[Bug middle-end/109990] [12/13/14 Regression] Bogus -Wuse-after-free warning after realloc
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109990 Jeffrey A. Law changed: What|Removed |Added Priority|P3 |P2
[Bug middle-end/109990] [12/13/14 Regression] Bogus -Wuse-after-free warning after realloc
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109990 Jeffrey A. Law changed: What|Removed |Added Last reconfirmed||2024-03-10 CC||law at gcc dot gnu.org Status|UNCONFIRMED |NEW Ever confirmed|0 |1
[Bug middle-end/109990] [12/13/14 Regression] Bogus -Wuse-after-free warning after realloc
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109990 Richard Biener changed: What|Removed |Added Target Milestone|--- |12.4
[Bug middle-end/109990] [12/13/14 Regression] Bogus -Wuse-after-free warning after realloc
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109990 --- Comment #6 from Andrew Pinski --- (In reply to Bruno Haible from comment #4) > That is the only way of keeping track of pointers _into_ the string_space > area, when it is reallocated. How else would you want to do it? You could use intptr_t casting to do the subtraction ...
[Bug middle-end/109990] [12/13/14 Regression] Bogus -Wuse-after-free warning after realloc
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109990 --- Comment #5 from Bruno Haible --- Created attachment 55170 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=55170=edit test case bar2.c Find attached a modified test case. I changed the code to map[i].alias = new_pool + (map[i].alias - string_space); map[i].value = new_pool + (map[i].value - string_space); so that it subtracts pointers into the old string_space, producing an integer, and adding that integer to new_pool. It produces the same warning (even twice, apparently because there is no common subexpression between the two lines any more): $ gcc -Wall -O2 -S bar2.c bar2.c: In function ‘read_alias_file’: bar2.c:123:67: warning: pointer may be used after ‘realloc’ [-Wuse-after-free] 123 | map[i].value = new_pool + (map[i].value - string_space); | ~~^~~ bar2.c:114:45: note: call to ‘realloc’ here 114 | char *new_pool = (char *) realloc (string_space, new_size); | ^~~~ bar2.c:122:67: warning: pointer may be used after ‘realloc’ [-Wuse-after-free] 122 | map[i].alias = new_pool + (map[i].alias - string_space); | ~~^~~ bar2.c:114:45: note: call to ‘realloc’ here 114 | char *new_pool = (char *) realloc (string_space, new_size); | ^~~~
[Bug middle-end/109990] [12/13/14 Regression] Bogus -Wuse-after-free warning after realloc
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109990
--- Comment #4 from Bruno Haible ---
> >
> > char *new_pool = (char *) realloc (string_space,
> > new_size);
> > if (new_pool == ((void *)0))
> > goto out;
> > if (__builtin_expect (string_space != new_pool, 0))
> > {
> > size_t i;
> > for (i = 0; i < nmap; i++)
> > {
> > map[i].alias += new_pool - string_space;
> > map[i].value += new_pool - string_space;
> > }
> > }
> > string_space = new_pool;
> Also I think `new_pool - string_space` is undefined really. That is
> subtracting two unrelated arrays is undefined. You can only compare equality
> on them.
That is the only way of keeping track of pointers _into_ the string_space area,
when it is reallocated. How else would you want to do it?
[Bug middle-end/109990] [12/13/14 Regression] Bogus -Wuse-after-free warning after realloc
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109990
--- Comment #3 from Andrew Pinski ---
(In reply to Andrew Pinski from comment #1)
> ```
>
> char *new_pool = (char *) realloc (string_space, new_size);
> if (new_pool == ((void *)0))
> goto out;
> if (__builtin_expect (string_space != new_pool, 0))
> {
> size_t i;
> for (i = 0; i < nmap; i++)
> {
> map[i].alias += new_pool - string_space;
> map[i].value += new_pool - string_space;
> }
> }
> string_space = new_pool;
> ```
>
> Hmmm
Also I think `new_pool - string_space` is undefined really. That is
subtracting two unrelated arrays is undefined. You can only compare equality on
them.
[Bug middle-end/109990] [12/13/14 Regression] Bogus -Wuse-after-free warning after realloc
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109990 Andrew Pinski changed: What|Removed |Added See Also||https://gcc.gnu.org/bugzill ||a/show_bug.cgi?id=104215 --- Comment #2 from Andrew Pinski --- See also the discussion starting at bug 104215 comment #2.
[Bug middle-end/109990] [12/13/14 Regression] Bogus -Wuse-after-free warning after realloc
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109990
--- Comment #1 from Andrew Pinski ---
```
char *new_pool = (char *) realloc (string_space, new_size);
if (new_pool == ((void *)0))
goto out;
if (__builtin_expect (string_space != new_pool, 0))
{
size_t i;
for (i = 0; i < nmap; i++)
{
map[i].alias += new_pool - string_space;
map[i].value += new_pool - string_space;
}
}
string_space = new_pool;
```
Hmmm
