[Qemu-devel] [PATCH v2 12/13] ucontext: annotate coroutine stack for ASAN

[Marc-André Lureau]

It helps ASAN to detect more leaks on coroutine stacks, as found in
the following patch.

A similar work would need to be done for sigaltstack & windows fibers
to have similar coverage. Since ucontext is prefered, I didn't bother
checking the other coroutine implementations for now.

Signed-off-by: Marc-André Lureau <address@hidden>
---
 include/qemu/compiler.h   |  4 ++++
 util/coroutine-ucontext.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 50 insertions(+)

diff --git a/include/qemu/compiler.h b/include/qemu/compiler.h
index 340e5fdc09..5fcc4f7ec7 100644
--- a/include/qemu/compiler.h
+++ b/include/qemu/compiler.h
@@ -111,4 +111,8 @@
 #define GCC_FMT_ATTR(n, m)
 #endif
 
+#ifndef __has_feature
+#define __has_feature(x) 0 /* compatibility with non-clang compilers */
+#endif
+
 #endif /* COMPILER_H */
diff --git a/util/coroutine-ucontext.c b/util/coroutine-ucontext.c
index 6621f3f692..e78eae8766 100644
--- a/util/coroutine-ucontext.c
+++ b/util/coroutine-ucontext.c
@@ -31,6 +31,11 @@
 #include <valgrind/valgrind.h>
 #endif
 
+#if defined(__SANITIZE_ADDRESS__) || __has_feature(address_sanitizer)
+#define CONFIG_ASAN 1
+#include <sanitizer/asan_interface.h>
+#endif
+
 typedef struct {
     Coroutine base;
     void *stack;
@@ -59,11 +64,37 @@ union cc_arg {
     int i[2];
 };
 
+static void finish_switch_fiber(void *fake_stack_save)
+{
+#ifdef CONFIG_ASAN
+    const void *bottom_old;
+    size_t size_old;
+
+    __sanitizer_finish_switch_fiber(fake_stack_save, &bottom_old, &size_old);
+
+    if (!leader.stack) {
+        leader.stack = (void *)bottom_old;
+        leader.stack_size = size_old;
+    }
+#endif
+}
+
+static void start_switch_fiber(void **fake_stack_save,
+                               const void *bottom, size_t size)
+{
+#ifdef CONFIG_ASAN
+    __sanitizer_start_switch_fiber(fake_stack_save, bottom, size);
+#endif
+}
+
 static void coroutine_trampoline(int i0, int i1)
 {
     union cc_arg arg;
     CoroutineUContext *self;
     Coroutine *co;
+    void *fake_stack_save = NULL;
+
+    finish_switch_fiber(NULL);
 
     arg.i[0] = i0;
     arg.i[1] = i1;
@@ -72,9 +103,13 @@ static void coroutine_trampoline(int i0, int i1)
 
     /* Initialize longjmp environment and switch back the caller */
     if (!sigsetjmp(self->env, 0)) {
+        start_switch_fiber(&fake_stack_save,
+                           leader.stack, leader.stack_size);
         siglongjmp(*(sigjmp_buf *)co->entry_arg, 1);
     }
 
+    finish_switch_fiber(fake_stack_save);
+
     while (true) {
         co->entry(co->entry_arg);
         qemu_coroutine_switch(co, co->caller, COROUTINE_TERMINATE);
@@ -87,6 +122,7 @@ Coroutine *qemu_coroutine_new(void)
     ucontext_t old_uc, uc;
     sigjmp_buf old_env;
     union cc_arg arg = {0};
+    void *fake_stack_save = NULL;
 
     /* The ucontext functions preserve signal masks which incurs a
      * system call overhead.  sigsetjmp(buf, 0)/siglongjmp() does not
@@ -122,8 +158,12 @@ Coroutine *qemu_coroutine_new(void)
 
     /* swapcontext() in, siglongjmp() back out */
     if (!sigsetjmp(old_env, 0)) {
+        start_switch_fiber(&fake_stack_save, co->stack, co->stack_size);
         swapcontext(&old_uc, &uc);
     }
+
+    finish_switch_fiber(fake_stack_save);
+
     return &co->base;
 }
 
@@ -169,13 +209,19 @@ qemu_coroutine_switch(Coroutine *from_, Coroutine *to_,
     CoroutineUContext *from = DO_UPCAST(CoroutineUContext, base, from_);
     CoroutineUContext *to = DO_UPCAST(CoroutineUContext, base, to_);
     int ret;
+    void *fake_stack_save = NULL;
 
     current = to_;
 
     ret = sigsetjmp(from->env, 0);
     if (ret == 0) {
+        start_switch_fiber(action == COROUTINE_TERMINATE ?
+                           NULL : &fake_stack_save, to->stack, to->stack_size);
         siglongjmp(to->env, action);
     }
+
+    finish_switch_fiber(fake_stack_save);
+
     return ret;
 }
 
-- 
2.15.1.355.g36791d7216