[PATCH] gas: m68k M680LC040 F-LINE NOP insertion fixing emulation of fpu instructions

[Nathanial Sloss]

Hi,

The m68k m68lc040 (early revisions) have an issue after executing f-line (co 
processor mmu/fpu) instructions and executing a trap in the case of fpu 
emulation.

Unfornately due to time passed the processor errata as to how to address the 
issue has been lost.

Fortunately the issue was documented in a NetBSD PR:

http://gnats.netbsd.org/13078

Which proposes a solution to the problem which I have patched the GNU 
assembler for.

As I have an affected machine with an lc040 processor I can confirm that all 
programmes compiled with the patched assember work as expected.


Best regards,

Nat

--- a/external/gpl3/binutils/dist/gas/config/tc-m68k.c	Sun Dec 01 20:36:00 2024 +0000
+++ b/external/gpl3/binutils/dist/gas/config/tc-m68k.c	Mon Dec 02 19:03:37 2024 +1100
@@ -74,6 +74,7 @@
 static int flag_short_refs;	/* -l option.  */
 static int flag_long_jumps;	/* -S option.  */
 static int flag_keep_pcrel;	/* --pcrel option.  */
+static bool lcfix = true;
 
 #ifdef REGISTER_PREFIX_OPTIONAL
 int flag_reg_prefix_optional = REGISTER_PREFIX_OPTIONAL;
@@ -4272,8 +4273,24 @@
 	}
     }
 
+  bool hasnop = false;
+  char nop[4] = "nop";
+  toP = NULL;
+next:
   memset (&the_ins, '\0', sizeof (the_ins));
+
   m68k_ip (str);
+
+  if (lcfix == true && hasnop == false &&
+       (the_ins.opcode[0] & 0xf000) == 0xf000)
+    {
+      memset (&the_ins, '\0', sizeof (the_ins));
+      m68k_ip (nop);
+      hasnop = true;
+    }
+  else
+    hasnop = false;
+
   er = the_ins.error;
   if (!er)
     {
@@ -4349,6 +4366,8 @@
 	  if (the_ins.reloc[m].wid == 'B')
 	    fixP->fx_signed = 1;
 	}
+      if (hasnop == true)
+	goto next;
       return;
     }
 
@@ -4447,6 +4466,8 @@
 					  the_ins.reloc[m].pic_reloc));
       fixP->fx_pcrel_adjust = the_ins.reloc[m].pcrel_fix;
     }
+  if (hasnop == true)
+    goto next;
 }
 
 /* Comparison function used by qsort to rank the opcode entries by name.  */
@@ -7455,6 +7476,8 @@
 	;
       else if (m68k_set_cpu (arg, 0, 1))
 	;
+      else if (startswith (arg, "no-lcfix"))
+	lcfix = false;
       else
 	return 0;
       break;
@@ -7556,6 +7579,7 @@
   fprintf (stream, _("\
 -march=<arch>		set architecture\n\
 -mcpu=<cpu>		set cpu [default %s]\n\
+-mno-lcfix		no compatability with lc040 nop before f-line\n\
 "), default_cpu);
   for (i = 0; m68k_extensions[i].name; i++)
     fprintf (stream, _("\