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Message-ID: <ZpinT_O_13pl-Lab@google.com>
Date: Wed, 17 Jul 2024 22:25:35 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Athira Rajeev <atrajeev@...ux.vnet.ibm.com>
Cc: acme@...nel.org, jolsa@...nel.org, adrian.hunter@...el.com,
irogers@...gle.com, segher@...nel.crashing.org,
christophe.leroy@...roup.eu, linux-kernel@...r.kernel.org,
linux-perf-users@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
akanksha@...ux.ibm.com, maddy@...ux.ibm.com, kjain@...ux.ibm.com,
disgoel@...ux.vnet.ibm.com
Subject: Re: [PATCH V7 16/18] tools/perf: Add support for global_die to
capture name of variable in case of register defined variable
On Sat, Jul 13, 2024 at 10:25:27PM +0530, Athira Rajeev wrote:
> In case of register defined variable (found using
> find_data_type_global_reg), if the type of variable happens to be base
> type (example, long unsigned int), perf report captures it as:
>
> 12.85% long unsigned int long unsigned int +0 (no field)
>
> The above data type is actually referring to samples captured while
> accessing "r1" which represents current stack pointer in powerpc.
> register void *__stack_pointer asm("r1");
>
> The dwarf debug contains this as:
>
> <<>>
> <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
> <<>>
Actually this is different from your description. I expect
DW_TAG_variable
DW_AT_name: __stack_pointer
DW_AT_type: <pointer_type> (void *)
But it seems your DWARF has
DW_TAG_variable
DW_AT_name: current_stack_pointer
DW_AT_type: <base_type> (long unsigned int)
>
> To make it more clear to the user, capture the DW_AT_name of the
> variable and save it as part of Dwarf_Global. Dwarf_Global is used so
> that it can be used and retrieved while presenting the result.
>
> Update "dso__findnew_data_type" function to set "var_name" if
> variable name is set as part of Dwarf_Global.
>
> Signed-off-by: Athira Rajeev <atrajeev@...ux.vnet.ibm.com>
> ---
> tools/perf/util/annotate-data.c | 30 ++++++++++++++++++++++++------
> tools/perf/util/dwarf-aux.c | 1 +
> tools/perf/util/dwarf-aux.h | 1 +
> 3 files changed, 26 insertions(+), 6 deletions(-)
>
> diff --git a/tools/perf/util/annotate-data.c b/tools/perf/util/annotate-data.c
> index a5b4429ede57..8d05f3dbddf6 100644
> --- a/tools/perf/util/annotate-data.c
> +++ b/tools/perf/util/annotate-data.c
> @@ -268,28 +268,37 @@ static void delete_members(struct annotated_member *member)
> }
>
> static struct annotated_data_type *dso__findnew_data_type(struct dso *dso,
> - Dwarf_Die *type_die)
> + Dwarf_Die *type_die, Dwarf_Global *global_die)
> {
> struct annotated_data_type *result = NULL;
> struct annotated_data_type key;
> struct rb_node *node;
> struct strbuf sb;
> + struct strbuf sb_var_name;
> char *type_name;
> + char *var_name = NULL;
> Dwarf_Word size;
>
> strbuf_init(&sb, 32);
> + strbuf_init(&sb_var_name, 32);
> if (die_get_typename_from_type(type_die, &sb) < 0)
> strbuf_add(&sb, "(unknown type)", 14);
> + if (global_die->name) {
> + strbuf_addstr(&sb_var_name, global_die->name);
> + var_name = strbuf_detach(&sb_var_name, NULL);
I think you can just use strdup(global_die->name).
> + }
> type_name = strbuf_detach(&sb, NULL);
> dwarf_aggregate_size(type_die, &size);
>
> /* Check existing nodes in dso->data_types tree */
> key.self.type_name = type_name;
> + key.self.var_name = var_name;
> key.self.size = size;
> node = rb_find(&key, dso__data_types(dso), data_type_cmp);
> if (node) {
> result = rb_entry(node, struct annotated_data_type, node);
> free(type_name);
> + free(var_name);
> return result;
> }
>
> @@ -297,10 +306,12 @@ static struct annotated_data_type *dso__findnew_data_type(struct dso *dso,
> result = zalloc(sizeof(*result));
> if (result == NULL) {
> free(type_name);
> + free(var_name);
> return NULL;
> }
>
> result->self.type_name = type_name;
> + result->self.var_name = var_name;
> result->self.size = size;
> INIT_LIST_HEAD(&result->self.children);
>
> @@ -1178,7 +1189,7 @@ static int find_data_type_block(struct data_loc_info *dloc,
> * 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 *type_die, Dwarf_Global *global_die)
> {
> Dwarf_Die vr_die;
> int ret = -1;
> @@ -1191,8 +1202,11 @@ static int find_data_type_global_reg(struct data_loc_info *dloc, int reg, Dwarf_
> 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;
> + global_die->name = var_types->name;
> dwarf_offdie(dloc->di->dbg, var_types->die_off, type_die);
> }
> + global_die->die_offset = (long)dwarf_dieoffset(type_die);
> + global_die->cu_offset = (long)dwarf_dieoffset(cu_die);
It seems all you need is the name of the variable. Can we simply pass
the name instead of Dwarf_Global?
