[PATCH] FT32: support for FT32B processor - part 2/2

[James Bowman <james dot bowman at ftdichip dot com>]

FT32B is a new FT32 family member. It has a code
compression scheme, which requires the use of linker
relaxations. The change is quite large, so submission
is in several parts.

Part 2 adds support for the compressed instructions to gdb and sim.

This patch contains the gdb changes. The corresponding binutils patch is
https://sourceware.org/ml/binutils/2017-10/msg00423.html

OK to commit?

James.

gdb/ChangeLog:

2017-10-29  James Bowman  <james.bowman@ftdichip.com>

	* ft32-tdep.c (ft32_fetch_instruction): New function.
	(ft32_analyze_prologue): Use ft32_fetch_instruction().

sim/ChangeLog:

2017-10-29  James Bowman  <james.bowman@ftdichip.com>

	* ft32/interp.c (step_once): Add ft32 shortcode decoder.

---
diff --git a/gdb/ft32-tdep.c b/gdb/ft32-tdep.c
index 757301a..00aba23 100644
--- a/gdb/ft32-tdep.c
+++ b/gdb/ft32-tdep.c
@@ -139,6 +139,22 @@ ft32_store_return_value (struct type *type, struct regcache *regcache,
     }
 }
 
+static ULONGEST
+ft32_fetch_instruction (CORE_ADDR a, int *isize,
+		        enum bfd_endian byte_order)
+{
+  unsigned int sc[2];
+  ULONGEST inst;
+
+  CORE_ADDR a4 = a & ~3;
+  inst = read_memory_unsigned_integer (a4, 4, byte_order);
+  *isize = ft32_decode_shortcode (a4, inst, sc) ? 2 : 4;
+  if (*isize == 2)
+    return sc[1 & (a >> 1)];
+  else
+    return inst;
+}
+
 /* Decode the instructions within the given address range.  Decide
    when we must have reached the end of the function prologue.  If a
    frame_info pointer is provided, fill in its saved_regs etc.
@@ -153,6 +169,7 @@ ft32_analyze_prologue (CORE_ADDR start_addr, CORE_ADDR end_addr,
   enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
   CORE_ADDR next_addr;
   ULONGEST inst;
+  int isize = 0;
   int regnum, pushreg;
   struct bound_minimal_symbol msymbol;
   const int first_saved_reg = 13;	/* The first saved register.  */
@@ -186,16 +203,15 @@ ft32_analyze_prologue (CORE_ADDR start_addr, CORE_ADDR end_addr,
     return end_addr;
 
   cache->established = 0;
-  for (next_addr = start_addr; next_addr < end_addr;)
+  for (next_addr = start_addr; next_addr < end_addr; next_addr += isize)
     {
-      inst = read_memory_unsigned_integer (next_addr, 4, byte_order);
+      inst = ft32_fetch_instruction (next_addr, &isize, byte_order);
 
       if (FT32_IS_PUSH (inst))
 	{
 	  pushreg = FT32_PUSH_REG (inst);
 	  cache->framesize += 4;
 	  cache->saved_regs[FT32_R0_REGNUM + pushreg] = cache->framesize;
-	  next_addr += 4;
 	}
       else if (FT32_IS_CALL (inst))
 	{
@@ -210,7 +226,6 @@ ft32_analyze_prologue (CORE_ADDR start_addr, CORE_ADDR end_addr,
 		      cache->saved_regs[FT32_R0_REGNUM + pushreg] =
 			cache->framesize;
 		    }
-		  next_addr += 4;
 		}
 	    }
 	  break;
@@ -229,7 +244,7 @@ ft32_analyze_prologue (CORE_ADDR start_addr, CORE_ADDR end_addr,
   /* It is a LINK?  */
   if (next_addr < end_addr)
     {
-      inst = read_memory_unsigned_integer (next_addr, 4, byte_order);
+      inst = ft32_fetch_instruction (next_addr, &isize, byte_order);
       if (FT32_IS_LINK (inst))
 	{
 	  cache->established = 1;
@@ -241,7 +256,7 @@ ft32_analyze_prologue (CORE_ADDR start_addr, CORE_ADDR end_addr,
 	  cache->saved_regs[FT32_PC_REGNUM] = cache->framesize + 4;
 	  cache->saved_regs[FT32_FP_REGNUM] = 0;
 	  cache->framesize += FT32_LINK_SIZE (inst);
-	  next_addr += 4;
+	  next_addr += isize;
 	}
     }
 
diff --git a/sim/ft32/interp.c b/sim/ft32/interp.c
index 3bc08ee..b3dded1 100644
--- a/sim/ft32/interp.c
+++ b/sim/ft32/interp.c
@@ -340,16 +340,24 @@ step_once (SIM_DESC sd)
   uint32_t bit_len;
   uint32_t upper;
   uint32_t insnpc;
+  unsigned int sc[2];
+  int isize;
 
-  if (cpu->state.cycles >= cpu->state.next_tick_cycle)
-    {
-      cpu->state.next_tick_cycle += 100000;
-      ft32_push (sd, cpu->state.pc);
-      cpu->state.pc = 12;  /* interrupt 1.  */
-    }
   inst = ft32_read_item (sd, 2, cpu->state.pc);
   cpu->state.cycles += 1;
 
+  if ((STATE_ARCHITECTURE (sd)->mach == bfd_mach_ft32b)
+      && ft32_decode_shortcode (cpu->state.pc, inst, sc))
+    {
+      if ((cpu->state.pc & 3) == 0)
+        inst = sc[0];
+      else
+        inst = sc[1];
+      isize = 2;
+    }
+  else
+    isize = 4;
+
   /* Handle "call 8" (which is FT32's "break" equivalent) here.  */
   if (inst == 0x00340002)
     {
@@ -390,7 +398,7 @@ step_once (SIM_DESC sd)
   upper = (inst >> 27);
 
   insnpc = cpu->state.pc;
-  cpu->state.pc += 4;
+  cpu->state.pc += isize;
   switch (upper)
     {
     case FT32_PAT_TOC: