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

Namhyung Kim
2024-06-25T06:17:02Z

On Fri, Jun 14, 2024 at 10:56:29PM +0530, Athira Rajeev wrote:
> 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.

Ok, if they always point to the same type, you may cache the result and
avoid the repeated search everytime.

> + */
> +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;
> + }

Please add 'delete_var_types(var_types);' here.

Thanks,
Namhyung

> + 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
>