work around "signal loses thread pointer" issue with "approach 2"

this was discussed on the mailing list and no consensus on the
preferred solution was reached, so in anticipation of a release, i'm
just committing a minimally-invasive solution that avoids the problem
by ensuring that multi-threaded-capable programs will always have
initialized the thread pointer before any signal handler can run.

in the long term we may switch to initializing the thread pointer at
program start time whenever the program has the potential to access
any per-thread data.

1 files changed, 5 insertions, 0 deletions

diff --git a/src/signal/sigaction.c b/src/signal/sigaction.c
index 18956c6b..5bc9383b 100644
--- a/src/signal/sigaction.c
+++ b/src/signal/sigaction.c
@@ -3,9 +3,13 @@
 #include <errno.h>
 #include "syscall.h"
 #include "pthread_impl.h"
+#include "libc.h"
 
 void __restore(), __restore_rt();
 
+static pthread_t dummy(void) { return 0; }
+weak_alias(dummy, __pthread_self_def);
+
 int __libc_sigaction(int sig, const struct sigaction *sa, struct sigaction *old)
 {
 	struct {
@@ -23,6 +27,7 @@ int __libc_sigaction(int sig, const struct sigaction *sa, struct sigaction *old)
 		pksa = (long)&ksa;
 	}
 	if (old) pkold = (long)&kold;
+	__pthread_self_def();
 	if (syscall(SYS_rt_sigaction, sig, pksa, pkold, 8))
 		return -1;
 	if (old) {