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From 6b633c4b14850df376d5cec571699018772f358e Mon Sep 17 00:00:00 2001
From: Tomas Popela <tomas.popela@gmail.com>
Date: Tue, 17 Sep 2019 19:48:48 +0000
Subject: [PATCH] GCC: Can't use alignas() together with __attribute__()
It's because GCC has problems when mixing the alignas() together with
__attribute__() (that is used to export the symbols). The best
solution is to use ALIGNAS() macro from //base/compiler_specific.h
together with alignof() to have the equal functionality that compiles on
GCC as well as on clang.
Bug: 819294
Change-Id: Ieb169592a2965f17a18bfc88d28418eb723a4e5a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1806735
Auto-Submit: Tom Popela <tomas.popela@gmail.com>
Commit-Queue: Alex Clarke <alexclarke@chromium.org>
Reviewed-by: Alex Clarke <alexclarke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#697330}
---
diff --git a/base/task/promise/dependent_list.h b/base/task/promise/dependent_list.h
index 020bdbfc..3245c1c 100644
--- a/base/task/promise/dependent_list.h
+++ b/base/task/promise/dependent_list.h
@@ -59,7 +59,7 @@
// Align Node on an 8-byte boundary to ensure the first 3 bits are 0 and can
// be used to store additional state (see static_asserts below).
- class BASE_EXPORT alignas(8) Node {
+ class BASE_EXPORT ALIGNAS(8) Node {
public:
Node();
explicit Node(Node&& other) noexcept;
Re-use chromium alignas workaround in protobuf.
---
diff --git a/third_party/protobuf/src/google/protobuf/port_def.inc b/third_party/protobuf/src/google/protobuf/port_def.inc
index f1bd85d..9c204a1 100644
--- a/third_party/protobuf/src/google/protobuf/port_def.inc
+++ b/third_party/protobuf/src/google/protobuf/port_def.inc
@@ -528,6 +528,35 @@ PROTOBUF_EXPORT_TEMPLATE_TEST(DEFAULT, __declspec(dllimport));
#undef IN
#endif // _MSC_VER
+// Specify memory alignment for structs, classes, etc.
+// Use like:
+// class PROTOBUF_ALIGNAS(16) MyClass { ... }
+// PROTOBUF_ALIGNAS(16) int array[4];
+//
+// In most places you can use the C++11 keyword "alignas", which is preferred.
+//
+// But compilers have trouble mixing __attribute__((...)) syntax with
+// alignas(...) syntax.
+//
+// Doesn't work in clang or gcc:
+// struct alignas(16) __attribute__((packed)) S { char c; };
+// Works in clang but not gcc:
+// struct __attribute__((packed)) alignas(16) S2 { char c; };
+// Works in clang and gcc:
+// struct alignas(16) S3 { char c; } __attribute__((packed));
+//
+// There are also some attributes that must be specified *before* a class
+// definition: visibility (used for exporting functions/classes) is one of
+// these attributes. This means that it is not possible to use alignas() with a
+// class that is marked as exported.
+#if defined(_MSC_VER)
+#define PROTOBUF_ALIGNAS(byte_alignment) __declspec(align(byte_alignment))
+#elif defined(__GNUC__)
+#define PROTOBUF_ALIGNAS(byte_alignment) __attribute__((aligned(byte_alignment)))
+#else
+#define PROTOBUF_ALIGNAS(byte_alignment) alignas(byte_alignment)
+#endif
+
#if defined(__clang__)
#pragma clang diagnostic push
// TODO(gerbens) ideally we cleanup the code. But a cursory try shows many
diff --git a/third_party/protobuf/src/google/protobuf/arena.h b/third_party/protobuf/src/google/protobuf/arena.h
index dedc221..a8515ce 100644
--- a/third_party/protobuf/src/google/protobuf/arena.h
+++ b/third_party/protobuf/src/google/protobuf/arena.h
@@ -245,7 +245,7 @@ struct ArenaOptions {
// well as protobuf container types like RepeatedPtrField and Map. The protocol
// is internal to protobuf and is not guaranteed to be stable. Non-proto types
// should not rely on this protocol.
-class PROTOBUF_EXPORT alignas(8) Arena final {
+class PROTOBUF_EXPORT PROTOBUF_ALIGNAS(8) Arena final {
public:
// Arena constructor taking custom options. See ArenaOptions below for
// descriptions of the options available.
diff --git a/third_party/protobuf/src/google/protobuf/port_def.inc b/third_party/protobuf/src/google/protobuf/port_def.inc
index f1bd85d..6d02b53 100644
--- a/third_party/protobuf/src/google/protobuf/port_def.inc
+++ b/third_party/protobuf/src/google/protobuf/port_def.inc
@@ -528,6 +528,35 @@ PROTOBUF_EXPORT_TEMPLATE_TEST(DEFAULT, __declspec(dllimport));
#undef IN
#endif // _MSC_VER
+// Specify memory alignment for structs, classes, etc.
+// Use like:
+// class PROTOBUF_ALIGNAS(16) MyClass { ... }
+// PROTOBUF_ALIGNAS(16) int array[4];
+//
+// In most places you can use the C++11 keyword "alignas", which is preferred.
+//
+// But compilers have trouble mixing __attribute__((...)) syntax with
+// alignas(...) syntax.
+//
+// Doesn't work in clang or gcc:
+// struct alignas(16) __attribute__((packed)) S { char c; };
+// Works in clang but not gcc:
+// struct __attribute__((packed)) alignas(16) S2 { char c; };
+// Works in clang and gcc:
+// struct alignas(16) S3 { char c; } __attribute__((packed));
+//
+// There are also some attributes that must be specified *before* a class
+// definition: visibility (used for exporting functions/classes) is one of
+// these attributes. This means that it is not possible to use alignas() with a
+// class that is marked as exported.
+#if defined(_MSC_VER)
+#define PROTOBUF_ALIGNAS(byte_alignment) __declspec(align(byte_alignment))
+#elif defined(__GNUC__)
+#define PROTOBUF_ALIGNAS(byte_alignment) __attribute__((aligned(byte_alignment)))
+#else
+#define PROTOBUF_ALIGNAS(byte_alignment) alignas(byte_alignment)
+#endif
+
#if defined(__clang__)
#pragma clang diagnostic push
// TODO(gerbens) ideally we cleanup the code. But a cursory try shows many
diff --git a/third_party/protobuf/src/google/protobuf/port_undef.inc b/third_party/protobuf/src/google/protobuf/port_undef.inc
index b7e67fe..ba1fffc 100644
--- a/third_party/protobuf/src/google/protobuf/port_undef.inc
+++ b/third_party/protobuf/src/google/protobuf/port_undef.inc
@@ -80,6 +80,7 @@
#undef PROTOBUF_EXPORT_TEMPLATE_STYLE_MATCH_foj3FJo5StF0OvIzl7oMxA__declspec
#undef PROTOBUF_EXPORT_TEMPLATE_STYLE_MATCH_DECLSPEC_dllexport
#undef PROTOBUF_EXPORT_TEMPLATE_STYLE_MATCH_DECLSPEC_dllimport
+#undef PROTOBUF_ALIGNAS
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