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RFC: libunwind-frame.c -vs- optimized-out
- From: Tom Tromey <tromey at redhat dot com>
- To: gdb-patches at sourceware dot org
- Date: Fri, 02 Jul 2010 13:42:36 -0600
- Subject: RFC: libunwind-frame.c -vs- optimized-out
PR 11780 concerns another case where the optimized-out change I made
breaks unwinding. In this case the failures are on IA-64.
ia64_libunwind_frame_prev_register calls libunwind_frame_prev_register
and then uses the contents of the result, for example:
/* Let libunwind do most of the work. */
val = libunwind_frame_prev_register (this_frame, this_cache, reg);
[...]
prN_val = extract_bit_field (value_contents_all (val),
regnum - VP0_REGNUM, 1);
[...]
However, libunwind_frame_prev_register calls set_value_optimized_out on
this value.
I don't really understand why it is doing this. It looks like the code
there is computing something, and strangely it seems though that the
error cases return a not-optimized-out value. E.g., here, unw_get_reg_p
returns a negative value on failure:
ret = unw_get_reg_p (&cache->cursor, uw_regnum, &intval);
if (ret < 0)
return frame_unwind_got_constant (this_frame, regnum, 0);
val = frame_unwind_got_constant (this_frame, regnum, intval);
}
set_value_optimized_out (val, 1);
So, this seems like the logic is possibly backward.
The appended patch fixes the IA-64 regressions. However, I am reluctant
to commit it without understanding what is going on here.
Tom
2010-07-02 Tom Tromey <tromey@redhat.com>
PR exp/11780:
* libunwind-frame.c (libunwind_frame_prev_register): Don't set
value as optimized-out.
Index: libunwind-frame.c
===================================================================
RCS file: /cvs/src/src/gdb/libunwind-frame.c,v
retrieving revision 1.26
diff -u -r1.26 libunwind-frame.c
--- libunwind-frame.c 14 May 2010 23:41:04 -0000 1.26
+++ libunwind-frame.c 2 Jul 2010 19:34:58 -0000
@@ -348,7 +348,6 @@
return frame_unwind_got_constant (this_frame, regnum, 0);
val = frame_unwind_got_constant (this_frame, regnum, intval);
}
- set_value_optimized_out (val, 1);
break;
}
}