Change the prototype of the callback in SKIPDATA option. Suggested by Ben Nagy.

Original prototype:
  typedef size_t (*cs_skipdata_cb_t)(const uint8_t *code, uint64_t offset, void* user_data);

Now we add @code_size argument to reflect the size of the input buffer @code.
Also, we change the data type of @offset to size_t because this argument indicates the
distance from currently examining bytes to @code, but not the address of the byte.

  typedef size_t (*cs_skipdata_cb_t)(const uint8_t *code, size_t code_size, size_t offset, void* user_data);

cs.c

@@ -422,7 +422,10 @@ size_t cs_disasm_ex(csh ud, const uint8_t *buffer, size_t size, uint64_t offset,
 	bool r;
 	void *tmp;
 	size_t skipdata_bytes;
+	// save all the original info of the buffer
 	uint64_t offset_org;
+	size_t size_org;
+	const uint8_t *buffer_org;
 
 	if (!handle) {
 		// FIXME: how to handle this case:
@@ -433,7 +436,9 @@ size_t cs_disasm_ex(csh ud, const uint8_t *buffer, size_t size, uint64_t offset,
 	handle->errnum = CS_ERR_OK;
 
 	// save the original offset for SKIPDATA
+	buffer_org = buffer;
 	offset_org = offset;
+	size_org = size;
 	total_size = (sizeof(cs_insn) * INSN_CACHE_SIZE);
 	total = cs_mem_malloc(total_size);
 	insn_cache = total;
@@ -512,8 +517,8 @@ size_t cs_disasm_ex(csh ud, const uint8_t *buffer, size_t size, uint64_t offset,
 				break;
 
 			if (handle->skipdata_setup.callback) {
-				skipdata_bytes = handle->skipdata_setup.callback(buffer, offset - offset_org,
-						handle->skipdata_setup.user_data);
+				skipdata_bytes = handle->skipdata_setup.callback(buffer_org, size_org,
+						offset - offset_org, handle->skipdata_setup.user_data);
 				if (skipdata_bytes > size)
 					// remaining data is not enough
 					break;

include/capstone.h

@@ -116,12 +116,13 @@ typedef enum cs_opt_value {
 // User-defined callback function for SKIPDATA option
 // @code: the input buffer containing code to be disassembled. This is the 
 //      same buffer passed to cs_disasm_ex().
+// @code_size: size (in bytes) of the above @code buffer.
 // @offset: the position of the currently-examining byte in the input
 //      buffer @code mentioned above.
 // @user_data: user-data passed to cs_option() via @user_data field in
 //      cs_opt_skipdata struct below.
 // @return: return number of bytes to skip, or 0 to immediately stop disassembling.
-typedef size_t (*cs_skipdata_cb_t)(const uint8_t *code, uint64_t offset, void* user_data);
+typedef size_t (*cs_skipdata_cb_t)(const uint8_t *code, size_t code_size, size_t offset, void* user_data);
 
 // User-customized setup for SKIPDATA option
 typedef struct cs_opt_skipdata {

tests/test_skipdata.c

@@ -30,17 +30,12 @@ static void print_string_hex(unsigned char *str, int len)
 	printf("\n");
 }
 
-size_t mycallback(const uint8_t *buffer, uint64_t offset, void *p)
+static size_t mycallback(const uint8_t *buffer, size_t buffer_size, size_t offset, void *p)
 {
 	// always skip 2 bytes when encountering data
 	return 2;
 }
 
-cs_opt_skipdata skipdata = {
-	// rename default "data" instruction from ".byte" to "db"
-	"db",
-};
-
 static void test()
 {
 #define X86_CODE32 "\x8d\x4c\x32\x08\x01\xd8\x81\xc6\x34\x12\x00\x00\x00\x91\x92"