[Bug middle-end/99098] invalid/missing -Wfree-nonheap-object warnings
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99098 --- Comment #5 from Peter Ross --- The -1 occurs after checking the malloc()==0 case, so the negative offset is only ever applied to addresses in [1..limit] range. Thanks for your time!
[Bug middle-end/99098] invalid/missing -Wfree-nonheap-object warnings
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99098 --- Comment #4 from Andrew Pinski --- (In reply to Peter Ross from comment #2) > The following test case produces a -Wfree-nonheap-object false positive. I > argue that the memory being free'd is heap memory. It is offset by one to > accomodate the negative offset applied immediately after malloc. Doing -1 on an allocated memory location is undefined because you can only have the address of 0...size to be taken of the "object" according to the C standard. So the warning might seem wrong but you have undefined code happening.
[Bug middle-end/99098] invalid/missing -Wfree-nonheap-object warnings
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99098 --- Comment #3 from Peter Ross --- Created attachment 55814 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=55814=edit Test case -save-temps output
[Bug middle-end/99098] invalid/missing -Wfree-nonheap-object warnings
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99098
Peter Ross changed:
What|Removed |Added
CC||pross at xvid dot org
--- Comment #2 from Peter Ross ---
The following test case produces a -Wfree-nonheap-object false positive. I
argue that the memory being free'd is heap memory. It is offset by one to
accomodate the negative offset applied immediately after malloc.
```
#include
char * knn_alloc()
{
char * w = malloc(sizeof(char));
if (!w)
return NULL;
return w - 1;
}
void knn_free(char * w)
{
free(w + 1);
}
int main()
{
char * w = knn_alloc();
if (!w)
return -1;
knn_free(w);
return 0;
}
```
```
$ gcc knn.c -save-temps
knn.c: In function ‘knn_free’:
knn.c:11:5: warning: ‘free’ called on pointer ‘w’ with nonzero offset 1
[-Wfree-nonheap-object]
11 | free(w + 1);
| ^~~
```
gcc --version: gcc (Debian 13.2.0-2) 13.2.0
uname -a: Linux computer 6.4.0-3-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.4.11-1
(2023-08-17) x86_64 GNU/Linux
[Bug middle-end/99098] invalid/missing -Wfree-nonheap-object warnings
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99098 Bug 99098 depends on bug 93873, which changed state. Bug 93873 Summary: gcc or lto-wrapper does not consider individual bitfield values on static analysis and instead tests the whole value of all bitfield bits combined https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93873 What|Removed |Added Status|UNCONFIRMED |RESOLVED Resolution|--- |FIXED
[Bug middle-end/99098] invalid/missing -Wfree-nonheap-object warnings
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99098 Martin Sebor changed: What|Removed |Added Ever confirmed|0 |1 Alias||Wfree-nonheap-object Last reconfirmed||2021-02-14 Version|11.0|4.7.0 Status|UNCONFIRMED |NEW Keywords||diagnostic, meta-bug --- Comment #1 from Martin Sebor --- -Wfree-nonheap-object was introduced in r178004 (in GCC 4.7.0).
