[PATCH 4/6] Warn when attempting to log in a signal unsafe manner from signal context

[Chase Douglas]

Also, print out the offending message format. This will hopefully help
developers track down unsafe logging.

Signed-off-by: Chase Douglas <chase.douglas at canonical.com>
---
 os/log.c |   15 +++++++++++++++
 1 files changed, 15 insertions(+), 0 deletions(-)

diff --git a/os/log.c b/os/log.c
index 840439a..88ab1d7 100644
--- a/os/log.c
+++ b/os/log.c
@@ -288,6 +288,21 @@ LogVWrite(int verb, const char *f, va_list args)
     int len = 0;
     static Bool newline = TRUE;
 
+    if (inSignalContext) {
+        static const char warning[] = "Warning: attempting to log data in a "
+                                      "signal unsafe manner while in signal "
+                                      "context. Please update to use "
+                                      "xf86InSignalContext() and/or "
+                                      "LogMessageVerbSigSafe(). The offending "
+                                      "log format message is:\n";
+
+        write(logFileFd, warning, sizeof(warning) - 1);
+
+        write(logFileFd, f, strlen_sigsafe(f));
+
+        return;
+    }
+
     if (newline) {
         sprintf(tmpBuffer, "[%10.3f] ", GetTimeInMillis() / 1000.0);
         len = strlen(tmpBuffer);
-- 
1.7.9.1