From 584c6304cf0036928b494ea7916f9b41a5d3e3b6 Mon Sep 17 00:00:00 2001 From: Yunzhong Gao Date: Thu, 13 Feb 2014 02:45:10 +0000 Subject: [PATCH] Fixing a compiler assertion with zero-width bit-fields in packed structs. According to the GNU docs, zero-sized bitfields should not be affected by the packed attribute. Differential Revision: http://llvm-reviews.chandlerc.com/D2693 git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@201288 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/AST/RecordLayoutBuilder.cpp | 4 ++-- test/Sema/bitfield-layout.c | 15 +++++++++++++++ 2 files changed, 17 insertions(+), 2 deletions(-) diff --git a/lib/AST/RecordLayoutBuilder.cpp b/lib/AST/RecordLayoutBuilder.cpp index cffdcaf743..139ee60ef8 100644 --- a/lib/AST/RecordLayoutBuilder.cpp +++ b/lib/AST/RecordLayoutBuilder.cpp @@ -1552,8 +1552,8 @@ void RecordLayoutBuilder::LayoutBitField(const FieldDecl *D) { // Remember the alignment we would have used if the field were not packed. unsigned UnpackedFieldAlign = FieldAlign; - // Ignore the field alignment if the field is packed. - if (!IsMsStruct && FieldPacked) + // Ignore the field alignment if the field is packed unless it has zero-size. + if (!IsMsStruct && FieldPacked && FieldSize != 0) FieldAlign = 1; // But, if there's an 'aligned' attribute on the field, honor that. diff --git a/test/Sema/bitfield-layout.c b/test/Sema/bitfield-layout.c index d226391475..2abd139d23 100644 --- a/test/Sema/bitfield-layout.c +++ b/test/Sema/bitfield-layout.c @@ -9,6 +9,21 @@ struct a {char x; int : 0; char y;}; CHECK_SIZE(struct, a, 5) CHECK_ALIGN(struct, a, 1) +// Zero-width bit-fields with packed +struct __attribute__((packed)) a2 { short x : 9; char : 0; int y : 17; }; +CHECK_SIZE(struct, a2, 5) +CHECK_ALIGN(struct, a2, 1) + +// Zero-width bit-fields at the end of packed struct +struct __attribute__((packed)) a3 { short x : 9; int : 0; }; +CHECK_SIZE(struct, a3, 4) +CHECK_ALIGN(struct, a3, 1) + +// For comparison, non-zero-width bit-fields at the end of packed struct +struct __attribute__((packed)) a4 { short x : 9; int : 1; }; +CHECK_SIZE(struct, a4, 2) +CHECK_ALIGN(struct, a4, 1) + union b {char x; int : 0; char y;}; CHECK_SIZE(union, b, 1) CHECK_ALIGN(union, b, 1) -- 2.40.0