https://sourceware.org/bugzilla/show_bug.cgi?id=28294
Bug ID: 28294
Summary: dwarf_aggregate_size fails on some array types
Product: elfutils
Version: unspecified
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: libdw
Assignee: unassigned at sourceware dot org
Reporter: egb.atos at gmail dot com
CC: elfutils-devel at sourceware dot org
Target Milestone: ---
In dwarf_aggregate_size.c, the helper function array_size unconditionally uses
dwarf_formsdata to obtain the value of the DW_AT_upper_bound attribute for
array types. In many cases, this will return a negative value for C arrays
that have positive upper bounds, causing the function to return a failure
value, which propagates up through dwarf_aggregate_size.
This is an exemplary type (via readelf -w):
<1><90e>: Abbrev Number: 37 (DW_TAG_array_type)
<90f> DW_AT_type : <0x118>
<2><913>: Abbrev Number: 11 (DW_TAG_subrange_type)
<914> DW_AT_type : <0x2c>
<918> DW_AT_upper_bound : 249
And the same type, via eu-readelf --debug-dump=info:
[ 90e] array_type abbrev: 37
type (ref4) [ 118]
[ 913] subrange_type abbrev: 11
type (ref4) [ 2c]
upper_bound (data1) 249
If dwarf_aggregate_size is called on this type, when it gets the upper_bound
attribute, it will get a value of -7, and fail. For other array sizes, this
will work.
Looking around a bit, the closest discussion I could find on the topic was this
one about signed vs unsigned interpretation of array bounds back in 2005:
http://www.dwarfstd.org/ShowIssue.php?issue=020702.1
I exchanged emails with Mark Wielaard on this, and he indicated that this did
appear to be a bug, but he wasn't sure yet where the correct fix would be.
I've tried this with a RISCV compiler (version 8.3.0), an ARM compiler (version
7.3.1) and an x86 gcc (version 7.5.0). I've not tried it with later versions.
Here's the sample code I compiled to get the output above. The output in the
report is from the ARM compiler.
#include <string.h>
int foofunc(int v, char *s) {
char buff[250];
strcpy(buff, s);
return buff[v];
}
int main() {
return foofunc(4, "fdjkfd");
}
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