gcc/g++ is generating the same DWARF DW_AT_ranges info for two different
functions. This makes translation from a PC address to the function difficult
since a given PC can map to two different functions.
Using the following test file:
// Compile as "g++ -O2 -ggdb --save-temps -o t t.cc"
#include <vector>
using namespace std;
int main ()
{
vector<int> V(10);
V[10] = 1;
}
the DWARF info emitted by gcc assigns a block of addresses to two
different functions, get_allocator and _S_get_pool. Here is an edited
dump of the DWARF info produced by readelf.
<2><2523>: Abbrev Number: 38 (DW_TAG_subprogram)
DW_AT_name : (indirect string, offset: 0x1d35): get_allocator
<1><3807>: Abbrev Number: 77 (DW_TAG_subprogram)
DW_AT_specification: <2523>
DW_AT_inline : 3 (declared as inline and inlined)
<3><39de>: Abbrev Number: 92 (DW_TAG_inlined_subroutine)
DW_AT_abstract_origin: <3807>
DW_AT_ranges : 0x5c8
000005c8 080488c9 080488d0
000005c8 08048a50 08048af6
000005c8 080488dc 080488e2
000005c8 <End of list>
<2><227c>: Abbrev Number: 64 (DW_TAG_subprogram)
DW_AT_name : (indirect string, offset: 0x666): _S_get_pool
<1><2e03>: Abbrev Number: 77 (DW_TAG_subprogram)
DW_AT_specification: <227c>
DW_AT_inline : 3 (declared as inline and inlined)
<6><3a12>: Abbrev Number: 92 (DW_TAG_inlined_subroutine)
DW_AT_abstract_origin: <2e03>
DW_AT_ranges : 0x628
00000628 080488c9 080488d0
00000628 08048a50 08048af6
00000628 080488dc 080488e2
00000628 <End of list>
When one function inlines another, and all of the associated code is generated
for the inlinee with no code generated for the inliner, my reading of the draft
DWARF 3 spec, which describes DW_AT_ranges, would indicate that no
DW_AT_low_pc, DW_AT_high_pc, or DW_AT_ranges attributes should be generated for
the inliner function:
2.16 Code Addresses and Ranges
Any debugging information entry describing an entity that has a
machine code address or range of machine code addresses, which
includes compilation units, module initialization, subroutines,
ordinary blocks, try/catch blocks, labels and the like, may have " A
DW_AT_low_pc attribute for a single address, " A DW_AT_low_pc and
DW_AT_high_pc pair of attributes for a single contiguous range of
addresses, or " A DW_AT_ranges attribute for a non-contiguous range of
addresses. If an entity has no associated machine code, none of these
attributes are specified.
My understanding, perhaps incorrect, is that the entire purpose of using the
DW_AT_ranges attribute, instead of the DW_AT_low_pc/DW_AT_high_pc attributes,
is to be able to accurately describe situations like this, where code from
different functions is interleaved due to optimization. No given address
should appear in more than one DW_AT_ranges entry.
--
Summary: g++ generates same DW_AT_ranges info for two different
functions
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: debug
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: fnf at specifixinc dot com
CC: fnf at specifixinc dot com,gcc-bugs at gcc dot gnu dot
org
GCC build triplet: i686-pc-linux-gnu
GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20967
