https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94815
Martin Sebor <msebor at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|--- |WONTFIX
Status|NEW |RESOLVED
--- Comment #2 from Martin Sebor <msebor at gcc dot gnu.org> ---
The warning is only issued with optimization enabled the strlen pass disabled,
such as at -O1, but not at -O2. The strlen dump below helps explain why: when
the strlen pass doesn't run the warning doesn't compute the length of str2 (as
reflected by the very large value in the Result of the %s directive) and so it
makes a decision solely on the basis that the %s argument points to the same
array as the destination of the sprintf call. This is by design. To avoid
the warning under these conditions use a precision in the directive: %.3s.
;; Function f (f, funcdef_no=0, decl_uid=1938, cgraph_uid=1, symbol_order=0)
;; 1 loops found
;;
;; Loop 0
;; header 0, latch 1
;; depth 0, outer -1
;; nodes: 0 1 2
;; 2 succs { 1 }
Computing maximum subobject size for buf_3:
pr94815.c:13: sprintf: objsize = 9223372036854775807, fmtstr = "ABC%s"
Directive 1 at offset 0: "ABC", length = 3
Result: 3, 3, 3, 3 (3, 3, 3, 3)
Directive 2 at offset 3: "%s"
Result: 0, 0, -1, 9223372036854775807 (3, 3, -1, -1)
Directive 3 at offset 5: "", length = 1
pr94815.c: In function ‘f’:
pr94815.c:13:5: warning: ‘sprintf’ argument 3 may overlap destination object
‘buf’ [-Wrestrict]
13 | sprintf(str1, "ABC%s", str2);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
