x86: warn about insns exceeding the 15-byte limit

Such insns will cause #UD when an attempt to execute them is made.

See also http://www.sandpile.org/x86/opc_enc.htm.

1 files changed, 32 insertions, 0 deletions

diff --git a/gas/config/tc-i386.c b/gas/config/tc-i386.c
index 4e55188..84c4bc5 100644
--- a/gas/config/tc-i386.c
+++ b/gas/config/tc-i386.c
@@ -8123,6 +8123,25 @@ x86_cleanup (void)
 }
 #endif
 
+static unsigned int
+encoding_length (const fragS *start_frag, offsetT start_off,
+		 const char *frag_now_ptr)
+{
+  unsigned int len = 0;
+
+  if (start_frag != frag_now)
+    {
+      const fragS *fr = start_frag;
+
+      do {
+	len += fr->fr_fix;
+	fr = fr->fr_next;
+      } while (fr && fr != frag_now);
+    }
+
+  return len - start_off + (frag_now_ptr - frag_now->fr_literal);
+}
+
 static void
 output_insn (void)
 {
@@ -8400,6 +8419,19 @@ output_insn (void)
 
       if (i.imm_operands)
 	output_imm (insn_start_frag, insn_start_off);
+
+      /*
+       * frag_now_fix () returning plain abs_section_offset when we're in the
+       * absolute section, and abs_section_offset not getting updated as data
+       * gets added to the frag breaks the logic below.
+       */
+      if (now_seg != absolute_section)
+	{
+	  j = encoding_length (insn_start_frag, insn_start_off, frag_more (0));
+	  if (j > 15)
+	    as_warn (_("instruction length of %u bytes exceeds the limit of 15"),
+		     j);
+	}
     }
 
 #ifdef DEBUG386