decode: Return partial error on incomplete opcode

decode.c

@@ -416,7 +416,7 @@ fd_decode(const uint8_t* buffer, size_t len_sz, int mode_int, uintptr_t address,
     }
 
     if (UNLIKELY(kind != ENTRY_INSTR))
-        return FD_ERR_UD;
+        return kind == 0 ? FD_ERR_UD : FD_ERR_PARTIAL;
 
     struct InstrDesc* desc = (struct InstrDesc*) table;
 

tests/decode-jmp.txt

@@ -2,3 +2,5 @@ decode32 e900000000                     [JMP off4:eip+0x0]
 decode32 66e90100                       [JMP off2:ip+0x1]
 decode64 e900000000                     [JMP off8:rip+0x0]
 decode64 66e900000000                   [JMP off8:rip+0x0]
+decode   66e9000000                     PARTIAL
+decode   66e9                           PARTIAL

tests/driver.c

@@ -49,6 +49,7 @@ main(int argc, char** argv)
     struct timespec time_end;
 
     FdInstr instr;
+    int retval = 0;
 
     __asm__ volatile("" : : : "memory");
     clock_gettime(CLOCK_MONOTONIC, &time_start);
@@ -58,18 +59,29 @@ main(int argc, char** argv)
         while (current_off != length)
         {
             size_t remaining = length - current_off;
-            int retval = fd_decode(code + current_off, remaining, mode, 0, &instr);
+            retval = fd_decode(code + current_off, remaining, mode, 0, &instr);
             if (retval < 0)
-                goto fail;
+                break;
             current_off += retval;
         }
     }
     clock_gettime(CLOCK_MONOTONIC, &time_end);
     __asm__ volatile("" : : : "memory");
 
+    if (retval >= 0)
+    {
         char format_buffer[128];
         fd_format(&instr, format_buffer, sizeof(format_buffer));
         printf("%s\n", format_buffer);
+    }
+    else if (retval == FD_ERR_UD)
+    {
+        printf("UD\n");
+    }
+    else if (retval == FD_ERR_PARTIAL)
+    {
+        printf("PARTIAL\n");
+    }
 
     if (repetitions > 1)
     {
@@ -80,8 +92,4 @@ main(int argc, char** argv)
     }
 
     return 0;
-
-fail:
-    puts("Decoding failed.");
-    return 1;
 }

tests/prefixes.txt

@@ -14,3 +14,6 @@ decode   f266f3660f10c1                 [SSE_MOVSS reg4:r0 reg4:r1]
 decode64 4890                           [NOP]
 decode64 4990                           [XCHG reg8:r8 reg8:r0]
 decode64 6690                           [NOP]
+decode   66                             PARTIAL
+decode   0f                             PARTIAL
+decode   80                             PARTIAL