[PATCH v4] gcov: Runtime configurable destination output

[Aaron Conole <aconole@bytheb.org>]

The previous gcov behavior was to always output errors on the stderr channel.
This is fine for most uses, but some programs will require stderr to be
untouched by libgcov for certain tests. This change allows configuring
the gcov output via an environment variable which will be used to open
the appropriate file.
---
 libgcc/libgcov-driver-system.c | 49 ++++++++++++++++++++++++++++++++++++++++--
 libgcc/libgcov-driver.c        |  8 ++++++-
 2 files changed, 54 insertions(+), 3 deletions(-)

diff --git a/libgcc/libgcov-driver-system.c b/libgcc/libgcov-driver-system.c
index 4e3b244..ff8a521 100644
--- a/libgcc/libgcov-driver-system.c
+++ b/libgcc/libgcov-driver-system.c
@@ -23,19 +23,64 @@ a copy of the GCC Runtime Library Exception along with this program;
 see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 <http://www.gnu.org/licenses/>.  */
 
-/* A utility function for outputing errors.  */
+/* Configured via the GCOV_ERROR_FILE environment variable;
+   it will either be stderr, or a file of the user's choosing.
+   Non-static to prevent multiple gcov-aware shared objects from
+   instantiating their own copies. */
+FILE *__gcov_error_file = NULL;
+
+/* A utility function to populate the __gcov_error_file pointer.
+   This should NOT be called outside of the gcov system driver code. */
+
+static FILE *
+get_gcov_error_file(void)
+{
+#if !IN_GCOV_TOOL
+  return stderr;
+#else
+  char *gcov_error_filename = getenv ("GCOV_ERROR_FILE");
+
+  if (gcov_error_filename)
+    {
+      FILE *openfile = fopen (gcov_error_filename, "a");
+      if (openfile)
+        __gcov_error_file = openfile;
+    }
+  if (!__gcov_error_file)
+    __gcov_error_file = stderr;
+  return __gcov_error_file;
+#endif
+}
+
+/* A utility function for outputting errors.  */
 
 static int __attribute__((format(printf, 1, 2)))
 gcov_error (const char *fmt, ...)
 {
   int ret;
   va_list argp;
+
+  if (!__gcov_error_file)
+    __gcov_error_file = get_gcov_error_file ();
+
   va_start (argp, fmt);
-  ret = vfprintf (stderr, fmt, argp);
+  ret = vfprintf (__gcov_error_file, fmt, argp);
   va_end (argp);
   return ret;
 }
 
+#if !IN_GCOV_TOOL
+static void
+gcov_error_exit (void)
+{
+  if (__gcov_error_file && __gcov_error_file != stderr)
+    {
+      fclose (__gcov_error_file);
+      __gcov_error_file = NULL;
+    }
+}
+#endif
+
 /* Make sure path component of the given FILENAME exists, create
    missing directories. FILENAME must be writable.
    Returns zero on success, or -1 if an error occurred.  */
diff --git a/libgcc/libgcov-driver.c b/libgcc/libgcov-driver.c
index 9c4eeca..d51397e 100644
--- a/libgcc/libgcov-driver.c
+++ b/libgcc/libgcov-driver.c
@@ -43,9 +43,13 @@ void __gcov_init (struct gcov_info *p __attribute__ ((unused))) {}
 
 #ifdef L_gcov
 
-/* A utility function for outputing errors.  */
+/* A utility function for outputting errors.  */
 static int gcov_error (const char *, ...);
 
+#if !IN_GCOV_TOOL
+static void gcov_error_exit (void);
+#endif
+
 #include "gcov-io.c"
 
 struct gcov_fn_buffer
@@ -878,6 +882,8 @@ gcov_exit (void)
     __gcov_root.prev->next = __gcov_root.next;
   else
     __gcov_master.root = __gcov_root.next;
+
+  gcov_error_exit ();
 }
 
 /* Add a new object file onto the bb chain.  Invoked automatically
-- 
2.5.5