[RFC/TileGX 1/2] fix hand-written backtracer bug

[Jiong Wang <jiwang at tilera dot com>]

  noramlly, tilegx gcc always generate unwind table, so dwarf unwinder 
invoked
instead of hand-written unwinder, thus this bug is not triggered.

  but if the the user remove those unwind table from the elf files, for 
example,
specify -fno-asynchronous-unwind-tables, then tilegx gdb backtracer can 
not work.

  the reason is, tilegx hand-written backtracer did not handle the 
situation when
"lr", the return address is saved on stack.

gdb/ChangeLog:

        * tilegx-tdep.c (tilegx_analyze_prologue): add check for
        for return address, "lr" register, saved on stack.
        * tilegx-tdep.c (tilegx_frame_cache): update "PC" reg
        after we invoke tilegx_analyze_prologue.

please review.

thanks.

--
Regards,
Jiong. Wang
Tilera Corporation.

---
 gdb/tilegx-tdep.c |   19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/gdb/tilegx-tdep.c b/gdb/tilegx-tdep.c
index 0c560ba..c74f527 100644
--- a/gdb/tilegx-tdep.c
+++ b/gdb/tilegx-tdep.c
@@ -405,7 +405,7 @@ tilegx_analyze_prologue (struct gdbarch* gdbarch,
   struct tilegx_reverse_regs
     new_reverse_frame[TILEGX_MAX_INSTRUCTIONS_PER_BUNDLE];
   int dest_regs[TILEGX_MAX_INSTRUCTIONS_PER_BUNDLE];
-  int reverse_frame_valid, prolog_done, branch_seen;
+  int reverse_frame_valid, prolog_done, branch_seen, lr_saved_on_stack_p;
   LONGEST prev_sp_value;
   int i, j;
 
@@ -421,6 +421,7 @@ tilegx_analyze_prologue (struct gdbarch* gdbarch,
   prolog_done = 0;
   branch_seen = 0;
   prev_sp_value = 0;
+  lr_saved_on_stack_p = 0;
 
   /* To cut down on round-trip overhead, we fetch multiple bundles
      at once.  These variables describe the range of memory we have
@@ -484,6 +485,12 @@ tilegx_analyze_prologue (struct gdbarch* gdbarch,
 		     See trad-frame.h.  */
 		  cache->saved_regs[saved_register].realreg = saved_register;
 		  cache->saved_regs[saved_register].addr = saved_address;
+		} 
+	      else if (cache
+		       && (operands[0] == TILEGX_SP_REGNUM) 
+		       && (operands[1] == TILEGX_LR_REGNUM))
+		{
+		  lr_saved_on_stack_p = 1;
 		}
 	      break;
 	    case TILEGX_OPC_ADDI:
@@ -737,6 +744,13 @@ tilegx_analyze_prologue (struct gdbarch* gdbarch,
 	}
     }
 
+  if (lr_saved_on_stack_p)
+    {
+      cache->saved_regs[TILEGX_LR_REGNUM].realreg = TILEGX_LR_REGNUM;
+      cache->saved_regs[TILEGX_LR_REGNUM].addr =
+	cache->saved_regs[TILEGX_SP_REGNUM].addr;
+    }
+
   return prolog_end;
 }
 
@@ -821,11 +835,12 @@ tilegx_frame_cache (struct frame_info *this_frame, void **this_cache)
   cache->base = get_frame_register_unsigned (this_frame, TILEGX_SP_REGNUM);
   trad_frame_set_value (cache->saved_regs, TILEGX_SP_REGNUM, cache->base);
 
-  cache->saved_regs[TILEGX_PC_REGNUM] = cache->saved_regs[TILEGX_LR_REGNUM];
   if (cache->start_pc)
     tilegx_analyze_prologue (gdbarch, cache->start_pc, current_pc,
 			     cache, this_frame);
 
+  cache->saved_regs[TILEGX_PC_REGNUM] = cache->saved_regs[TILEGX_LR_REGNUM];
+
   return cache;
 }
 
-- 
1.7.10.3