linux, compat: add a memfd_create wrapper

Change-Id: Iecbf85d0e963779b4c16083b481f4ab50f509115
Reviewed-on: https://chromium-review.googlesource.com/c/crashpad/crashpad/+/1774899
Commit-Queue: Joshua Peraza <jperaza@chromium.org>
Reviewed-by: Mark Mentovai <mark@chromium.org>

compat/BUILD.gn

@@ -79,6 +79,8 @@ compat_target("compat") {
   if (crashpad_is_linux || crashpad_is_android) {
     sources += [
       "linux/signal.h",
+      "linux/sys/mman.cc",
+      "linux/sys/mman.h",
       "linux/sys/ptrace.h",
       "linux/sys/user.h",
     ]

compat/linux/sys/mman.cc

@@ -0,0 +1,35 @@
+// Copyright 2019 The Crashpad Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <sys/mman.h>
+
+#include <dlfcn.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+#if defined(__GLIBC__)
+
+extern "C" {
+
+int memfd_create(const char* name, unsigned int flags) {
+  using MemfdCreateType = int (*)(const char*, int);
+  static const MemfdCreateType next_memfd_create =
+      reinterpret_cast<MemfdCreateType>(dlsym(RTLD_NEXT, "memfd_create"));
+  return next_memfd_create ? next_memfd_create(name, flags)
+                           : syscall(SYS_memfd_create, name, flags);
+}
+
+}  // extern "C"
+
+#endif  // __GLIBC__

compat/linux/sys/mman.h

@@ -0,0 +1,40 @@
+// Copyright 2019 The Crashpad Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef CRASHPAD_COMPAT_LINUX_SYS_MMAN_H_
+#define CRASHPAD_COMPAT_LINUX_SYS_MMAN_H_
+
+#include_next <sys/mman.h>
+
+#include <features.h>
+
+// There's no memfd_create() wrapper before glibc 2.27.
+// This can't select for glibc < 2.27 because linux-chromeos-rel bots build this
+// code using a sysroot which has glibc 2.27, but then run it on Ubuntu 16.04,
+// which doesn't.
+#if defined(__GLIBC__)
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+int memfd_create(const char* name, unsigned int flags);
+
+#ifdef __cplusplus
+}  // extern "C"
+#endif
+
+#endif  // __GLIBC__
+
+#endif  // CRASHPAD_COMPAT_LINUX_SYS_MMAN_H_