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

Athira Rajeev
2024-06-25T12:45:38Z

> On 25 Jun 2024, at 11:47 AM, Namhyung Kim <namhyung@kernel.org> wrote:
>
> 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.
Ok
>
>> + */
>> +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

Sure, will make these changes in V5

Thanks
Athira
>
>
>> + 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