[profile] In Android, do not mkdir() dirs in GCOV_PREFIX

[pirama]

Summary

In Android, attempting to mkdir() or even stat() top-level directories
like /data causes noisy selinux denials. During whole-system coverage
instrumentation, this causes a deluge of noisy messages that drown out
legitimate selinux denials, that should be audited and fixed.

To avoid this, skip creating any directory in GCOV_PREFIX (thereby
assuming that it exists).

• Android platform ensures that the GCOV_PREFIX used in Android is

created and read/writable by all processes.

• This only affects the Android platform (by checking against

ANDROID_API_FUTURE) and for apps built with Clang coverage, the
runtime will still create any non-existent parent directories for the
coverage files.

[davidxl]

compiler-rt/lib/profile/InstrProfilingUtil.c

53 ↗

(On Diff #211608)

getenv is repeatedly called in the loop which is not desired. Can you add a helper function and call it outside the loop to 'strip' the prefix from path?

[pirama]

Refactored the loop to call getenv just once.

[pirama]

Remove stray new line.

[pirama]

compiler-rt/lib/profile/InstrProfilingUtil.c

53 ↗

(On Diff #211608)

I refactored to call getenv() just once. I kept the special case within this function to avoiding adding #ifdef ANDROID at two different places, but happy to add if you think that'd make this function cleaner.

[davidxl]

compiler-rt/lib/profile/InstrProfilingUtil.c

52 ↗

(On Diff #211819)

needs null check of gcov_prefix.

[pirama]

Call strlen(gcov_prefix) only if its not null.

[pirama]

compiler-rt/lib/profile/InstrProfilingUtil.c

52 ↗

(On Diff #211819)

Aah, good catch. Sorry I missed this.

[davidxl]

lgtm

[pirama]

Apply clang-format

compiler-rt/trunk/lib/profile/InstrProfilingUtil.c

 #include "InstrProfiling.h"
 #include "InstrProfilingUtil.h"
 
 COMPILER_RT_WEAK unsigned lprofDirMode = 0755;
 
 COMPILER_RT_VISIBILITY
 void __llvm_profile_recursive_mkdir(char *path) {
   int i;
+  int start = 1;
 
-  for (i = 1; path[i] != '\0'; ++i) {
+#if defined(__ANDROID__) && defined(__ANDROID_API__) &&                        \
+    defined(__ANDROID_API_FUTURE__) &&                                         \
+    __ANDROID_API__ == __ANDROID_API_FUTURE__
+  // Avoid spammy selinux denial messages in Android by not attempting to
+  // create directories in GCOV_PREFIX.  These denials occur when creating (or
+  // even attempting to stat()) top-level directories like "/data".
+  //
+  // Do so by ignoring ${GCOV_PREFIX} when invoking mkdir().
+  const char *gcov_prefix = getenv("GCOV_PREFIX");
+  if (gcov_prefix != NULL) {
+    const int gcov_prefix_len = strlen(gcov_prefix);
+    if (strncmp(path, gcov_prefix, gcov_prefix_len) == 0)
+      start = gcov_prefix_len;
+  }
+#endif
+
+  for (i = start; path[i] != '\0'; ++i) {
     char save = path[i];
     if (!IS_DIR_SEPARATOR(path[i]))
       continue;
     path[i] = '\0';
 #ifdef _WIN32
     _mkdir(path);
 #else
     /* Some of these will fail, ignore it. */