[Qemu-devel] [PATCH 1/2] coroutine-ucontext: Help valgrind understand coroutines

[Kevin Wolf <kwolf@redhat.com>]

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>
---
 configure            |   18 ++++++++++++++++++
 coroutine-ucontext.c |   21 +++++++++++++++++++++
 2 files changed, 39 insertions(+), 0 deletions(-)

diff --git a/configure b/configure
index 500fe24..b424fcf 100755
--- a/configure
+++ b/configure
@@ -2855,6 +2855,20 @@ if compile_prog "" "" ; then
 fi
 
 ########################################
+# check if we have valgrind/valgrind.h
+
+valgrind_h=no
+cat > $TMPC << EOF
+#include <valgrind/valgrind.h>
+int main(void) {
+  return 0;
+}
+EOF
+if compile_prog "" "" ; then
+    valgrind_h=yes
+fi
+
+########################################
 # check if environ is declared
 
 has_environ=no
@@ -3380,6 +3394,10 @@ 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
diff --git a/coroutine-ucontext.c b/coroutine-ucontext.c
index 5f43083..db4ba88 100644
--- a/coroutine-ucontext.c
+++ b/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
+    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,
@@ -196,6 +210,13 @@ void qemu_coroutine_delete(Coroutine *co_)
         return;
     }
 
+#ifdef CONFIG_VALGRIND_H
+    /* Work around an unused variable in the valgrind.h macro... */
+    #pragma GCC diagnostic push
+    #pragma GCC diagnostic ignored "-Wunused-but-set-variable"
+    VALGRIND_STACK_DEREGISTER(co->valgrind_stack_id);
+    #pragma GCC diagnostic pop
+#endif
     g_free(co->stack);
     g_free(co);
 }
-- 
1.7.6.5