from comment #13) > Yes, I think so. The bug is returning a reference (indirectly) bound to a > local, so I don't see a reason to have a different warning. ok, updating title
