[PATCH 01/14] Fix latent bug in dwarf2_find_containing_comp_unit

Tom Tromey
2020-02-15T16:54:51Z

dwarf2_find_containing_comp_unit has this in its binary search:

if (mid_cu->is_dwz > offset_in_dwz
|| (mid_cu->is_dwz == offset_in_dwz
&& mid_cu->sect_off + mid_cu->length >= sect_off))
high = mid;

The intent here is to determine whether SECT_OFF appears in or before
MID_CU.

I believe this has an off-by-one error, and that the check should use
">" rather than ">=". If the two side are equal, then SECT_OFF
actually appears at the start of the next CU.

I've had this patch kicking around for ages but I forget how I found
the problem.

gdb/ChangeLog
2020-02-15 Tom Tromey <tom@tromey.com>

* dwarf2/read.c (dwarf2_find_containing_comp_unit): Use ">", not
">=", in binary search.
---
gdb/ChangeLog | 5 +++++
gdb/dwarf2/read.c | 2 +-
2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index e74383e01dc..e373cc0af2c 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -24171,7 +24171,7 @@ dwarf2_find_containing_comp_unit (sect_offset sect_off,
mid_cu = dwarf2_per_objfile->all_comp_units[mid];
if (mid_cu->is_dwz > offset_in_dwz
|| (mid_cu->is_dwz == offset_in_dwz
- && mid_cu->sect_off + mid_cu->length >= sect_off))
+ && mid_cu->sect_off + mid_cu->length > sect_off))
high = mid;
else
low = mid + 1;
--
2.17.2