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

Daniel Jacobowitz
2004-03-22T21:07:22Z

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;