linux: Yet more malloc() avoidance for backtrace()

Turns out, there's an initializer at the top of backtrace() that (on
some arches) calls dlopen().  dlopen(), unsurprisingly, calls malloc().
So, call backtrace() early in signal handler setup so we can later
safely call it from the signal handler itself.

1 files changed, 14 insertions, 0 deletions

diff --git a/os/osinit.c b/os/osinit.c
index 17a2bedc7..e8fcd4540 100644
--- a/os/osinit.c
+++ b/os/osinit.c
@@ -59,6 +59,10 @@ SOFTWARE.
 #ifdef HAVE_DLFCN_H
 # include <dlfcn.h>
 #endif
+#ifdef HAVE_BACKTRACE
+#include <execinfo.h>
+#endif
+
 
 #include "dixstruct.h"
 
@@ -192,6 +196,16 @@ OsInit(void)
 		       siglist[i], strerror(errno));
 	    }
 	}
+#ifdef HAVE_BACKTRACE
+	/*
+	 * initialize the backtracer, since the ctor calls dlopen(), which
+	 * calls malloc(), which isn't signal-safe.
+	 */
+	do {
+	    void *array;
+	    backtrace(&array, 1);
+	} while (0);
+#endif
 
 #ifdef RTLD_DI_SETSIGNAL
 	/* Tell runtime linker to send a signal we can catch instead of SIGKILL