Wrap getenv and append euid to GCOV_PREFIX

The coverage runtime creates coverage files with permissions 0644 and
intermediate directories with 0755.  This causes conflicts and
permissions issues when multiple processes create/access the same file
or directory under $GCOV_PREFIX.  Some processes also call umask, which
further complicates things.

It is possible to handle all of these in the coverage runtime library
but a foolproof alternative is to have a separate coverage directory per
effective userid (euid) by customizing GCOV_PREFIX.

This change adds a wrapper to getenv which appends the euid of the
current process for the "GCOV_PREFIX" environment variable.

Bug: 148178774
Test: Verify that coverage files are written to
/data/misc/trace/<euid>/proc/... instead of /data/misc/trace/proc/...

Change-Id: I6be1e748618d84697c354516ab1c734fb33ab5f4
Merged-In: I6be1e748618d84697c354516ab1c734fb33ab5f4
(cherry picked from commit a277ce976288ac0a35a9016970f6e49037eaeadb)

2 files changed, 47 insertions, 0 deletions

diff --git a/toolchain-extras/Android.bp b/toolchain-extras/Android.bp
index 727f9795..5c839a1e 100644
--- a/toolchain-extras/Android.bp
+++ b/toolchain-extras/Android.bp
@@ -2,6 +2,7 @@ cc_defaults {
     name: "libprofile-defaults",
     srcs: [
         "profile-extras.cpp",
+        "profile-globals.c",
     ],
     native_coverage: false,
 }
@@ -24,6 +25,10 @@ cc_library_static {
 cc_library_static {
     name: "libprofile-extras_ndk",
     defaults: ["libprofile-defaults",],
+    vendor_available: true,
+    vndk: {
+        enabled: true,
+    },
 
     sdk_version: "minimum",
 }
diff --git a/toolchain-extras/profile-globals.c b/toolchain-extras/profile-globals.c
new file mode 100644
index 00000000..95bd46dd
--- /dev/null
+++ b/toolchain-extras/profile-globals.c
@@ -0,0 +1,42 @@
+/*
+ * Copyright (C) 2019 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 <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/types.h>
+
+// This file provides a wrapper for getenv that appends the userid (geteuid())
+// of the current process to GCOV_PREFIX.  This avoids conflicts and permissions
+// issues when different processes try to create/access the same directories and
+// files under $GCOV_PREFIX.
+//
+// When this file is linked to a binary, the -Wl,--wrap,getenv flag must be
+// used.  The linker redirects calls to getenv to __wrap_getenv and sets
+// __real_getenv to point to libc's getenv.
+
+char *__real_getenv(const char *name);
+
+static char modified_gcov_prefix[128];
+
+__attribute__((weak)) char *__wrap_getenv(const char *name) {
+  if (strcmp(name, "GCOV_PREFIX") != 0) {
+    return __real_getenv(name);
+  }
+
+  sprintf(modified_gcov_prefix, "%s/%u", __real_getenv(name), geteuid());
+  return modified_gcov_prefix;
+}