[coverage] Wrap calls to open

Bug: http://b/173448692

The coverage runtime creates files with uga+rw permissions but an
earlier umask call can restrict these and cause problems with profile
merging ('%Nm' in LLVM_PROFILE_FILE).  This change adds a wrapper to
`open` which will set the permissions again using `fchmod` for files
opened under the /data/misc/trace directory.

Test: Manually validate permissions of files under /data/misc/trace.
Test: libprofile-clang-extras-test
Change-Id: Iee7fe07b4bfb362fe5146c962b54affaa55ef380

3 files changed, 91 insertions, 1 deletions

diff --git a/toolchain-extras/Android.bp b/toolchain-extras/Android.bp
index dec5d404..ff537a52 100644
--- a/toolchain-extras/Android.bp
+++ b/toolchain-extras/Android.bp
@@ -41,6 +41,7 @@ cc_defaults {
     name: "libprofile-clang-defaults",
     srcs: [
         "profile-clang-extras.cpp",
+        "profile-clang-openat.cpp",
     ],
     native_coverage: false,
 }
@@ -86,3 +87,18 @@ cc_test {
     ldflags: ["-uinit_profile_extras"],
     native_coverage: false,
 }
+
+cc_test {
+    name: "libprofile-clang-extras-test",
+    srcs: [
+        "profile-clang-extras-test.cpp",
+    ],
+    static_libs: [
+        "libprofile-clang-extras",
+    ],
+    ldflags: [
+        "-uinit_profile_extras",
+        "-Wl,--wrap,open",
+    ],
+    native_coverage: false,
+}
diff --git a/toolchain-extras/profile-clang-extras-test.cpp b/toolchain-extras/profile-clang-extras-test.cpp
index 2bb7bdbb..0c746478 100644
--- a/toolchain-extras/profile-clang-extras-test.cpp
+++ b/toolchain-extras/profile-clang-extras-test.cpp
@@ -14,7 +14,10 @@
  * limitations under the License.
  */
 
+#include <fcntl.h>
 #include <gtest/gtest.h>
+#include <sys/stat.h>
+
 #include "profile-extras.h"
 
 static int flush_count = 0;
@@ -30,7 +33,23 @@ TEST(profile_extras, smoke) {
   flush_count = 0;
 
   ASSERT_EQ(0, flush_count);
-  kill(getpid(), GCOV_FLUSH_SIGNAL);
+  kill(getpid(), COVERAGE_FLUSH_SIGNAL);
   sleep(2);
   ASSERT_EQ(1, flush_count);
 }
+
+static const char* OPEN_AT_TEST_FNAME = "/data/misc/trace/test.profraw";
+TEST(profile_extras, openat) {
+  mode_t old_umask = umask(0077);
+  unlink(OPEN_AT_TEST_FNAME);
+
+  int fd = open(OPEN_AT_TEST_FNAME, O_RDWR | O_CREAT, 0666);
+  ASSERT_NE(fd, -1);
+  close(fd);
+  umask(old_umask);
+
+  struct stat stat_buf;
+  ASSERT_EQ(stat(OPEN_AT_TEST_FNAME, &stat_buf), 0);
+  ASSERT_EQ(stat_buf.st_mode & 0777, 0666);
+  unlink(OPEN_AT_TEST_FNAME);
+}
diff --git a/toolchain-extras/profile-clang-openat.cpp b/toolchain-extras/profile-clang-openat.cpp
new file mode 100644
index 00000000..f2f43d14
--- /dev/null
+++ b/toolchain-extras/profile-clang-openat.cpp
@@ -0,0 +1,55 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * 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 <fcntl.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+// This file provides a wrapper for open.
+
+extern "C" {
+
+int __real_open(const char* pathname, int flags, ...);
+
+static bool needs_mode(int flags) {
+  return ((flags & O_CREAT) == O_CREAT) || ((flags & O_TMPFILE) == O_TMPFILE);
+}
+
+static const char* PROFRAW_START = "/data/misc/trace/";
+static bool is_coverage_trace(const char* pathname) {
+  if (strncmp(pathname, PROFRAW_START, strlen(PROFRAW_START)) == 0) return true;
+  return false;
+}
+
+__attribute__((weak)) int __wrap_open(const char* pathname, int flags, ...) {
+  if (!needs_mode(flags)) {
+    return __real_open(pathname, flags);
+  }
+
+  va_list args;
+  va_start(args, flags);
+  mode_t mode = static_cast<mode_t>(va_arg(args, int));
+  va_end(args);
+
+  int ret = __real_open(pathname, flags, mode);
+  if (is_coverage_trace(pathname)) fchmod(ret, mode);
+  return ret;
+}
+}