> pr_debug_type_name(type_die, TSR_KIND_TYPE);
> ret = 0;
> pr_debug_dtp("found by CU for %s (die:%#lx)\n",
> @@ -1207,7 +1221,8 @@ static int find_data_type_global_reg(struct data_loc_info *dloc, int reg, Dwarf_
> }
>
> /* The result will be saved in @type_die */
> -static int find_data_type_die(struct data_loc_info *dloc, Dwarf_Die *type_die)
> +static int find_data_type_die(struct data_loc_info *dloc, Dwarf_Die *type_die,
> + Dwarf_Global *global_die)
> {
> struct annotated_op_loc *loc = dloc->op;
> Dwarf_Die cu_die, var_die;
> @@ -1221,6 +1236,8 @@ static int find_data_type_die(struct data_loc_info *dloc, Dwarf_Die *type_die)
> u64 pc;
> char buf[64];
>
> + memset(global_die, 0, sizeof(Dwarf_Global));
> +
> if (dloc->op->multi_regs)
> snprintf(buf, sizeof(buf), "reg%d, reg%d", dloc->op->reg1, dloc->op->reg2);
> else if (dloc->op->reg1 == DWARF_REG_PC)
> @@ -1254,7 +1271,7 @@ static int find_data_type_die(struct data_loc_info *dloc, Dwarf_Die *type_die)
> 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);
> + ret = find_data_type_global_reg(dloc, reg, &cu_die, type_die, global_die);
> if (!ret)
> goto out;
> }
> @@ -1390,6 +1407,7 @@ struct annotated_data_type *find_data_type(struct data_loc_info *dloc)
> struct annotated_data_type *result = NULL;
> struct dso *dso = map__dso(dloc->ms->map);
> Dwarf_Die type_die;
> + Dwarf_Global global_die;
>
> dloc->di = debuginfo__new(dso__long_name(dso));
> if (dloc->di == NULL) {
> @@ -1405,10 +1423,10 @@ struct annotated_data_type *find_data_type(struct data_loc_info *dloc)
>
> dloc->fbreg = -1;
>
> - if (find_data_type_die(dloc, &type_die) < 0)
> + if (find_data_type_die(dloc, &type_die, &global_die) < 0)
> goto out;
>
> - result = dso__findnew_data_type(dso, &type_die);
> + result = dso__findnew_data_type(dso, &type_die, &global_die);
>
> out:
> debuginfo__delete(dloc->di);
> diff --git a/tools/perf/util/dwarf-aux.c b/tools/perf/util/dwarf-aux.c
> index 44ef968a7ad3..9e61ff326651 100644
> --- a/tools/perf/util/dwarf-aux.c
> +++ b/tools/perf/util/dwarf-aux.c
> @@ -1610,6 +1610,7 @@ static int __die_collect_vars_cb(Dwarf_Die *die_mem, void *arg)
> vt->reg = reg_from_dwarf_op(ops);
> vt->offset = offset_from_dwarf_op(ops);
> vt->next = *var_types;
> + vt->name = dwarf_diename(die_mem);
Hmm.. maybe we can just collect variables (not their types) directly,
then we can get the name from the variable DIE without saving it in
the struct die_var_type.
Thanks,
Namhyung
> *var_types = vt;
>
> return DIE_FIND_CB_SIBLING;
> diff --git a/tools/perf/util/dwarf-aux.h b/tools/perf/util/dwarf-aux.h
> index 24446412b869..406a5b1e269b 100644
> --- a/tools/perf/util/dwarf-aux.h
> +++ b/tools/perf/util/dwarf-aux.h
> @@ -146,6 +146,7 @@ struct die_var_type {
> u64 addr;
> int reg;
> int offset;
> + const char *name;
> };
>
> /* Return type info of a member at offset */
> --
> 2.43.0
>
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