Move 32 bit/64 bit check into debuggerd.

On 64 bit systems, calls to dump_backtrace_to_file or dump_tombstone
try and directly contact the correct debuggerd (32 bit vs 64 bit)
by reading the elf information for the executable.
Unfortunately, system_server makes a call to dump_backtrace_to_file
and it doesn't have permissions to read the executable data, so it
defaults to always contacting the 64 bit debuggerd.
This CL changes the code so that all dump requests go to the 64 bit
debuggerd, which reads the elf information and redirects requests for
32 bit processes to the 32 bit debuggerd.

Testing:

- Forced the watchdog code in system_server to dump stacks and
  verified that all native stacks are dumped correctly.
- Verified that dumpstate and bugreport still properly dump the native
  processes on a 64 bit and 32 bit system.
- Intentionally forced the 64 bit to 32 bit redirect to write only a
  byte at a time and verified there are no errors, and no dropped data.
- Used debuggerd and debuggerd64 to dump 32 bit and 64 bit processes
  seemlessly.
- Used debuggerd on a 32 bit system to dump native stacks.

Bug: https://code.google.com/p/android/issues/detail?id=97024
Change-Id: Ie01945153bdc1c4ded696c7334b61d58575314d1

1 files changed, 13 insertions, 27 deletions

diff --git a/include/cutils/debugger.h b/include/cutils/debugger.h
index bae687d..285e1af 100644
--- a/include/cutils/debugger.h
+++ b/include/cutils/debugger.h
@@ -17,20 +17,14 @@
 #ifndef __CUTILS_DEBUGGER_H
 #define __CUTILS_DEBUGGER_H
 
+#include <sys/cdefs.h>
 #include <sys/types.h>
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+__BEGIN_DECLS
 
-#define DEBUGGER32_SOCKET_NAME "android:debuggerd"
-#define DEBUGGER64_SOCKET_NAME "android:debuggerd64"
-
-#if defined(__LP64__)
-#define DEBUGGER_SOCKET_NAME DEBUGGER64_SOCKET_NAME
-#else
-#define DEBUGGER_SOCKET_NAME DEBUGGER32_SOCKET_NAME
-#endif
+#define DEBUGGER_SOCKET_NAME "android:debuggerd"
+#define DEBUGGER32_SOCKET_NAME "android:debuggerd32"
+#define DEBUGGER64_SOCKET_NAME DEBUGGER_SOCKET_NAME
 
 typedef enum {
     // dump a crash
@@ -41,23 +35,17 @@ typedef enum {
     DEBUGGER_ACTION_DUMP_BACKTRACE,
 } debugger_action_t;
 
-typedef struct {
-    debugger_action_t action;
+// Make sure that all values have a fixed size so that this structure
+// is the same for 32 bit and 64 bit processes.
+// NOTE: Any changes to this structure must also be reflected in
+//       bionic/linker/debugger.cpp.
+typedef struct __attribute__((packed)) {
+    int32_t action;
     pid_t tid;
-    uintptr_t abort_msg_address;
+    uint64_t abort_msg_address;
     int32_t original_si_code;
 } debugger_msg_t;
 
-#if defined(__LP64__)
-// For a 64 bit process to contact the 32 bit debuggerd.
-typedef struct {
-    debugger_action_t action;
-    pid_t tid;
-    uint32_t abort_msg_address;
-    int32_t original_si_code;
-} debugger32_msg_t;
-#endif
-
 /* Dumps a process backtrace, registers, and stack to a tombstone file (requires root).
  * Stores the tombstone path in the provided buffer.
  * Returns 0 on success, -1 on error.
@@ -84,8 +72,6 @@ int dump_backtrace_to_file(pid_t tid, int fd);
  */
 int dump_backtrace_to_file_timeout(pid_t tid, int fd, int timeout_secs);
 
-#ifdef __cplusplus
-}
-#endif
+__END_DECLS
 
 #endif /* __CUTILS_DEBUGGER_H */