Module Name: src
Committed By: rillig
Date: Wed May 1 17:42:58 UTC 2024
Modified Files:
src/tests/usr.bin/xlint/lint1: decl.c
src/usr.bin/xlint/lint1: tree.c
Log Message:
lint: make 'offsetof(t, array-member)' a constant expression
The macro 'offsetof(t, m)' already expanded to a constant expression for
scalar members but not for arrays. This was because the macro expanded
to '(size_t)(((t *)0)->m)', which lint internally represents as
'addr(indir(ptr(0) + offset(m)))', and build_address simplifies
'addr(indir(x))' to 'x' if the types match. The types only match for
scalar types though, but not for arrays.
When build_address happens, the type information is incomplete,
therefore 'offsetof(t, array)' has to be simplified at a later point.
To generate a diff of this commit:
cvs rdiff -u -r1.29 -r1.30 src/tests/usr.bin/xlint/lint1/decl.c
cvs rdiff -u -r1.638 -r1.639 src/usr.bin/xlint/lint1/tree.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/tests/usr.bin/xlint/lint1/decl.c
diff -u src/tests/usr.bin/xlint/lint1/decl.c:1.29 src/tests/usr.bin/xlint/lint1/decl.c:1.30
--- src/tests/usr.bin/xlint/lint1/decl.c:1.29 Wed May 1 12:36:56 2024
+++ src/tests/usr.bin/xlint/lint1/decl.c Wed May 1 17:42:57 2024
@@ -1,4 +1,4 @@
-/* $NetBSD: decl.c,v 1.29 2024/05/01 12:36:56 rillig Exp $ */
+/* $NetBSD: decl.c,v 1.30 2024/05/01 17:42:57 rillig Exp $ */
# 3 "decl.c"
/*
@@ -243,22 +243,29 @@ get_x(struct point3d { struct point3d_nu
}
// Expressions of the form '(size_t)&null_ptr->member' are used by several
-// C implementations to implement the offsetof macro. Dereferencing a null
-// pointer invokes undefined behavior, though, even in this form.
+// C implementations to implement the offsetof macro.
void
offsetof_on_array_member(void)
{
- struct s1 {
+ typedef struct {
int padding, plain, arr[2];
- };
+ } s1;
+ // Bit-fields must have a constant number of bits.
struct s2 {
- unsigned int off_plain:(unsigned long)&((struct s1 *)0)->plain;
- // FIXME: offsetof must work for array members as well.
- /* expect+1: error: integral constant expression expected [55] */
- unsigned int off_arr:(unsigned long)&((struct s1 *)0)->arr;
- // FIXME: offsetof must work for array members as well.
- /* expect+1: error: integral constant expression expected [55] */
- unsigned int off_arr_element:(unsigned long)&((struct s1 *)0)->arr[0];
+ unsigned int off_plain:(unsigned long)&((s1 *)0)->plain;
+ unsigned int off_arr:(unsigned long)&((s1 *)0)->arr;
+ unsigned int off_arr_0:(unsigned long)&((s1 *)0)->arr[0];
+ unsigned int off_arr_3:(unsigned long)&((s1 *)0)->arr[3];
};
+
+ // Arrays may be variable-width, but the diagnostic reveals the size.
+ /* expect+1: error: negative array dimension (-4) [20] */
+ typedef int off_plain[-(int)(unsigned long)&((s1 *)0)->plain];
+ /* expect+1: error: negative array dimension (-8) [20] */
+ typedef int off_arr[-(int)(unsigned long)&((s1 *)0)->arr];
+ /* expect+1: error: negative array dimension (-8) [20] */
+ typedef int off_arr_0[-(int)(unsigned long)&((s1 *)0)->arr[0]];
+ /* expect+1: error: negative array dimension (-20) [20] */
+ typedef int off_arr_3[-(int)(unsigned long)&((s1 *)0)->arr[3]];
}
Index: src/usr.bin/xlint/lint1/tree.c
diff -u src/usr.bin/xlint/lint1/tree.c:1.638 src/usr.bin/xlint/lint1/tree.c:1.639
--- src/usr.bin/xlint/lint1/tree.c:1.638 Wed May 1 05:49:33 2024
+++ src/usr.bin/xlint/lint1/tree.c Wed May 1 17:42:57 2024
@@ -1,4 +1,4 @@
-/* $NetBSD: tree.c,v 1.638 2024/05/01 05:49:33 rillig Exp $ */
+/* $NetBSD: tree.c,v 1.639 2024/05/01 17:42:57 rillig Exp $ */
/*
* Copyright (c) 1994, 1995 Jochen Pohl
@@ -37,7 +37,7 @@
#include <sys/cdefs.h>
#if defined(__RCSID)
-__RCSID("$NetBSD: tree.c,v 1.638 2024/05/01 05:49:33 rillig Exp $");
+__RCSID("$NetBSD: tree.c,v 1.639 2024/05/01 17:42:57 rillig Exp $");
#endif
#include <float.h>
@@ -4112,6 +4112,28 @@ cast_to_union(tnode_t *otn, bool sys, ty
return NULL;
}
+// In GCC mode, allow 'nullptr + offset' as a constant expression.
+static tnode_t *
+null_pointer_offset(tnode_t *tn)
+{
+ uint64_t off = 0;
+ const tnode_t *n = tn;
+ while ((n->tn_op == PLUS || n->tn_op == MINUS)
+ && is_integer(n->u.ops.right->tn_type->t_tspec)) {
+ off += (uint64_t)n->u.ops.right->u.value.u.integer;
+ n = n->u.ops.left;
+ }
+ if (n->tn_type->t_tspec == PTR
+ && n->tn_op == ADDR
+ && n->u.ops.left->tn_op == INDIR
+ && n->u.ops.left->u.ops.left->tn_op == CON
+ && n->u.ops.left->u.ops.left->tn_type->t_tspec == PTR) {
+ off += (uint64_t)n->u.ops.left->u.ops.left->u.value.u.integer;
+ return build_integer_constant(SIZEOF_TSPEC, (int64_t)off);
+ }
+ return tn;
+}
+
tnode_t *
cast(tnode_t *tn, bool sys, type_t *tp)
{
@@ -4144,7 +4166,7 @@ cast(tnode_t *tn, bool sys, type_t *tp)
error(148);
return NULL;
} else if (is_integer(nt) && is_scalar(ot)) {
- /* ok */
+ tn = null_pointer_offset(tn);
} else if (is_floating(nt) && is_arithmetic(ot)) {
/* ok */
} else if (nt == PTR && is_integer(ot)) {
