android: Add libwrap.c for inspecting on android

This lets us see what native calls android apps make.

1 files changed, 95 insertions, 0 deletions

diff --git a/android/libwrap.c b/android/libwrap.c
new file mode 100644
index 0000000..2a029d6
--- /dev/null
+++ b/android/libwrap.c
@@ -0,0 +1,95 @@
+// Need android-ndk, compile with:
+// i686-linux-android-gcc --sysroot=$ANDROID_NDK/platforms/android-9/arch-x86 -std=c99 -shared -I../src -DANDROID_X86_LINKER -DVERBOSE_FUNCTIONS libwrap.c ../src/wrapper/wrapper.c ../src/jvm/jvm.c -llog -o libwrap.so
+// Rename libwrap.so to the library's name you want to middle-man, and the original library to liborig.so
+//
+// We use logging thread to avoid putting android specific code to verbose/wrapper.h
+// Logging thread will catch stdout && stderr.
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <dlfcn.h>
+#include <pthread.h>
+#include <assert.h>
+#include <android/log.h>
+#include "jvm/jvm.h"
+#include "wrapper/wrapper.h"
+
+static int pfd[2];
+
+static void*
+log_thread(void *arg)
+{
+    char buf[255];
+    ssize_t r;
+    while ((r = read(pfd[0], buf, sizeof(buf) - 1)) > 0) {
+        r = (r > 0 && buf[r - 1] == '\n' ? r - 1 : r);
+        buf[r] = 0;
+        __android_log_write(ANDROID_LOG_INFO, "native", buf);
+    }
+    return NULL;
+}
+
+static void
+stdlog_workaround(void)
+{
+    setvbuf(stdout, 0, _IOLBF, 0);
+    setvbuf(stderr, 0, _IONBF, 0);
+    pipe(pfd);
+    dup2(pfd[1], 1);
+    dup2(pfd[1], 2);
+    pthread_t thread;
+    pthread_create(&thread, 0, log_thread, NULL);
+    pthread_detach(thread);
+}
+
+JNIEXPORT jint JNICALL
+JNI_OnLoad(JavaVM *vm, void *reserved)
+{
+    stdlog_workaround();
+
+    __android_log_print(ANDROID_LOG_INFO, "native", "Loading liborig.so");
+    void *handle = dlopen("liborig.so", RTLD_NOW);
+    assert(handle);
+
+    jint (*JNI_OnLoad)(JavaVM*, void*) = dlsym(handle, "JNI_OnLoad");
+    assert(JNI_OnLoad);
+
+    struct jvm jvm;
+    jvm_init(&jvm);
+
+    __android_log_print(ANDROID_LOG_INFO, "native", "Call liborig's JNI_OnLoad with fakevm");
+    JNI_OnLoad(&jvm.vm, NULL);
+
+    // Sort of hack, may fail on some libraries maybe.
+    // Some libs store the vm ^ in above call, we want it to use the real vm though.
+    // We only pass fake vm in above call to know what natives it registered.
+    JNI_OnLoad(vm, NULL);
+
+    JNIEnv *env;
+    if ((*vm)->GetEnv(vm, (void**)&env, JNI_VERSION_1_6) != JNI_OK)
+       return -1;
+
+    __android_log_print(ANDROID_LOG_INFO, "native", "Wrapping natives methods");
+
+    jclass old_klass = jvm.methods[0].method.klass;
+    JNINativeMethod methods[255];
+    for (size_t i = 0, c = 0; c < 255 && i < 255; ++i, ++c) {
+        if (jvm.methods[i].method.klass != old_klass) {
+            assert(old_klass > 0);
+            jclass klass = (*env)->FindClass(env, jvm.objects[(intptr_t)old_klass - 1].klass.name.data);
+            (*env)->RegisterNatives(env, klass, methods, c);
+            old_klass = jvm.methods[i].method.klass;
+            c = 0;
+        }
+
+        if (!jvm.methods[i].function)
+            break;
+
+        methods[c].name = jvm.methods[i].method.name.data;
+        methods[c].signature = jvm.methods[i].method.signature.data;
+        methods[c].fnPtr = wrapper_create(methods[c].name, jvm.methods[i].function);
+    }
+
+    return JNI_VERSION_1_6;
+}