| Issue |
128531
|
| Summary |
[clang] No warning for a memcpy from an uninitialized local variable
|
| Labels |
clang
|
| Assignees |
|
| Reporter |
isbadawi
|
I encountered a bug that boiled down to something like this, passing the address of an uninitialized local variable as the source for memcpy:
```c
#include <string.h>
void foo(int *out) {
int x;
memcpy(out, &x, sizeof(x));
}
```
The bug was only discovered after upgrading to a more recent clang happened to expose a runtime issue, there was no diagnostic. I found that latest gcc warns about this, but latest clang doesn't, see https://godbolt.org/z/7rd84W7sc
Output from gcc 14.2
```
<source>: In function 'main':
<source>:7:3: warning: 'x' is used uninitialized [-Wuninitialized]
7 | memcpy(&y, &x, sizeof(x));
| ^~~~~~~~~~~~~~~~~~~~~~~~~
<source>:4:7: note: 'x' declared here
4 | int x;
|
```
It seems like gcc also more generally emits either `-Wuninitialized` or `-Wmaybe-uninitialized` when passing pointers to uninitialized local variables to functions, which is partly driven by parameters marked `const` or annotated using attribute `access`, but at least the memcpy case seems like it would be useful to cover.
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