begin working on rt_target search - we need that for syscall trampolines

include/rtdisasm.h

@@ -2,12 +2,20 @@
 #define __RTDISASM_H
 
 #include <stdint.h>
+#include "rtdisasm_table.h"
 
-// code should point to place with machine instructions, and size
+// "code" should point to place with machine instructions, and "size"
 // limits the area of analyze, so no segfaults would be triggered on
-// page boundaries.
+// page boundaries. if "found" is non-zero, on instruction hit it
+// would be set to found instruction table entry
 // returns 0 when no instruction was found, -1 when size limit reached
 // and non-negative-non-zero number of actual instruction size
-int rtdisasm_analyze_single(const uint8_t* code, uint8_t size);
+int rtdisasm_analyze_single(const uint8_t* code, unsigned size, const instruction_t** found);
+
+// analyze all instructions at "code" until "size" limit is reached or
+// instruction of "rt_target" equal was found. returns -1 when size limit hit,
+// 0 if rtdisasm encountered unknown instruction
+// and non-zero integer is offset from "code"
+int rtdisasm_find_target(const uint8_t* code, unsigned size, unsigned rt_target);
 
 #endif

src/rtdisasm.c

@@ -231,7 +231,7 @@ static void print_opcodes(const instruction_t* ins)
 #define print_opcodes(ins)
 #endif
 
-int rtdisasm_analyze_single(const uint8_t* code, uint8_t size)
+int rtdisasm_analyze_single(const uint8_t* code, unsigned size, const instruction_t** found)
 {
     const uint8_t* cur = code;
     const uint8_t* const end = code + size;
@@ -311,6 +311,35 @@ int rtdisasm_analyze_single(const uint8_t* code, uint8_t size)
         if (cur >= end) return -1;
     }
 
+    // set found
+    if (found) *found = ins;
     // return length of entire decoded instruction
     return (int)((uintptr_t)cur-(uintptr_t)code);
 }
+
+int rtdisasm_find_target(const uint8_t* code, unsigned size, unsigned rt_target)
+{
+    const uint8_t* cur = code;
+    const uint8_t* const end = code + size;
+    unsigned remaining = size;
+    if (cur == end) return -1;
+
+    do {
+        const instruction_t* ins;
+        int len = rtdisasm_analyze_single(cur, remaining, &ins);
+        // NOTE: this is ret passthru from analyze single,
+        // so it must be follow same ret logic as this function
+        if (len < 1) return len;
+
+        if (ins->rt_target == rt_target)
+        {
+            // we found target instruction!
+            return (int)((uintptr_t)cur-(uintptr_t)code);
+        }
+
+        // otherwise, advance further
+        cur += len;
+        remaining -= len;
+        if (cur >= end) return -1;
+    } while (1);
+}

src/rtdisasm_test.c

@@ -7,8 +7,10 @@ extern void test_1_end();
 int main()
 {
     size_t size = (uintptr_t)test_1_end - (uintptr_t)test_1;
-    int len = rtdisasm_analyze_single((const uint8_t*)test_1, size);
+    int len = rtdisasm_analyze_single((const uint8_t*)test_1, size, NULL);
+    printf("rtdisasm_analyze_single: len %d\n", len);
 
-    printf("len %d\n", len);
+    int offset = rtdisasm_find_target((const uint8_t*)test_1, size, RT_TARGET_NOP);
+    printf("rtdisasm_find_target: offset %d\n", offset);
     return 0;
 }