[PATCH 2/4] coroutine: Add check for SafeStack in sigalstack

[Daniele Buono <dbuono@linux.vnet.ibm.com>]

LLVM's SafeStack instrumentation cannot be used inside signal handlers
that make use of sigaltstack().
Since coroutine-sigaltstack relies on sigaltstack(), it is not
compatible with SafeStack. The resulting binary is incorrect, with
different coroutines sharing the same unsafe stack and producing
undefined behavior at runtime.
To avoid this, we add a check in coroutine-sigaltstack that throws a
preprocessor #error and interrupt the compilation if SafeStack is
enabled.

Signed-off-by: Daniele Buono <dbuono@linux.vnet.ibm.com>
---
 util/coroutine-sigaltstack.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/util/coroutine-sigaltstack.c b/util/coroutine-sigaltstack.c
index f6fc49a0e5..b7cdc959f8 100644
--- a/util/coroutine-sigaltstack.c
+++ b/util/coroutine-sigaltstack.c
@@ -30,6 +30,10 @@
 #include "qemu-common.h"
 #include "qemu/coroutine_int.h"
 
+#ifdef CONFIG_SAFESTACK
+#error "SafeStack does not work with sigaltstack's implementation"
+#endif
+
 typedef struct {
     Coroutine base;
     void *stack;
-- 
2.26.2