[V4 14/16] tools/perf: Add support to find global register variables using find_data_type_global_reg

Athira Rajeev
2024-06-14T17:27:41Z

There are cases where define a global register variable and associate it
with a specified register. Example, in powerpc, two registers are
defined to represent variable:
1. r13: represents local_paca
register struct paca_struct *local_paca asm("r13");

2. r1: represents stack_pointer
register void *__stack_pointer asm("r1");

These regs are present in dwarf debug as DW_OP_reg as part of variables
in the cu_die (compile unit). These are not present in die search done
in the list of nested scopes since these are global register variables.

Example for local_paca represented by r13:

<<>>
<1><18dc6b4>: Abbrev Number: 128 (DW_TAG_variable)
<18dc6b6> DW_AT_name : (indirect string, offset: 0x3861): local_paca
<18dc6ba> DW_AT_decl_file : 48
<18dc6bb> DW_AT_decl_line : 36
<18dc6bc> DW_AT_decl_column : 30
<18dc6bd> DW_AT_type : <0x18dc6c3>
<18dc6c1> DW_AT_external : 1
<18dc6c1> DW_AT_location : 1 byte block: 5d (DW_OP_reg13 (r13))

<1><18dc6c3>: Abbrev Number: 3 (DW_TAG_pointer_type)
<18dc6c4> DW_AT_byte_size : 8
<18dc6c4> DW_AT_type : <0x18dc353>

Where DW_AT_type : <0x18dc6c3> further points to :

<1><18dc6c3>: Abbrev Number: 3 (DW_TAG_pointer_type)
<18dc6c4> DW_AT_byte_size : 8
<18dc6c4> DW_AT_type : <0x18dc353>

which belongs to:

<1><18dc353>: Abbrev Number: 67 (DW_TAG_structure_type)
<18dc354> DW_AT_name : (indirect string, offset: 0x56cd): paca_struct
<18dc358> DW_AT_byte_size : 2944
<18dc35a> DW_AT_alignment : 128
<18dc35b> DW_AT_decl_file : 48
<18dc35c> DW_AT_decl_line : 61
<18dc35d> DW_AT_decl_column : 8
<18dc35d> DW_AT_sibling : <0x18dc6b4>
<<>>

Similar is case with "r1".

<<>>
<1><18dd772>: Abbrev Number: 129 (DW_TAG_variable)
<18dd774> DW_AT_name : (indirect string, offset: 0x11ba): current_stack_pointer
<18dd778> DW_AT_decl_file : 51
<18dd779> DW_AT_decl_line : 1468
<18dd77b> DW_AT_decl_column : 24
<18dd77c> DW_AT_type : <0x18da5cd>
<18dd780> DW_AT_external : 1
<18dd780> DW_AT_location : 1 byte block: 51 (DW_OP_reg1 (r1))

where 18da5cd is:

<1><18da5cd>: Abbrev Number: 47 (DW_TAG_base_type)
<18da5ce> DW_AT_byte_size : 8
<18da5cf> DW_AT_encoding : 7 (unsigned)
<18da5d0> DW_AT_name : (indirect string, offset: 0x55c7): long unsigned int
<<>>

To identify data type for these two special cases, iterate over
variables in the CU die (Compile Unit) and match it with the register.
If the variable is a base type, ie die_get_real_type will return NULL
here, set offset to zero. With the changes, data type for "paca_struct"
and "long unsigned int" for r1 is identified.

Snippet from ./perf report -s type,type_off

12.85% long unsigned int long unsigned int +0 (no field)
4.68% struct paca_struct struct paca_struct +2312 (__current)
4.57% struct paca_struct struct paca_struct +2354 (irq_soft_mask)

Signed-off-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
---
tools/perf/util/annotate-data.c | 40 ++++++++++++++++++++++++++++
tools/perf/util/annotate.c | 8 ++++++
tools/perf/util/annotate.h | 1 +
tools/perf/util/include/dwarf-regs.h | 1 +
4 files changed, 50 insertions(+)

diff --git a/tools/perf/util/annotate-data.c b/tools/perf/util/annotate-data.c
index 734acdd8c4b7..82232f2d8e16 100644
--- a/tools/perf/util/annotate-data.c
+++ b/tools/perf/util/annotate-data.c
@@ -1170,6 +1170,40 @@ static int find_data_type_block(struct data_loc_info *dloc,
return ret;
}

