[Bug middle-end/109557] __builtin_dynamic_object_size() does not work for simple testing case
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109557
--- Comment #8 from qinzhao at gcc dot gnu.org ---
with the following slightly modified testing case, the same issue:
#include
#include
struct P {
int k;
int x[10];
} *p;
void store(int a, int b)
{
p = (struct P *)malloc (sizeof (struct P));
p->k = a;
p->x[b] = 0;
assert (__builtin_dynamic_object_size (p, 1) == sizeof (struct P));
return;
}
int main()
{
store(7, 7);
assert (__builtin_dynamic_object_size (p, 1) == sizeof (struct P));
free (p);
}
[opc@qinzhao-ol8u3-x86 109557]$ sh t
/home/opc/Install/latest/bin/gcc -O -fsanitize=bounds -fsanitize=object-size
-fstrict-flex-arrays=3 -fdump-tree-all t.c
a.out: t.c:20: main: Assertion `__builtin_dynamic_object_size (p, 1) == sizeof
(struct P)' failed.
t: line 19: 629958 Aborted (core dumped) ./a.out
[Bug middle-end/109557] __builtin_dynamic_object_size() does not work for simple testing case
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109557 --- Comment #7 from qinzhao at gcc dot gnu.org --- Okay, thanks for the comment. I see why this should not work.
[Bug middle-end/109557] __builtin_dynamic_object_size() does not work for simple testing case
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109557 Siddhesh Poyarekar changed: What|Removed |Added Status|UNCONFIRMED |RESOLVED Resolution|--- |INVALID --- Comment #6 from Siddhesh Poyarekar --- (In reply to Martin Uecker from comment #5) > With "in general" I meant in a different program. From just knowing the > type of the pointer you can not derive the object size. This is how I > understood the original question. Ah ok, agreed. Closing this as invalid then; I noticed I was missing the inline keyword when I tried forcing inlining, so that was also a PEBKAC.
[Bug middle-end/109557] __builtin_dynamic_object_size() does not work for simple testing case
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109557 --- Comment #5 from Martin Uecker --- (In reply to Siddhesh Poyarekar from comment #4) > (In reply to Martin Uecker from comment #3) > > I general the pointer could point to the first object of an array that has > > more elements, or to an object of a different type. > > How so? p in comment 0 is just a NULL-initialized pointer. It gets > assigned to a malloc'd storage in store() (which the code in main() cannot > see) but until then, it's a NULL pointer. With "in general" I meant in a different program. From just knowing the type of the pointer you can not derive the object size. This is how I understood the original question.
[Bug middle-end/109557] __builtin_dynamic_object_size() does not work for simple testing case
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109557 --- Comment #4 from Siddhesh Poyarekar --- (In reply to Martin Uecker from comment #3) > I general the pointer could point to the first object of an array that has > more elements, or to an object of a different type. How so? p in comment 0 is just a NULL-initialized pointer. It gets assigned to a malloc'd storage in store() (which the code in main() cannot see) but until then, it's a NULL pointer.
[Bug middle-end/109557] __builtin_dynamic_object_size() does not work for simple testing case
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109557 Martin Uecker changed: What|Removed |Added CC||muecker at gwdg dot de --- Comment #3 from Martin Uecker --- I general the pointer could point to the first object of an array that has more elements, or to an object of a different type. The semantics of C are not strong enough here, but it would be good to have some kind of annotation for the pointer that would allow this.
[Bug middle-end/109557] __builtin_dynamic_object_size() does not work for simple testing case
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109557 --- Comment #2 from Siddhesh Poyarekar --- (In reply to qinzhao from comment #0) > I am wondering for > p.3_1 = p; > _2 = __builtin_object_size (p.3_1, 0); > > why the size of p.3_1 cannot use the TYPE_SIZE of the pointee of p when its > size can be determined (i.e, not a structure with a flexible array member, > etc)? To answer this specific question, it's because the compiler can't see in main() if p is pointing to any actual storage.
[Bug middle-end/109557] __builtin_dynamic_object_size() does not work for simple testing case
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109557 --- Comment #1 from Siddhesh Poyarekar --- The __bdos call itself cannot succeed in main() because it cannot see the allocation in store(). One way it could succeed is if store() was inlined, but for some reason it doesn't, even if you make the function static inline. If I decorate store() with __attribute__((inline)) I get the warning: foo.c:10:1: warning: ‘always_inline’ function might not be inlinable [-Wattributes] but it seems to proceed to inline the call because the assert in main() is no longer hit. So from the __bdos context I'm inclined to say NOTABUG.
