https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107289
Bug ID: 107289
Summary: - -Wanayzer-null-dereference false positive with f =
*b
Product: gcc
Version: 12.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: analyzer
Assignee: dmalcolm at gcc dot gnu.org
Reporter: geoffreydgr at icloud dot com
Target Milestone: ---
I got a false positive error when compiling the following "minimal, complete
and verifiable example (MCVE)" program
```
int a=1;
int *b = &a;
void c () {
int f;
f = *b;
}
void e(){
if (0 == b){
int *g = 0;
}
}
void d() { e(); c();}
int main(){
d();
}
```
Compiling the above code with gcc 12.1 with `-O0 -fanalyzer` in
https://godbolt.org/ results in :
```
<source>: In function 'void c()':
<source>:5:7: warning: dereference of NULL 'b' [CWE-476]
[-Wanalyzer-null-dereference]
5 | f = *b;
| ~~^~~~
'void d()': events 1-2
|
| 12 | void d() { e(); c();}
| | ^ ~~~
| | | |
| | | (2) calling 'e' from 'd'
| | (1) entry to 'd'
|
+--> 'void e()': events 3-6
|
| 7 | void e(){
| | ^
| | |
| | (3) entry to 'e'
| 8 | if (0 == b){
| | ~~
| | |
| | (4) following 'true' branch...
| 9 | int *g = 0;
| | ~
| | |
| | (5) ...to here
| | (6) 'b' is NULL
|
<------+
|
'void d()': events 7-8
|
| 12 | void d() { e(); c();}
| | ~^~ ~~~
| | | |
| | | (8) calling 'c' from 'd'
| | (7) returning to 'd' from 'e'
|
+--> 'void c()': events 9-10
|
| 3 | void c () {
| | ^
| | |
| | (9) entry to 'c'
| 4 | int f;
| 5 | f = *b;
| | ~~~~~~
| | |
| | (10) dereference of NULL 'b'
```
It should not be a null pointer deference, because b is a pointer to a. GCC
seems to be fooled by line 8 if (0 == b){...}. But if I change the example
program to the following one, the false positive error disappears:
```
int a=1;
int *b = &a;
void c () {
int f;
f = *b;
}
void d() { c();}
int main(){
if (0 == b){
int *g = 0;
}
d();
}
```
