Re: [rfa/mips] Stop backtraces when we've lost the PC

[Daniel Jacobowitz <drow@false.org>]

On Wed, Mar 17, 2004 at 03:07:02PM -0500, Andrew Cagney wrote:
> Other than that, just an observation that the binary search is [already] 
> pretty messed up.  In all likelyhood the test:
> 
> 	if (pdr_pc == pc)
> 
> will never fire and having it gains little if anything (one less 
> iteration VS logN extra compares).  Eliminating it means cleaning up the 
> binary search though.   Can you attach a fixme to that test indicating 
> that it should be eliminated.

It's pretty easy to clean up the binary search instead, so I did that.

> I also suspect that STARTADDR's computation can be delayed until it is 
> needed (the latter reference that goes with the "pathological", should 
> no longer occure, I think it has been moved into symbol reading. 
> However, leave that for the moment.

I'm pretty sure I tried that, and it meant we stopped using the partial
symbol table to find the beginnings of functions in some cases, leading
to loud failures from heuristic_proc_start.  startaddr is returned via
*addrptr to the caller.

> Otherwize ok, and way better than the original patch, thanks,

Thanks.  Here's what I'll checked in after rerunning some tests.

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer

2004-03-22  Daniel Jacobowitz  <drow@mvista.com>

	* mips-tdep.c (non_heuristic_proc_desc): Search using the specified
	PC rather than the partial function start address.  Use the start
	address to sanity check the found PDR.

Index: mips-tdep.c
===================================================================
RCS file: /big/fsf/rsync/src-cvs/src/gdb/mips-tdep.c,v
retrieving revision 1.283
diff -u -p -r1.283 mips-tdep.c
--- mips-tdep.c	17 Feb 2004 15:21:21 -0000	1.283
+++ mips-tdep.c	22 Mar 2004 20:35:32 -0000
@@ -2352,38 +2352,70 @@ non_heuristic_proc_desc (CORE_ADDR pc, C
 	{
 	  int low, mid, high;
 	  char *ptr;
+	  CORE_ADDR pdr_pc;
 
 	  low = 0;
 	  high = priv->size / 32;
 
+	  /* We've found a .pdr section describing this objfile.  We want to
+	     find the entry which describes this code address.  The .pdr
+	     information is not very descriptive; we have only a function
+	     start address.  We have to look for the closest entry, because
+	     the local symbol at the beginning of this function may have
+	     been stripped - so if we ask the symbol table for the start
+	     address we may get a preceding global function.  */
+
+	  /* First, find the last .pdr entry starting at or before PC.  */
 	  do
 	    {
-	      CORE_ADDR pdr_pc;
-
 	      mid = (low + high) / 2;
 
 	      ptr = priv->contents + mid * 32;
 	      pdr_pc = bfd_get_signed_32 (sec->objfile->obfd, ptr);
 	      pdr_pc += ANOFFSET (sec->objfile->section_offsets,
 				  SECT_OFF_TEXT (sec->objfile));
-	      if (pdr_pc == startaddr)
-		break;
-	      if (pdr_pc > startaddr)
+
+	      if (pdr_pc > pc)
 		high = mid;
 	      else
 		low = mid + 1;
 	    }
 	  while (low != high);
 
-	  if (low != high)
+	  /* Both low and high point one past the PDR of interest.  If
+	     both are zero, that means this PC is before any region
+	     covered by a PDR, i.e. pdr_pc for the first PDR entry is
+	     greater than PC.  */
+	  if (low > 0)
+	    {
+	      ptr = priv->contents + (low - 1) * 32;
+	      pdr_pc = bfd_get_signed_32 (sec->objfile->obfd, ptr);
+	      pdr_pc += ANOFFSET (sec->objfile->section_offsets,
+				  SECT_OFF_TEXT (sec->objfile));
+	    }
+
+	  /* We don't have a range, so we have no way to know for sure
+	     whether we're in the correct PDR or a PDR for a preceding
+	     function and the current function was a stripped local
+	     symbol.  But if the PDR's PC is at least as great as the
+	     best guess from the symbol table, assume that it does cover
+	     the right area; if a .pdr section is present at all then
+	     nearly every function will have an entry.  The biggest exception
+	     will be the dynamic linker stubs; conveniently these are
+	     placed before .text instead of after.  */
+
+	  if (pc >= pdr_pc && pdr_pc >= startaddr)
 	    {
 	      struct symbol *sym = find_pc_function (pc);
 
+	      if (addrptr)
+		*addrptr = pdr_pc;
+
 	      /* Fill in what we need of the proc_desc.  */
 	      proc_desc = (mips_extra_func_info_t)
 		obstack_alloc (&sec->objfile->objfile_obstack,
 			       sizeof (struct mips_extra_func_info));
-	      PROC_LOW_ADDR (proc_desc) = startaddr;
+	      PROC_LOW_ADDR (proc_desc) = pdr_pc;
 
 	      /* Only used for dummy frames.  */
 	      PROC_HIGH_ADDR (proc_desc) = 0;