| Summary: | warn for read-only uninitialized variables passed as arguments | ||
|---|---|---|---|
| Product: | gcc | Reporter: | Manuel López-Ibáñez <manu> |
| Component: | middle-end | Assignee: | Not yet assigned to anyone <unassigned> |
| Status: | RESOLVED DUPLICATE | ||
| Severity: | enhancement | CC: | gcc-bugs, manu, msebor, pinskia |
| Priority: | P3 | ||
| Version: | 4.3.0 | ||
| Target Milestone: | --- | ||
| Host: | Target: | ||
| Build: | Known to work: | ||
| Known to fail: | Last reconfirmed: | ||
| Bug Depends on: | |||
| Bug Blocks: | 10138 | ||
> At least for languages where 'const' is actually enforced
There is none, unless you are taking about fortran "in" arguments. So we need to mark such argument as special.
Now if you have the full program (or at least the containts of use function), and you can prove it never writes to the incoming pointer argument, then you can warn but only then.
In C and C++ you can never tell without the body of use.
(In reply to comment #1) > > At least for languages where 'const' is actually enforced > > There is none, void use(const int *a) { a[0] = 5; } void foo(void) { int i; use(&i); } new.c:3: error: assignment of read-only location Either I am misunderstanding you or your argument about overwriting the pointer argument is equivalent to just don't using the value of 'i'. Of course, we don't know whether the value is used or not within use() but the fact is that 'i' cannot be initialized within use().
void use(const int *a)
{
int *b = (int*)a;
b[0] = 5;
}
void foo(void)
{
int i;
use(&i);
}
(In reply to comment #3) > > void use(const int *a) > { > int *b = (int*)a; Andrew, you are right. I tend to forget how fragile is 'const', even in C++. So, then this is invalid and thus it is PR10138. Andrew, what about functions marked with attribute "pure" ? int atoi(const char *) __attribute__ ((pure)); I think it would be reasonable to issue a warning on the code in comment #3 (perhaps under -Wmaybe-uninitialized rather than -Wuninitialized). For uninitialized variables passed by reference to pure functions (that cannot change objects pointed to by their arguments) I think it would make sense to issue -Wunitialized. Based on comment #4 and on my understanding of the two reports resolving as a duplicate of bug 10138. *** This bug has been marked as a duplicate of bug 10138 *** |
void use(const int *); void foo(void) { int i; use(&i); } At least for languages where 'const' is actually enforced, we should warn for this. For languages where the 'const' can be cast away and 'i' can be initialized by 'use' the situation is less clear (although personally I think we should warn anyway). This is one part of PR10138. "the question whether an argument is actually used or not is secondary, the fact that we pass an uninitialized variable to which only read access is possible is definitely worth a warning." http://gcc.gnu.org/bugzilla/show_bug.cgi?id=10138#c8