From dc55b81456e408850a44f8368819d41d50cc02d8 Mon Sep 17 00:00:00 2001
From: Jari Vetoniemi <mailroxas@gmail.com>
Date: Thu, 22 Nov 2018 10:11:01 +0200
Subject: refactor trampoline to use relative jmp/call

---
 src/wrapper/wrapper.c | 33 +++++++++++++++++++++++++--------
 1 file changed, 25 insertions(+), 8 deletions(-)

diff --git a/src/wrapper/wrapper.c b/src/wrapper/wrapper.c
index 5b319f3..8ce6ffb 100644
--- a/src/wrapper/wrapper.c
+++ b/src/wrapper/wrapper.c
@@ -34,9 +34,12 @@ verbose_log(const char *fmt, ...)
 #  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_store: push %edi\npush %esp\npush %ebp\npush %ebx\npush %eax\npush %ecx\npush %edx\n"
+   "wrapper_symbol: pushl $0xFAFBFCFD\n" // arg1 for trace
+   "wrapper_trace: .byte 0xE8, 0xFA, 0xFB, 0xFC, 0xFD\n" // CALL (trace)
+   "wrapper_restore: pop %eax\npop %edx\npop %ecx\npop %eax\npop %ebx\npop %ebp\npop %esp\npop %edi\n"
+   "wrapper_jmp: .byte 0xE9, 0xFA, 0xFB, 0xFC, 0xFD\n" // JMP
+   "wrapper_ud: .byte 0x0F, 0xFF\n" // UD
    "wrapper_end: nop\n"
 );
 #     define WRAPPER_TRACE
@@ -46,7 +49,7 @@ __asm__(
 #endif
 
 #ifdef WRAPPER_TRACE
-extern char wrapper_start, wrapper_symbol, wrapper_trace, wrapper_call, wrapper_end;
+extern unsigned char wrapper_start, wrapper_symbol, wrapper_trace, wrapper_restore, wrapper_jmp, wrapper_ud, wrapper_end;
 
 static union {
    void *ptr;
@@ -104,9 +107,16 @@ wrapper_create(const char *const symbol, void *function)
       return NULL;
    }
 
+   return function;
+
 #ifdef WRAPPER_TRACE
+   static const union {
+      void *ptr;
+      void (*fun)(const char*);
+   } tracefun = { .fun = trace };
+
    const size_t len = strlen(symbol) + 1;
-   char *copy = malloc(len);
+   const char *copy = malloc(len);
    assert(copy && "welp, malloc failed");
    memcpy(copy, symbol, len);
    const size_t sz = &wrapper_end - &wrapper_start;
@@ -114,9 +124,16 @@ wrapper_create(const char *const symbol, void *function)
    assert(fun != MAP_FAILED);
    memcpy(fun, &wrapper_start, sz);
 #ifdef ANDROID_X86_LINKER
-   memcpy(fun + (&wrapper_symbol - &wrapper_start) + 1, &copy, 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));
+   memcpy(fun + (&wrapper_symbol - &wrapper_start) + 1, &copy, sizeof(copy));
+   {
+      const unsigned char *from = fun + (&wrapper_restore - &wrapper_start);
+      const unsigned char *to = (unsigned char*)tracefun.ptr - from;
+      memcpy(fun + (&wrapper_trace - &wrapper_start) + 1, &to, sizeof(to));
+   }{
+      const unsigned char *from = fun + (&wrapper_ud - &wrapper_start);
+      const unsigned char *to = (unsigned char*)function - from;
+      memcpy(fun + (&wrapper_jmp - &wrapper_start) + 1, &to, sizeof(to));
+   }
 #else
 #   error "you forgot to implement the pointer setups for your asm platform"
 #endif
-- 
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