Re: [PATCH V7 15/18] tools/perf: Add support to find global register variables using find_data_type_global_reg
From: Namhyung Kim <namhyung@kernel.org>
Date: 2024-07-18 05:11:35
Also in:
linux-perf-users, lkml
Hello, On Sat, Jul 13, 2024 at 10:25:26PM +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 NULLI'm not sure why die_get_real_type() returned NULL. The variable has the type attribute and the function run the loop only if the type is either const, restrict, volatile, shared or typedef. So I think it should return the base_type DIE.
quoted hunk ↗ jump to hunk
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 <redacted> --- tools/perf/util/annotate-data.c | 42 ++++++++++++++++++++++++++++ tools/perf/util/annotate.c | 8 ++++++ tools/perf/util/annotate.h | 1 + tools/perf/util/include/dwarf-regs.h | 1 + 4 files changed, 52 insertions(+)diff --git a/tools/perf/util/annotate-data.c b/tools/perf/util/annotate-data.c index 734acdd8c4b7..a5b4429ede57 100644 --- a/tools/perf/util/annotate-data.c +++ b/tools/perf/util/annotate-data.c@@ -1170,6 +1170,42 @@ 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, *vt = NULL; + + die_collect_vars(cu_die, &vt); + for (var_types = vt; var_types; var_types = var_types->next) { + if (var_types->reg != reg) + continue; + if (dwarf_offdie(dloc->di->dbg, var_types->die_off, &vr_die)) { + if (die_get_real_type(&vr_die, type_die) == NULL) {
Ok, I think I know the reason. You don't need to call die_get_real_type() here as var_types already has the type, not the variable. Usually we want a pointer type for a variable. For the final result, you want the target type of the pointer though.
+ 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",I think it's better to say found by global register %d.
quoted hunk ↗ jump to hunk
+ dwarf_diename(type_die), (long)dwarf_dieoffset(type_die)); + break; + } + } + + delete_var_types(vt); + + 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 +1253,12 @@ 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 ce99db291c5e..8db2f32700aa 100644 --- a/tools/perf/util/annotate.c +++ b/tools/perf/util/annotate.c@@ -2425,6 +2425,14 @@ 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;
Just bool global_reg would be enough unless you plan to add more register types. Thanks, Namhyung
quoted hunk ↗ jump to hunk
}; enum annotated_insn_ops {diff --git a/tools/perf/util/include/dwarf-regs.h b/tools/perf/util/include/dwarf-regs.h index 75b28dcc8317..a5e8e9498683 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