Encoder: rename operand_count -> operand_count_visible

Resolves #458
zyantific · Oct 15, 2023 · 04c092c · 04c092c
1 parent 49fa4db
commit 04c092c
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Showing 3 changed files with 22 additions and 17 deletions.
diff --git a/assets/porting-guide-v4-v5.md b/assets/porting-guide-v4-v5.md
@@ -0,0 +1,7 @@
+# Porting Guide v4 -> v5
+
+# Encoder
+
+- `ZydisEncoderDecodedInstructionToEncoderRequest` now expects exactly `instruction->operand_count_visible` to be
+  passed, not `operand_count_visible` at maximum. Passing a lower value was previously allowed but didn't really
+  make much sense at all.
diff --git a/include/Zydis/Encoder.h b/include/Zydis/Encoder.h
@@ -312,7 +312,9 @@ typedef struct ZydisEncoderRequest_
      */
     ZydisOperandSizeHint operand_size_hint;
     /**
-     * The number of instruction-operands.
+     * The number of visible (explicit) instruction operands.
+     *
+     * The encoder does not care about hidden (implicit) operands.
      */
     ZyanU8 operand_count;
     /**
@@ -422,11 +424,11 @@ ZYDIS_EXPORT ZyanStatus ZydisEncoderEncodeInstructionAbsolute(ZydisEncoderReques
  * Converts decoded instruction to encoder request that can be passed to
  * `ZydisEncoderEncodeInstruction`.
  *
- * @param   instruction     A pointer to the `ZydisDecodedInstruction` struct.
- * @param   operands        A pointer to the decoded operands.
- * @param   operand_count   The operand count.
- * @param   request         A pointer to the `ZydisEncoderRequest` struct, that receives
- *                          information necessary for encoder to re-encode the instruction.
+ * @param   instruction             A pointer to the `ZydisDecodedInstruction` struct.
+ * @param   operands                A pointer to the decoded operands.
+ * @param   operand_count_visible   The number of visible instruction operands.
+ * @param   request                 A pointer to the `ZydisEncoderRequest` struct, that receives
+ *                                  information necessary for encoder to re-encode the instruction.
  *
  * This function performs simple structure conversion and does minimal sanity checks on the 
  * input. There's no guarantee that produced request will be accepted by
@@ -437,7 +439,7 @@ ZYDIS_EXPORT ZyanStatus ZydisEncoderEncodeInstructionAbsolute(ZydisEncoderReques
  */
 ZYDIS_EXPORT ZyanStatus ZydisEncoderDecodedInstructionToEncoderRequest(
     const ZydisDecodedInstruction* instruction, const ZydisDecodedOperand* operands,
-    ZyanU8 operand_count, ZydisEncoderRequest* request);
+    ZyanU8 operand_count_visible, ZydisEncoderRequest* request);
 
 /**
  * Fills provided buffer with `NOP` instructions using longest possible multi-byte instructions.

diff --git a/src/Encoder.c b/src/Encoder.c
@@ -4525,10 +4525,11 @@ ZYDIS_EXPORT ZyanStatus ZydisEncoderEncodeInstructionAbsolute(ZydisEncoderReques
 }
 
 ZYDIS_EXPORT ZyanStatus ZydisEncoderDecodedInstructionToEncoderRequest(
-    const ZydisDecodedInstruction *instruction, const ZydisDecodedOperand* operands, 
-    ZyanU8 operand_count, ZydisEncoderRequest *request)
+        const ZydisDecodedInstruction *instruction, const ZydisDecodedOperand* operands,
+        ZyanU8 operand_count_visible, ZydisEncoderRequest *request)
 {
-    if (!instruction || !request || (operand_count && !operands))
+    if (!instruction || !request || (operand_count_visible && !operands) ||
+        operand_count_visible != instruction->operand_count_visible)
     {
         return ZYAN_STATUS_INVALID_ARGUMENT;
     }
@@ -4635,13 +4636,8 @@ ZYDIS_EXPORT ZyanStatus ZydisEncoderDecodedInstructionToEncoderRequest(
     }
     request->allowed_encodings = 1 << instruction->encoding;
 
-    if ((operand_count > ZYDIS_ENCODER_MAX_OPERANDS) || 
-        (operand_count > instruction->operand_count_visible))
-    {
-        return ZYAN_STATUS_INVALID_ARGUMENT;
-    }
-    request->operand_count = operand_count;
-    for (ZyanU8 i = 0; i < operand_count; ++i)
+    request->operand_count = operand_count_visible;
+    for (ZyanU8 i = 0; i < operand_count_visible; ++i)
     {
         const ZydisDecodedOperand *dec_op = &operands[i];
         ZydisEncoderOperand *enc_op = &request->operands[i];