False positive valgrind error: uninitialized sigset_t.

The issue is that sigset_t is 1024 bits wide on Linux, but
there aren't actually that many signals. Valgrind knows this
and so when sigprocmask returns the old signal set, Valgrind
only marks a portion of it as initialized, and not the
entire 1024 bits. When this sigset_t is later passed into
sig_set again, we do a memcmp on all 1024 bits and Valgrind
complains about a use of uninitialized data. Test case:
run valgrind ./txr -i and execute a (throw 'foo) expr.

* signal.c (sig_mask): If we are compiling with Valgrind
support, mark the old signal set defined just before passing
it to sigprocmask, so it has no uninitialized bits.

1 files changed, 6 insertions, 0 deletions

diff --git a/signal.c b/signal.c
index b5f8f464..05554a64 100644
--- a/signal.c
+++ b/signal.c
@@ -37,6 +37,9 @@
 #if HAVE_SYS_TIME
 #include <sys/time.h>
 #endif
+#if HAVE_VALGRIND
+#include <valgrind/memcheck.h>
+#endif
 #include "lib.h"
 #include "gc.h"
 #include "signal.h"
@@ -366,6 +369,9 @@ int sig_mask(int how, const sigset_t *set, sigset_t *oldset)
 
   if (memcmp(&sig_blocked_cache, pnew, sizeof *pnew) != 0) {
     sig_blocked_cache = *pnew;
+#if HAVE_VALGRIND
+    VALGRIND_MAKE_MEM_DEFINED(oldset, sizeof *oldset);
+#endif
     return sigprocmask(SIG_SETMASK, &sig_blocked_cache, oldset);
   }