From 545ec30ad0592d63cbcff482e877db96739a72f8 Mon Sep 17 00:00:00 2001
From: Alexis Engelke <alexis.engelke@googlemail.com>
Date: Sun, 14 Jun 2020 14:01:39 +0200
Subject: [PATCH] decode: Return partial error on incomplete opcode

---
 decode.c             |  2 +-
 tests/decode-jmp.txt |  2 ++
 tests/driver.c       | 26 +++++++++++++++++---------
 tests/prefixes.txt   |  3 +++
 4 files changed, 23 insertions(+), 10 deletions(-)

diff --git a/decode.c b/decode.c
index ad880de..070aad6 100644
--- a/decode.c
+++ b/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;
 
diff --git a/tests/decode-jmp.txt b/tests/decode-jmp.txt
index 7999c32..9bc7937 100644
--- a/tests/decode-jmp.txt
+++ b/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
diff --git a/tests/driver.c b/tests/driver.c
index acc44cb..2e1c413 100644
--- a/tests/driver.c
+++ b/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");
 
-    char format_buffer[128];
-    fd_format(&instr, format_buffer, sizeof(format_buffer));
-    printf("%s\n", format_buffer);
+    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;
 }
diff --git a/tests/prefixes.txt b/tests/prefixes.txt
index dc6eb5d..02714d8 100644
--- a/tests/prefixes.txt
+++ b/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