+/*
+ * Handle cases where define a global register variable and
+ * associate it with a specified register. These regs are
+ * present in dwarf debug as DW_OP_reg as part of variables
+ * in the cu_die (compile unit). Iterate over variables in the
+ * cu_die and match with reg to identify data type die.
+ */
+static int find_data_type_global_reg(struct data_loc_info *dloc, int reg, Dwarf_Die *cu_die,
+ Dwarf_Die *type_die)
+{
+ Dwarf_Die vr_die;
+ int ret = -1;
+ struct die_var_type *var_types = NULL;
+
+ die_collect_vars(cu_die, &var_types);
+ while (var_types) {
+ if (var_types->reg == reg) {
+ if (dwarf_offdie(dloc->di->dbg, var_types->die_off, &vr_die)) {
+ if (die_get_real_type(&vr_die, type_die) == NULL) {
+ dloc->type_offset = 0;
+ dwarf_offdie(dloc->di->dbg, var_types->die_off, type_die);
+ }
+ pr_debug_type_name(type_die, TSR_KIND_TYPE);
+ ret = 0;
+ pr_debug_dtp("found by CU for %s (die:%#lx)\n",
+ dwarf_diename(type_die), (long)dwarf_dieoffset(type_die));
+ }
+ break;
+ }
+ var_types = var_types->next;
+ }
+ return ret;
+}
+
/* The result will be saved in @type_die */
static int find_data_type_die(struct data_loc_info *dloc, Dwarf_Die *type_die)
{
@@ -1217,6 +1251,12 @@ static int find_data_type_die(struct data_loc_info *dloc, Dwarf_Die *type_die)
pr_debug_dtp("CU for %s (die:%#lx)\n",
dwarf_diename(&cu_die), (long)dwarf_dieoffset(&cu_die));

+ if (loc->reg_type == DWARF_REG_GLOBAL) {
+ ret = find_data_type_global_reg(dloc, reg, &cu_die, type_die);
+ if (!ret)
+ goto out;
+ }
+
if (reg == DWARF_REG_PC) {
if (get_global_var_type(&cu_die, dloc, dloc->ip, dloc->var_addr,
&offset, type_die)) {
diff --git a/tools/perf/util/annotate.c b/tools/perf/util/annotate.c
index bfa6420dc4b9..c7e4fd16e8b4 100644
--- a/tools/perf/util/annotate.c
+++ b/tools/perf/util/annotate.c
@@ -2431,6 +2431,14 @@ struct annotated_data_type *hist_entry__get_data_type(struct hist_entry *he)
op_loc->reg1 = DWARF_REG_PC;
}

+ /* Global reg variable 13 and 1
+ * assign to DWARF_REG_GLOBAL
+ */
+ if (arch__is(arch, "powerpc")) {
+ if ((op_loc->reg1 == 13) || (op_loc->reg1 == 1))
+ op_loc->reg_type = DWARF_REG_GLOBAL;
+ }
+
mem_type = find_data_type(&dloc);

if (mem_type == NULL && is_stack_canary(arch, op_loc)) {
diff --git a/tools/perf/util/annotate.h b/tools/perf/util/annotate.h
index 9ba772f46270..ad69842a8ebc 100644
--- a/tools/perf/util/annotate.h
+++ b/tools/perf/util/annotate.h
@@ -475,6 +475,7 @@ struct annotated_op_loc {
bool mem_ref;
bool multi_regs;
bool imm;
+ int reg_type;
};

enum annotated_insn_ops {
diff --git a/tools/perf/util/include/dwarf-regs.h b/tools/perf/util/include/dwarf-regs.h
index 7ea39362ecaf..a873c906a86b 100644
--- a/tools/perf/util/include/dwarf-regs.h
+++ b/tools/perf/util/include/dwarf-regs.h
@@ -5,6 +5,7 @@

#define DWARF_REG_PC 0xd3af9c /* random number */
#define DWARF_REG_FB 0xd3affb /* random number */
+#define DWARF_REG_GLOBAL 0xd3affc /* random number */

#ifdef HAVE_DWARF_SUPPORT
const char *get_arch_regstr(unsigned int n);
--
2.43.0