Add a "smash-stack" option to crasher.

bionic's __stack_chk_fail was preventing debuggerd from dumping
stacks, which was not helpful.

Bug: 2487269
Change-Id: Idba2a274037b960dfb2ac1c21686323268c4b372

2 files changed, 14 insertions, 0 deletions

diff --git a/debuggerd/Android.mk b/debuggerd/Android.mk
index e48b9af..3fca64f 100644
--- a/debuggerd/Android.mk
+++ b/debuggerd/Android.mk
@@ -37,6 +37,7 @@ LOCAL_SRC_FILES += $(TARGET_ARCH)/crashglue.S
 LOCAL_MODULE := crasher
 LOCAL_MODULE_PATH := $(TARGET_OUT_OPTIONAL_EXECUTABLES)
 LOCAL_MODULE_TAGS := optional
+LOCAL_CFLAGS += -fstack-protector-all
 #LOCAL_FORCE_STATIC_EXECUTABLE := true
 LOCAL_SHARED_LIBRARIES := libcutils libc
 include $(BUILD_EXECUTABLE)
diff --git a/debuggerd/crasher.c b/debuggerd/crasher.c
index 74eaa49..134fe80 100644
--- a/debuggerd/crasher.c
+++ b/debuggerd/crasher.c
@@ -35,6 +35,18 @@ static void debuggerd_connect()
     }
 }
 
+int smash_stack(int i) {
+    printf("crasher: deliberately corrupting stack...\n");
+    // Unless there's a "big enough" buffer on the stack, gcc
+    // doesn't bother inserting checks.
+    char buf[8];
+    // If we don't write something relatively unpredicatable
+    // into the buffer and then do something with it, gcc
+    // optimizes everything away and just returns a constant.
+    *(int*)(&buf[7]) = (uintptr_t) &buf[0];
+    return *(int*)(&buf[0]);
+}
+
 void test_call1()
 {
     *((int*) 32) = 1;
@@ -95,6 +107,7 @@ int do_action(const char* arg)
         return do_action_on_thread(arg + strlen("thread-"));
     }
 
+    if(!strcmp(arg,"smash-stack")) return smash_stack(42);
     if(!strcmp(arg,"nostack")) crashnostack();
     if(!strcmp(arg,"ctest")) return ctest();
     if(!strcmp(arg,"exit")) exit(1);