refactoring, fixing and implementing

messy commits yay

2 files changed, 74 insertions, 0 deletions

diff --git a/src/wrapper/wrapper.c b/src/wrapper/wrapper.c
new file mode 100644
index 0000000..5ed0943
--- /dev/null
+++ b/src/wrapper/wrapper.c
@@ -0,0 +1,70 @@
+#include "wrapper.h"
+#include <stdio.h>
+#include <stdint.h>
+#include <stddef.h>
+#include <stdlib.h>
+#include <string.h>
+#include <dlfcn.h>
+#include <assert.h>
+#include <sys/mman.h>
+
+#ifdef ANDROID_X86_LINKER
+__asm__(
+    "wrapper_start: nop\n"
+    "wrapper_symbol: pushl $0xFAFBFCFD\n"
+    "wrapper_trace: movl $0xFAFBFCFD, %eax\ncall *%eax\npop %eax\n"
+    "wrapper_call: movl $0xFAFBFCFD, %eax\njmp *%eax\n"
+    "wrapper_end: nop\n"
+);
+#   define WRAPPER_TRACE
+#else
+#   warning "no wrapper asm for this platform, function tracing is not available"
+#endif
+
+#ifdef WRAPPER_TRACE
+extern char wrapper_start, wrapper_symbol, wrapper_trace, wrapper_call, wrapper_end;
+static char* (*__cxa_demangle)(const char *mangled_name, char *output_buffer, size_t *length, int *status);
+
+static void
+trace(const char *const symbol)
+{
+    if (__cxa_demangle) {
+        // >If output_buffer is not long enough, it is expanded using realloc
+        // Holy fuck gcc what the fuck? Guess we don't use stack then, thanks
+        int status;
+        char *demangled;
+        if ((demangled = __cxa_demangle(symbol, NULL, NULL, &status))) {
+            printf("trace: %s\n", demangled);
+            free(demangled); // so pointless...
+            return;
+        }
+    }
+
+    printf("trace: %s\n", symbol);
+}
+#endif
+
+void*
+wrapper_create(const char *const symbol, void *function)
+{
+#ifdef WRAPPER_TRACE
+    if (!__cxa_demangle)
+        __cxa_demangle = dlsym(RTLD_DEFAULT, "__cxa_demangle");
+
+    const size_t sz = &wrapper_end - &wrapper_start;
+    unsigned char *fun = mmap(NULL, sz, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+    assert(fun != MAP_FAILED);
+    memcpy(fun, &wrapper_start, sz);
+#ifdef ANDROID_X86_LINKER
+    memcpy(fun + (&wrapper_symbol - &wrapper_start) + 1, &symbol, sizeof(symbol));
+    memcpy(fun + (&wrapper_trace - &wrapper_start) + 1, (uintptr_t[]){ (uintptr_t)trace }, sizeof(uintptr_t));
+    memcpy(fun + (&wrapper_call - &wrapper_start) + 1, &function, sizeof(function));
+#else
+#   error "should not happen"
+#endif
+    mprotect(fun, sz, PROT_READ | PROT_EXEC);
+    return fun;
+#else
+    return function;
+#endif
+}
diff --git a/src/wrapper/wrapper.h b/src/wrapper/wrapper.h
new file mode 100644
index 0000000..c75ef33
--- /dev/null
+++ b/src/wrapper/wrapper.h
@@ -0,0 +1,4 @@
+#pragma once
+
+void*
+wrapper_create(const char *const symbol, void *function);