https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106939
Bug ID: 106939
Summary: Linker-defined symbols are stained due to 'array
subscript is partly outside array bounds' warning
Product: gcc
Version: 12.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: neoxic at icloud dot com
Target Milestone: ---
Working with embedded applications, one often deals with manipulating memory
regions via symbols defined in a linker script. Please consider the following
snippet:
-----------------------------------------------------
#include <string.h>
extern char _src, _dst; // Defined by the linker
int main(void) {
memcpy(&_dst, &_src + 1024, 1111);
return 0;
}
-----------------------------------------------------
Compilation with GCC 12.2.0 yields lots of warnings:
-----------------------------------------------------
$ cc -O2 -Wall -Wextra -fno-strict-aliasing -fwrapv a.c
a.c: In function ‘main’:
a.c:6:29: warning: array subscript 1024 is outside array bounds of ‘char[1]’
[-Warray-bounds]
6 | memcpy(&_dst, &_src + 1024, 1111);
| ~~~~~~^~~~~~
a.c:3:13: note: at offset 1024 into object ‘_src’ of size 1
3 | extern char _src, _dst; // Defined by the linker
| ^~~~
a.c:6:9: warning: ‘memcpy’ forming offset [1, 1110] is out of the bounds [0, 1]
of object ‘_dst’ with type ‘char’ [-Warray-bounds]
6 | memcpy(&_dst, &_src + 1024, 1111);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
a.c:3:19: note: ‘_dst’ declared here
3 | extern char _src, _dst; // Defined by the linker
| ^~~~
-----------------------------------------------------
These symbols are used as mere address anchors, they don't contain anything.
But no matter what I do like changing their type, casting their addresses, etc,
I can't get rid of the pesky sticky warnings now. Is there a clean way to work
around these warning without turning off Warray-bounds?
