| Summary: | Missed -Wreturn-local-addr when local variable address comes from within a statement expression | ||
|---|---|---|---|
| Product: | gcc | Reporter: | Andrew Gaul <gcc> |
| Component: | c | Assignee: | Not yet assigned to anyone <unassigned> |
| Status: | NEW --- | ||
| Severity: | minor | CC: | dmalcolm, dodji, egallager, manu, philiprbrenan |
| Priority: | P3 | Keywords: | diagnostic, stmt-expr |
| Version: | unknown | ||
| Target Milestone: | --- | ||
| Host: | Target: | ||
| Build: | Known to work: | ||
| Known to fail: | Last reconfirmed: | 2015-09-18 00:00:00 | |
| Bug Depends on: | 60517 | ||
| Bug Blocks: | 772, 90556 | ||
| Attachments: |
example of bug
example of bug 2 example of bug 3 |
||
Created attachment 21905 [details] example of bug 2 Created attachment 21906 [details] example of bug 3 The web form truncates all my attachedments at 244 bytes. Here is the source inline:
/*
* GCC warns about returning a local variable address within a function but not
* within a statement expression:
*
* $ gcc statement_expression_return_local.c -c -Wall
* statement_expression_return_local.c: In function ‘function_return_local’:
* statement_expression_return_local.c:13: warning: function returns address of local variable
*/
int *function_return_local(void)
{
int x = 0;
return &x;
}
int *statement_expression_return_local(void)
{
int *y = ({
int x = 0;
&x;
});
return y;
}
(In reply to Andrew Gaul from comment #3) > int *function_return_local(void) > { > int x = 0; > return &x; > } > > int *statement_expression_return_local(void) > { > int *y = ({ > int x = 0; > &x; > }); > return y; > } We now warn at -O2: test.c:14:10: warning: function returns address of local variable [-Wreturn-local-addr] return y; ^ test.c:11:11: note: declared here int x = 0; ^ but only because we return y. For this testcase, int statement_expression_return_local(void) { int *y = ({ int x = 0; &x; }); return *y; } we get: test.c:14:10: warning: ‘x’ is used uninitialized in this function [-Wuninitialized] return *y; ^ which is a bit confusing (and not the same warning). Possibly related to 60517. it would be good to add the testcase cc-ing diagnostic messages maintainers (In reply to Manuel López-Ibáñez from comment #4) > (In reply to Andrew Gaul from comment #3) > > int *function_return_local(void) > > { > > int x = 0; > > return &x; > > } > > > > int *statement_expression_return_local(void) > > { > > int *y = ({ > > int x = 0; > > &x; > > }); > > return y; > > } > > We now warn at -O2: > > test.c:14:10: warning: function returns address of local variable > [-Wreturn-local-addr] > return y; > ^ > test.c:11:11: note: declared here > int x = 0; > ^ > > but only because we return y. For this testcase, > > int statement_expression_return_local(void) > { > int *y = ({ > int x = 0; > &x; > }); > return *y; > } > > we get: > > test.c:14:10: warning: ‘x’ is used uninitialized in this function > [-Wuninitialized] > return *y; > ^ > > which is a bit confusing (and not the same warning). It'd be good to get it from the same warning, so I'm making this block the -Wreturn-local-addr meta-bug > > Possibly related to 60517. > it would be good to add the testcase A more compact example:
#include <stdio.h>
int * aaa() {return ({int a = 2; &a;});} // no warning unless -O2
int * bbb() { int b = 3; return &b;} // warning
int main(void)
{int *a = aaa(), *b = bbb();
fprintf(stderr, "AAAA %d\n", *a);
fprintf(stderr, "BBBB %d\n", *b);
return 0;
}
// AAAA 3
// Segmentation fault (core dumped)
Please provide the warning for line 2 (aaa) regardless of the level of optimization?
|
Created attachment 21904 [details] example of bug GCC warns when returning a local variable address within a function but not within a statement expression.