[src/trunk]: src/usr.bin/xlint/lint1 lint: fix computation of bit-field width

[rillig <rillig%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/45f343f193db
branches:  trunk
changeset: 377187:45f343f193db
user:      rillig <rillig%NetBSD.org@localhost>
date:      Fri Jun 30 15:19:09 2023 +0000

description:
lint: fix computation of bit-field width

When bit-fields in packed structs were added on 2009-10-02, lint assumed
that they would only use 'signed int' or 'unsigned int' as storage unit,
even though C99 also allows _Bool.

The cleanup commit for decl.c 1.225 from 2021-08-28 accidentally changed
the rounding mode for bit-field storage units from round-up to
round-down.

diffstat:

 tests/usr.bin/xlint/lint1/expr_sizeof.c |   4 +-
 tests/usr.bin/xlint/lint1/msg_065.c     |   4 +-
 usr.bin/xlint/lint1/decl.c              |  34 ++++++++++++++++++--------------
 3 files changed, 23 insertions(+), 19 deletions(-)

diffs (127 lines):

diff -r e92cd2195cc0 -r 45f343f193db tests/usr.bin/xlint/lint1/expr_sizeof.c
--- a/tests/usr.bin/xlint/lint1/expr_sizeof.c   Fri Jun 30 14:39:23 2023 +0000
+++ b/tests/usr.bin/xlint/lint1/expr_sizeof.c   Fri Jun 30 15:19:09 2023 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: expr_sizeof.c,v 1.9 2023/06/30 09:21:52 rillig Exp $   */
+/*     $NetBSD: expr_sizeof.c,v 1.10 2023/06/30 15:19:09 rillig Exp $  */
 # 3 "expr_sizeof.c"
 
 /*
@@ -92,7 +92,7 @@ bit_fields(void)
                        _Bool flag2:1;
                };
        } anonymous_flags;
-       /* FIXME: sizeof must be 1, not 0. */
+       /* expect+1: error: negative array dimension (-1) [20] */
        typedef int sizeof_anonymous_flags[-(int)sizeof(anonymous_flags)];
 
        struct {
diff -r e92cd2195cc0 -r 45f343f193db tests/usr.bin/xlint/lint1/msg_065.c
--- a/tests/usr.bin/xlint/lint1/msg_065.c       Fri Jun 30 14:39:23 2023 +0000
+++ b/tests/usr.bin/xlint/lint1/msg_065.c       Fri Jun 30 15:19:09 2023 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: msg_065.c,v 1.4 2022/06/22 19:23:18 rillig Exp $       */
+/*     $NetBSD: msg_065.c,v 1.5 2023/06/30 15:19:09 rillig Exp $       */
 # 3 "msg_065.c"
 
 // Test for message: '%s' has no named members [65]
@@ -7,7 +7,7 @@ struct ok {
        int member;
 };
 
-/* XXX: should generate a warning as well. */
+/* Don't warn about completely empty structs, which are a GCC extension. */
 struct empty {
 };
 
diff -r e92cd2195cc0 -r 45f343f193db usr.bin/xlint/lint1/decl.c
--- a/usr.bin/xlint/lint1/decl.c        Fri Jun 30 14:39:23 2023 +0000
+++ b/usr.bin/xlint/lint1/decl.c        Fri Jun 30 15:19:09 2023 +0000
@@ -1,4 +1,4 @@
-/* $NetBSD: decl.c,v 1.325 2023/06/30 14:39:23 rillig Exp $ */
+/* $NetBSD: decl.c,v 1.326 2023/06/30 15:19:09 rillig Exp $ */
 
 /*
  * Copyright (c) 1996 Christopher G. Demetriou.  All Rights Reserved.
@@ -38,7 +38,7 @@
 
 #include <sys/cdefs.h>
 #if defined(__RCSID)
-__RCSID("$NetBSD: decl.c,v 1.325 2023/06/30 14:39:23 rillig Exp $");
+__RCSID("$NetBSD: decl.c,v 1.326 2023/06/30 15:19:09 rillig Exp $");
 #endif
 
 #include <sys/param.h>
@@ -456,18 +456,20 @@ set_first_typedef(type_t *tp, sym_t *sym
 }
 
 static unsigned int
-bit_field_width(sym_t **mem)
+bit_field_width(sym_t **mem, bool *named)
 {
-       unsigned int width = (*mem)->s_type->t_bit_field_width;
+       unsigned int width = 0;
+       unsigned int align = 0;
        while (*mem != NULL && (*mem)->s_type->t_bitfield) {
+               if ((*mem)->s_name != unnamed)
+                       *named = true;
                width += (*mem)->s_type->t_bit_field_width;
+               unsigned int mem_align = alignment_in_bits((*mem)->s_type);
+               if (mem_align > align)
+                       align = mem_align;
                *mem = (*mem)->s_next;
        }
-
-       // XXX: Why INT_SIZE? C99 6.7.2.1p4 allows bit-fields to have type
-       // XXX: _Bool or another implementation-defined type.
-       // XXX: Why round down instead of up? See expr_sizeof.c, anonymous_flags.
-       return width - width % INT_SIZE;
+       return (width + align - 1) & -align;
 }
 
 static void
@@ -481,11 +483,12 @@ pack_struct_or_union(type_t *tp)
        }
 
        unsigned int bits = 0;
+       bool named = false;
        for (sym_t *mem = tp->t_sou->sou_first_member;
             mem != NULL; mem = mem->s_next) {
                // TODO: Maybe update mem->u.s_member.sm_offset_in_bits.
                if (mem->s_type->t_bitfield) {
-                       bits += bit_field_width(&mem);
+                       bits += bit_field_width(&mem, &named);
                        if (mem == NULL)
                                break;
                }
@@ -1795,24 +1798,25 @@ complete_struct_or_union(sym_t *first_me
                c99ism(47, tspec_name(tp->t_tspec));
        }
 
-       int n = 0;
+       bool has_named_member = false;
        for (sym_t *mem = first_member; mem != NULL; mem = mem->s_next) {
+               if (mem->s_name != unnamed)
+                       has_named_member = true;
                /* bind anonymous members to the structure */
                if (mem->u.s_member.sm_sou_type == NULL) {
                        mem->u.s_member.sm_sou_type = sp;
                        if (mem->s_type->t_bitfield) {
-                               sp->sou_size_in_bits += bit_field_width(&mem);
+                               sp->sou_size_in_bits +=
+                                   bit_field_width(&mem, &has_named_member);
                                if (mem == NULL)
                                        break;
                        }
                        sp->sou_size_in_bits +=
                            type_size_in_bits(mem->s_type);
                }
-               if (mem->s_name != unnamed)
-                       n++;
        }
 
-       if (n == 0 && sp->sou_size_in_bits != 0) {
+       if (!has_named_member && sp->sou_size_in_bits != 0) {
                /* '%s' has no named members */
                warning(65, type_name(tp));
        }