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perf dwarf-aux: Collect all variable locations for insn tracking

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Previously, only the first DWARF location entry was collected for each
variable. This was based on the assumption that instruction tracking
could reconstruct the remaining state. However, variables may have
different locations across different address ranges, and relying solely
on instruction tracking can miss valid type information.

Change __die_collect_vars_cb() to iterate over all location entries
using dwarf_getlocations() in a loop. This ensures that variables with
multiple location ranges are properly tracked, improving type coverage.

Signed-off-by: Zecheng Li <zli94@ncsu.edu>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
This commit is contained in:
Zecheng Li
2026-03-09 13:55:24 -04:00
committed by Namhyung Kim
parent 4fb7eefe6c
commit a90407a5a8
1 changed files with 29 additions and 29 deletions
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58
tools/perf/util/dwarf-aux.c
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@@ -1645,6 +1645,7 @@ static int __die_collect_vars_cb(Dwarf_Die *die_mem, void *arg)
Dwarf_Op *ops;
size_t nops;
struct die_var_type *vt;
ptrdiff_t off;
if (tag != DW_TAG_variable && tag != DW_TAG_formal_parameter)
return DIE_FIND_CB_SIBLING;
@@ -1652,41 +1653,40 @@ static int __die_collect_vars_cb(Dwarf_Die *die_mem, void *arg)
if (dwarf_attr(die_mem, DW_AT_location, &attr) == NULL)
return DIE_FIND_CB_SIBLING;
/*
* Only collect the first location as it can reconstruct the
* remaining state by following the instructions.
* start = 0 means it covers the whole range.
*/
if (dwarf_getlocations(&attr, 0, &base, &start, &end, &ops, &nops) <= 0)
return DIE_FIND_CB_SIBLING;
if (!check_allowed_ops(ops, nops))
return DIE_FIND_CB_SIBLING;
if (__die_get_real_type(die_mem, &type_die) == NULL)
return DIE_FIND_CB_SIBLING;
vt = malloc(sizeof(*vt));
if (vt == NULL)
return DIE_FIND_CB_END;
/*
* Collect all location entries as variables may have different
* locations across different address ranges.
*/
off = 0;
while ((off = dwarf_getlocations(&attr, off, &base, &start, &end, &ops, &nops)) > 0) {
if (!check_allowed_ops(ops, nops))
continue;
/* Usually a register holds the value of a variable */
vt->is_reg_var_addr = false;
vt = malloc(sizeof(*vt));
if (vt == NULL)
return DIE_FIND_CB_END;
if (((ops->atom >= DW_OP_breg0 && ops->atom <= DW_OP_breg31) ||
ops->atom == DW_OP_bregx || ops->atom == DW_OP_fbreg) &&
!is_breg_access_indirect(ops, nops))
/* The register contains an address of the variable. */
vt->is_reg_var_addr = true;
/* Usually a register holds the value of a variable */
vt->is_reg_var_addr = false;
vt->die_off = dwarf_dieoffset(&type_die);
vt->addr = start;
vt->end = end;
vt->has_range = (end != 0 || start != 0);
vt->reg = reg_from_dwarf_op(ops);
vt->offset = offset_from_dwarf_op(ops);
vt->next = *var_types;
*var_types = vt;
if (((ops->atom >= DW_OP_breg0 && ops->atom <= DW_OP_breg31) ||
ops->atom == DW_OP_bregx || ops->atom == DW_OP_fbreg) &&
!is_breg_access_indirect(ops, nops))
/* The register contains an address of the variable. */
vt->is_reg_var_addr = true;
vt->die_off = dwarf_dieoffset(&type_die);
vt->addr = start;
vt->end = end;
vt->has_range = (end != 0 || start != 0);
vt->reg = reg_from_dwarf_op(ops);
vt->offset = offset_from_dwarf_op(ops);
vt->next = *var_types;
*var_types = vt;
}
return DIE_FIND_CB_SIBLING;
}