From 5d66d5907ac3e76d1e382b8a8e8afe653bd00f4c Mon Sep 17 00:00:00 2001

From: Stephan Hartmann <stha09@googlemail.com>

Date: Sun, 31 May 2020 13:59:15 +0000

Subject: [PATCH] Fix GCC build with PROTOBUF_USE_DLLS enabled

GCC does not allow mixing __attribute__(()) syntax and alignas()

syntax. Re-use approach from chromium base/compiler_specific.h

---

 .../protobuf/src/google/protobuf/arena.h      |  2 +-

 .../protobuf/src/google/protobuf/port_def.inc | 29 +++++++++++++++++++

 .../src/google/protobuf/port_undef.inc        |  1 +

 3 files changed, 31 insertions(+), 1 deletion(-)

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

-- 

2.26.2