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dwarf-reader: Workaround libdw dwarf_location_expression bug

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elfutils libdw before 0.184 would not correctly handle a
DW_AT_data_member_location when encoded as a DW_FORM_implicit const
in dwarf_location_expression.

Work around this by first trying to read a data_member_location as a
constant value and only try to get it as a DWARF expression if that

	* src/abg-dwarf-reader.cc (die_constant_data_member_location):
	New function.
	(die_member_offset): Use die_constant_data_member_location
	before calling die_location_expr and eval_quickly.

Signed-off-by: Mark Wielaard <mark@klomp.org>
This commit is contained in:
Mark Wielaard 2021-12-15 17:00:21 +01:00 committed by Dodji Seketeli
parent f76484cc9d
commit 21e0280a8d
1 changed files with 57 additions and 13 deletions
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70
src/abg-dwarf-reader.cc
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@ -8693,6 +8693,37 @@ read_and_convert_DW_at_bit_offset(const Dwarf_Die* die,
return true;
}
/// Get the value of the DW_AT_data_member_location of the given DIE
/// attribute as an constant.
///
/// @param die the DIE to read the attribute from.
///
/// @param offset the attribute as a constant value. This is set iff
/// the function returns true.
///
/// @return true if the attribute exists and has a constant value. In
/// that case the offset is set to the value.
static bool
die_constant_data_member_location(const Dwarf_Die *die,
int64_t& offset)
{
if (!die)
return false;
Dwarf_Attribute attr;
if (!dwarf_attr(const_cast<Dwarf_Die*>(die),
DW_AT_data_member_location,
&attr))
return false;
Dwarf_Word val;
if (dwarf_formudata(&attr, &val) != 0)
return false;
offset = val;
return true;
}
/// Get the offset of a struct/class member as represented by the
/// value of the DW_AT_data_member_location attribute.
///
@ -8758,21 +8789,34 @@ die_member_offset(const read_context& ctxt,
return true;
}
// Otherwise, let's see if the DW_AT_data_member_location attribute and,
// optionally, the DW_AT_bit_offset attributes are present.
if (!die_location_expr(die, DW_AT_data_member_location, &expr, &expr_len))
return false;
// The DW_AT_data_member_location attribute is present.
// Let's evaluate it and get its constant
// sub-expression and return that one.
if (!eval_quickly(expr, expr_len, offset))
// First try to read DW_AT_data_member_location as a plain constant.
// We do this because the generic method using die_location_expr
// might hit a bug in elfutils libdw dwarf_location_expression only
// fixed in elfutils 0.184+. The bug only triggers if the attribute
// is expressed as a (DWARF 5) DW_FORM_implicit_constant. But we
// handle all constants here because that is more consistent (and
// slightly faster in the general case where the attribute isn't a
// full DWARF expression).
if (!die_constant_data_member_location(die, offset))
{
bool is_tls_address = false;
if (!eval_last_constant_dwarf_sub_expr(expr, expr_len,
offset, is_tls_address,
ctxt.dwarf_expr_eval_ctxt()))
// Otherwise, let's see if the DW_AT_data_member_location
// attribute and, optionally, the DW_AT_bit_offset attributes
// are present.
if (!die_location_expr(die, DW_AT_data_member_location,
&expr, &expr_len))
return false;
// The DW_AT_data_member_location attribute is present. Let's
// evaluate it and get its constant sub-expression and return
// that one.
if (!eval_quickly(expr, expr_len, offset))
{
bool is_tls_address = false;
if (!eval_last_constant_dwarf_sub_expr(expr, expr_len,
offset, is_tls_address,
ctxt.dwarf_expr_eval_ctxt()))
return false;
}
}
offset *= 8;