undo change to x86_64 injector

Revert "make the x86_64 injector slightly more efficient"

This reverts commit a613c19.

inject-x86_64.c

@@ -103,10 +103,12 @@ void injectSharedLibrary(long mallocaddr, long freeaddr, long dlopenaddr)
 		// call free()
 		"callq *%rbx \n"
 		// restore previous rbx value
-		"pop %rbx \n"
-		// give control back to the injector for the last time
-		"int $3"
+		"pop %rbx"
 	);
+
+	// we already overwrote the RET instruction at the end of this function
+	// with an INT 3, so at this point the injector will regain control of
+	// the target's execution.
 }
 
 /*
@@ -208,11 +210,7 @@ int main(int argc, char** argv)
 	// it. we have to advance by 2 bytes here because rip gets incremented
 	// by the size of the current instruction, and the instruction at the
 	// start of the function to inject always happens to be 2 bytes long.
-	//
-	// after that, we advance by 15 more bytes in order to skip the
-	// function prologue generated by the compiler, which unnecessarily
-	// saves the previous values of rdi, rsi, and edx on the stack.
-	regs.rip = addr + 2 + 15;
+	regs.rip = addr + 2;
 
 	// pass arguments to my function injectSharedLibrary() by loading them
 	// into the right registers. note that this will definitely only work
@@ -248,6 +246,8 @@ int main(int argc, char** argv)
 
 	// copy the code of injectSharedLibrary() to a buffer.
 	memcpy(newcode, injectSharedLibrary, injectSharedLibrary_size - 1);
+	// overwrite the RET instruction with an INT 3.
+	newcode[injectSharedLibrary_ret] = INTEL_INT3_INSTRUCTION;
 
 	// copy injectSharedLibrary()'s code to the target address inside the
 	// target process' address space.