coroutine-ucontext: Help valgrind understand coroutines

valgrind tends to get confused and report false positives when you
switch stacks and don't tell it about it.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>

configure

@@ -2870,6 +2870,22 @@ if compile_prog "" "" ; then
     linux_magic_h=yes
 fi
 
+########################################
+# check if we have valgrind/valgrind.h
+
+valgrind_h=no
+cat > $TMPC << EOF
+#include <valgrind/valgrind.h>
+#pragma GCC diagnostic ignored "-Wunused-but-set-variable"
+int main(void) {
+  VALGRIND_STACK_DEREGISTER(0);
+  return 0;
+}
+EOF
+if compile_prog "" "" ; then
+    valgrind_h=yes
+fi
+
 ########################################
 # check if environ is declared
 
@@ -3379,6 +3395,10 @@ if test "$linux_magic_h" = "yes" ; then
   echo "CONFIG_LINUX_MAGIC_H=y" >> $config_host_mak
 fi
 
+if test "$valgrind_h" = "yes" ; then
+  echo "CONFIG_VALGRIND_H=y" >> $config_host_mak
+fi
+
 if test "$has_environ" = "yes" ; then
   echo "CONFIG_HAS_ENVIRON=y" >> $config_host_mak
 fi

coroutine-ucontext.c

@@ -30,6 +30,10 @@
 #include "qemu-common.h"
 #include "qemu-coroutine-int.h"
 
+#ifdef CONFIG_VALGRIND_H
+#include <valgrind/valgrind.h>
+#endif
+
 enum {
     /* Maximum free pool size prevents holding too many freed coroutines */
     POOL_MAX_SIZE = 64,
@@ -43,6 +47,11 @@ typedef struct {
     Coroutine base;
     void *stack;
     jmp_buf env;
+
+#ifdef CONFIG_VALGRIND_H
+    unsigned int valgrind_stack_id;
+#endif
+
 } CoroutineUContext;
 
 /**
@@ -159,6 +168,11 @@ static Coroutine *coroutine_new(void)
     uc.uc_stack.ss_size = stack_size;
     uc.uc_stack.ss_flags = 0;
 
+#ifdef CONFIG_VALGRIND_H
+    co->valgrind_stack_id =
+        VALGRIND_STACK_REGISTER(co->stack, co->stack + stack_size);
+#endif
+
     arg.p = co;
 
     makecontext(&uc, (void (*)(void))coroutine_trampoline,
@@ -185,6 +199,16 @@ Coroutine *qemu_coroutine_new(void)
     return co;
 }
 
+#ifdef CONFIG_VALGRIND_H
+/* Work around an unused variable in the valgrind.h macro... */
+#pragma GCC diagnostic ignored "-Wunused-but-set-variable"
+static inline void valgrind_stack_deregister(CoroutineUContext *co)
+{
+    VALGRIND_STACK_DEREGISTER(co->valgrind_stack_id);
+}
+#pragma GCC diagnostic error "-Wunused-but-set-variable"
+#endif
+
 void qemu_coroutine_delete(Coroutine *co_)
 {
     CoroutineUContext *co = DO_UPCAST(CoroutineUContext, base, co_);
@@ -196,6 +220,10 @@ void qemu_coroutine_delete(Coroutine *co_)
         return;
     }
 
+#ifdef CONFIG_VALGRIND_H
+    valgrind_stack_deregister(co);
+#endif
+
     g_free(co->stack);
     g_free(co);
 }