bionic: Add magic to abort message
This change adds a 128-bit magic value just before the abort message
(and its length). This allows Chrome OS crash collector (which cannot
reliably correlate a crash with its corresponding tombstone) to extract
the abort message from the core dump.
Bug: 62387553
Test: /data/nativetest{,64}/debuggerd_test/*
Test: /data/nativetest{,64}/bionic-unit-tests{,-static}/*
Change-Id: I69ff021d773b3a10081ab16ddf6f23233320fb02
diff --git a/libc/bionic/android_set_abort_message.cpp b/libc/bionic/android_set_abort_message.cpp
index 268c4f3..58f24cf 100644
--- a/libc/bionic/android_set_abort_message.cpp
+++ b/libc/bionic/android_set_abort_message.cpp
@@ -29,6 +29,8 @@
#include <android/set_abort_message.h>
#include <pthread.h>
+#include <stdint.h>
+#include <stddef.h>
#include <string.h>
#include <sys/mman.h>
@@ -41,9 +43,32 @@
size_t size;
char msg[0];
};
+static_assert(
+ offsetof(abort_msg_t, msg) == sizeof(size_t),
+ "The in-memory layout of abort_msg_t is not consistent with what libdebuggerd expects.");
+
+struct magic_abort_msg_t {
+ uint64_t magic1;
+ uint64_t magic2;
+ abort_msg_t msg;
+};
+static_assert(offsetof(magic_abort_msg_t, msg) == 2 * sizeof(uint64_t),
+ "The in-memory layout of magic_abort_msg_t is not consistent with what automated "
+ "tools expect.");
abort_msg_t** __abort_message_ptr; // Accessible to __libc_init_common.
+[[clang::optnone]]
+static void fill_abort_message_magic(magic_abort_msg_t* new_magic_abort_message) {
+ // 128-bit magic for the abort message. Chosen by fair dice roll.
+ // This function is intentionally deoptimized to avoid the magic to be present
+ // in the final binary. This causes clang to only use instructions where parts
+ // of the magic are encoded into immediate arguments for the instructions in
+ // all supported architectures.
+ new_magic_abort_message->magic1 = 0xb18e40886ac388f0ULL;
+ new_magic_abort_message->magic2 = 0xc6dfba755a1de0b5ULL;
+}
+
__BIONIC_WEAK_FOR_NATIVE_BRIDGE
void android_set_abort_message(const char* msg) {
ScopedPthreadMutexLocker locker(&g_abort_msg_lock);
@@ -59,14 +84,15 @@
return;
}
- size_t size = sizeof(abort_msg_t) + strlen(msg) + 1;
+ size_t size = sizeof(magic_abort_msg_t) + strlen(msg) + 1;
void* map = mmap(nullptr, size, PROT_READ | PROT_WRITE, MAP_ANON | MAP_PRIVATE, -1, 0);
if (map == MAP_FAILED) {
return;
}
- abort_msg_t* new_abort_message = reinterpret_cast<abort_msg_t*>(map);
- new_abort_message->size = size;
- strcpy(new_abort_message->msg, msg);
- *__abort_message_ptr = new_abort_message;
+ magic_abort_msg_t* new_magic_abort_message = reinterpret_cast<magic_abort_msg_t*>(map);
+ fill_abort_message_magic(new_magic_abort_message);
+ new_magic_abort_message->msg.size = size;
+ strcpy(new_magic_abort_message->msg.msg, msg);
+ *__abort_message_ptr = &new_magic_abort_message->msg;
}