add new TRAMPOLINE macro

README.md

@@ -168,6 +168,28 @@ Example:
        something();
     }
 
+You can also keep the original function intact by clearing only the first 
+instructions (just to make enough space for the 5 byte jump to fit) and afterwards 
+create a trampoline in sym.c to restore the instructions that were removed.
+
+    /* Clear first two instructions AND do a (far) jump from 0x410000 to label doMagic */`
+    DETOUR(0x410000, 0x410007, _doMagic);
+
+    EXTERN_C void doMagic(int arg1, int arg2, int arg3)
+    {
+       /* insert your own code here */
+       something();
+
+       /* call the orginal function that was replaced by the patch (optional) */
+       original(arg1, arg2, arg3);
+    }
+
+    /* sym.c - Create trampoline to restore the two instuctions removed by DETOUR */
+    TRAMPOLINE(0x410007, original, "sub esp, 8; mov eax, [esp+0x1C]");
+
+    /* Same as above, but for functions using the watcom register calling convention */
+    TRAMPOLINE(0x410007, original, "sub esp, 8; mov eax, [esp+0x1C]", 3);
+
 Note: the `DETOUR` macro is NOT available for `NASM` and `GNU as` but the same can be done via `@HOOK` instead
 
 ### Hook

res/inc/macros/patch.inc

@@ -89,29 +89,6 @@
     dest%1:
 %endmacro
 
-%macro @DETOUR 3
-    cglobal %1
-    %define @DETOUREND (%3 + 5)
-    @LJMP {(%3)}, %2
-    [section .text]
-    align 16, db 0xCC
-    %1:
-%endmacro
-
-%macro @DETOUR 4
-    cglobal %1
-    %define @DETOUREND %4
-    %if %4 - ((%3) + 5) < 0
-        %error "end must be at least 5 bytes (the size of a long jump) after start"
-    %endif
-
-    @CLEAR {(%3) + 5}, 0xCC, {(%4)}
-    @LJMP {(%3)}, %2
-    [section .text]
-    align 16, db 0xCC
-    %1:
-%endmacro
-
 %macro @CLEAR_NOP 2
     @CLEAR %1, 0x90, %2
 %endmacro

res/inc/macros/setsym.h

@@ -1,17 +1,4 @@
-#define SETCGLOB_2(addr, name)                       \
-    __asm (                                          \
-        ".global _" #name ";"                        \
-        ".equ _" #name ", " #addr ";"                \
-    )
-
-#define SETCGLOB_3(addr, name, arg_count)            \
-    __asm (                                          \
-        ".global _" #name ";"                        \
-        ".global " #name ";"                         \
-        ".equ " #name ", " #addr ";"                 \
-        ".section .text;"                            \
-        ".align 8, 0xCC;"                            \
-        "_" #name ":;"                               \
+#define CDECL_TO_WATCALL(addr, arg_count)            \
         "push ebx;"                                  \
         "push ebp;"                                  \
         "mov ebp, esp;"                              \
@@ -66,7 +53,23 @@
         "call " #addr ";"                            \
         "pop ebp;"                                   \
         "pop ebx;"                                   \
-        "ret;"                                       \
+        "ret;"
+
+#define SETCGLOB_2(addr, name)                       \
+    __asm (                                          \
+        ".global _" #name ";"                        \
+        ".equ _" #name ", " #addr ";"                \
+    )
+
+#define SETCGLOB_3(addr, name, arg_count)            \
+    __asm (                                          \
+        ".global _" #name ";"                        \
+        ".global " #name ";"                         \
+        ".equ " #name ", " #addr ";"                 \
+        ".section .text;"                            \
+        ".align 8, 0xCC;"                            \
+        "_" #name ":;"                               \
+        CDECL_TO_WATCALL(addr, arg_count)            \
     )
 
 #define SETCGLOB_X(x,A,B,C,FUNC, ...)  FUNC  
@@ -77,3 +80,37 @@
                             SETCGLOB_1(__VA_ARGS__), \
                             SETCGLOB_0(__VA_ARGS__)  \
                             )
+
+#define TRAMPOLINE_3(addr, name, inst)               \
+    __asm (                                          \
+        ".global _" #name ";"                        \
+        ".section .text;"                            \
+        ".align 8, 0xCC;"                            \
+        "_" #name ":;"                               \
+        inst ";"                                     \
+        "jmp " #addr ";"                             \
+    )
+
+#define TRAMPOLINE_4(addr, name, inst, arg_count)    \
+    __asm (                                          \
+        ".global _" #name ";"                        \
+        ".global " #name ";"                         \
+        ".section .text;"                            \
+        ".align 8, 0xCC;"                            \
+        #name ":;"                                   \
+        inst ";"                                     \
+        "jmp " #addr ";"                             \
+        ".align 8, 0xCC;"                            \
+        "_" #name ":;"                               \
+        CDECL_TO_WATCALL(name, arg_count)            \
+    )
+
+#define TRAMPOLINE_X(x,A,B,C,D,FUNC, ...)  FUNC  
+#define TRAMPOLINE(...)                              \
+                     TRAMPOLINE_X(,##__VA_ARGS__,    \
+                          TRAMPOLINE_4(__VA_ARGS__), \
+                          TRAMPOLINE_3(__VA_ARGS__), \
+                          TRAMPOLINE_2(__VA_ARGS__), \
+                          TRAMPOLINE_1(__VA_ARGS__), \
+                          TRAMPOLINE_0(__VA_ARGS__)  \
+                          )

res/inc/patch.h

@@ -112,7 +112,7 @@ static inline void patch_ljmp_int(char *start, char *end, char *dst)
     patch_ljmp(start, dst);
 }
 
-static inline void patch_detour(char* start, char* end, char* dst)
+static inline void patch_detour(char *start, char *end, char *dst)
 {
     patch_clear(start + 5, '\xCC', end);
     patch_ljmp(start, dst);