intel/gen_decoder: return -1 for unknown command formats

Decoding with aubinator encountered a command of 0xffffffff. With the
previous code, it caused aubinator to jump 255 + 2 dwords to start
decoding again.

Instead we can attempt to detect the known instruction formats. If the
format is not recognized, then we can advance just 1 dword.

v2:
 * Update aubinator_error_decode
 * Actually convert the length variable returned into a *signed* integer
   in aubinator.c, intel_batchbuffer.c and aubinator_error_decode.c.

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Acked-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>

src/intel/tools/aubinator.c

@@ -682,17 +682,18 @@ static void
 parse_commands(struct gen_spec *spec, uint32_t *cmds, int size, int engine)
 {
    uint32_t *p, *end = cmds + size / 4;
-   unsigned int length, i;
+   int length, i;
    struct gen_group *inst;
 
    for (p = cmds; p < end; p += length) {
       inst = gen_spec_find_instruction(spec, p);
+      length = gen_group_get_length(inst, p);
+      assert(inst == NULL || length > 0);
+      length = MAX2(1, length);
       if (inst == NULL) {
          fprintf(outfile, "unknown instruction %08x\n", p[0]);
-         length = (p[0] & 0xff) + 2;
          continue;
       }
-      length = gen_group_get_length(inst, p);
 
       const char *color, *reset_color = NORMAL;
       uint64_t offset;

src/intel/tools/aubinator_error_decode.c

@@ -217,7 +217,7 @@ static void decode(struct gen_spec *spec,
                    int *count)
 {
    uint32_t *p, *end = (data + *count);
-   unsigned int length;
+   int length;
    struct gen_group *inst;
 
    for (p = data; p < end; p += length) {
@@ -226,9 +226,11 @@ static void decode(struct gen_spec *spec,
       uint64_t offset = gtt_offset + 4 * (p - data);
 
       inst = gen_spec_find_instruction(spec, p);
+      length = gen_group_get_length(inst, p);
+      assert(inst == NULL || length > 0);
+      length = MAX2(1, length);
       if (inst == NULL) {
          printf("unknown instruction %08x\n", p[0]);
-         length = (p[0] & 0xff) + 2;
          continue;
       }
       if (option_color == COLOR_NEVER) {
@@ -241,7 +243,6 @@ static void decode(struct gen_spec *spec,
 
       gen_print_group(stdout, inst, offset, p,
                       option_color == COLOR_ALWAYS);
-      length = gen_group_get_length(inst, p);
    }
 }