[PATCH 19/23] perf annotate-data: Support general per-cpu access

From: Namhyung Kim
Date: Tue Mar 19 2024 - 01:56:03 EST

This is to support per-cpu variable access often without a matching
DWARF entry. For some reason, I cannot find debug info of per-cpu
variables sometimes. They have more complex pattern to calculate the
address of per-cpu variables like below.

2b7d: mov -0x1e0(%rbp),%rax ; rax = cpu
2b84: mov -0x7da0f7e0(,%rax,8),%rcx ; rcx = __per_cpu_offset[cpu]
* 2b8c: mov 0x34870(%rcx),%rax ; *(__per_cpu_offset[cpu] + 0x34870)

Let's assume the rax register has a number for a CPU at 2b7d. The next
instruction is to get the per-cpu offset' for that cpu. The offset
-0x7da0f7e0 is 0xffffffff825f0820 in u64 which is the address of the
'__per_cpu_offset' array in my system. So it'd get the actual offset
of that CPU's per-cpu region and save it to the rcx register.

Then, at 2b8c, accesses using rcx can be handled same as the global
variable access. To handle this case, it should check if the offset
of the instruction matches to the address of '__per_cpu_offset'.

Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
---
tools/perf/util/annotate-data.c | 213 +++++++++++++++++++++++++-------
1 file changed, 169 insertions(+), 44 deletions(-)

diff --git a/tools/perf/util/annotate-data.c b/tools/perf/util/annotate-data.c
index 48fea0c716ef..83b5aa00f01c 100644
--- a/tools/perf/util/annotate-data.c
+++ b/tools/perf/util/annotate-data.c
@@ -24,6 +24,12 @@
#include "symbol_conf.h"
#include "thread.h"

+enum type_state_kind {
+ TSR_KIND_INVALID = 0,
+ TSR_KIND_TYPE,
+ TSR_KIND_PERCPU_BASE,
+};
+
#define pr_debug_dtp(fmt, ...) \
do { \
if (debug_type_profile) \
@@ -32,7 +38,7 @@ do { \
pr_debug3(fmt, ##__VA_ARGS__); \
} while (0)

-static void pr_debug_type_name(Dwarf_Die *die)
+static void pr_debug_type_name(Dwarf_Die *die, enum type_state_kind kind)
{
struct strbuf sb;
char *str;
@@ -40,6 +46,18 @@ static void pr_debug_type_name(Dwarf_Die *die)
if (!debug_type_profile && verbose < 3)
return;

+ switch (kind) {
+ case TSR_KIND_INVALID:
+ pr_info("\n");
+ return;
+ case TSR_KIND_PERCPU_BASE:
+ pr_info(" percpu base\n");
+ return;
+ case TSR_KIND_TYPE:
+ default:
+ break;
+ }
+
strbuf_init(&sb, 32);
die_get_typename_from_type(die, &sb);
str = strbuf_detach(&sb, NULL);
@@ -53,8 +71,10 @@ static void pr_debug_type_name(Dwarf_Die *die)
*/
struct type_state_reg {
Dwarf_Die type;
+ u32 imm_value;
bool ok;
bool caller_saved;
+ u8 kind;
};

/* Type information in a stack location, dynamically allocated */
@@ -64,6 +84,7 @@ struct type_state_stack {
int offset;
int size;
bool compound;
+ u8 kind;
};

/* FIXME: This should be arch-dependent */
@@ -82,6 +103,8 @@ struct type_state {
struct list_head stack_vars;
/* return value register */
int ret_reg;
+ /* stack pointer register */
+ int stack_reg;
};

static bool has_reg_type(struct type_state *state, int reg)
@@ -105,6 +128,7 @@ static void init_type_state(struct type_state *state, struct arch *arch)
state->regs[10].caller_saved = true;
state->regs[11].caller_saved = true;
state->ret_reg = 0;
+ state->stack_reg = 7;
}
}

@@ -350,7 +374,7 @@ static struct type_state_stack *find_stack_state(struct type_state *state,
return NULL;
}

-static void set_stack_state(struct type_state_stack *stack, int offset,
+static void set_stack_state(struct type_state_stack *stack, int offset, u8 kind,
Dwarf_Die *type_die)
{
int tag;
@@ -364,6 +388,7 @@ static void set_stack_state(struct type_state_stack *stack, int offset,
stack->type = *type_die;
stack->size = size;
stack->offset = offset;
+ stack->kind = kind;

switch (tag) {
case DW_TAG_structure_type:
@@ -377,34 +402,60 @@ static void set_stack_state(struct type_state_stack *stack, int offset,
}

static struct type_state_stack *findnew_stack_state(struct type_state *state,
- int offset, Dwarf_Die *type_die)
+ int offset, u8 kind,
+ Dwarf_Die *type_die)
{
struct type_state_stack *stack = find_stack_state(state, offset);

if (stack) {
- set_stack_state(stack, offset, type_die);
+ set_stack_state(stack, offset, kind, type_die);
return stack;
}

stack = malloc(sizeof(*stack));
if (stack) {
- set_stack_state(stack, offset, type_die);
+ set_stack_state(stack, offset, kind, type_die);
list_add(&stack->list, &state->stack_vars);
}
return stack;
}

+static bool get_global_var_info(struct data_loc_info *dloc, u64 addr,
+ const char **var_name, int *var_offset)
+{
+ struct addr_location al;
+ struct symbol *sym;
+ u64 mem_addr;
+
+ /* Kernel symbols might be relocated */
+ mem_addr = addr + map__reloc(dloc->ms->map);
+
+ addr_location__init(&al);
+ sym = thread__find_symbol_fb(dloc->thread, dloc->cpumode,
+ mem_addr, &al);
+ if (sym) {
+ *var_name = sym->name;
+ /* Calculate type offset from the start of variable */
+ *var_offset = mem_addr - map__unmap_ip(al.map, sym->start);
+ } else {
+ *var_name = NULL;
+ }
+ addr_location__exit(&al);
+ if (*var_name == NULL)
+ return false;
+
+ return true;
+}
+
static bool get_global_var_type(Dwarf_Die *cu_die, struct data_loc_info *dloc,
u64 ip, u64 var_addr, int *var_offset,
Dwarf_Die *type_die)
{
- u64 pc, mem_addr;
+ u64 pc;
int offset;
bool is_pointer = false;
- const char *var_name = NULL;
+ const char *var_name;
Dwarf_Die var_die;
- struct addr_location al;
- struct symbol *sym;

/* Try to get the variable by address first */
if (die_find_variable_by_addr(cu_die, var_addr, &var_die, &offset) &&
@@ -413,19 +464,7 @@ static bool get_global_var_type(Dwarf_Die *cu_die, struct data_loc_info *dloc,
return true;
}

- /* Kernel symbols might be relocated */
- mem_addr = var_addr + map__reloc(dloc->ms->map);
-
- addr_location__init(&al);
- sym = thread__find_symbol_fb(dloc->thread, dloc->cpumode,
- mem_addr, &al);
- if (sym) {
- var_name = sym->name;
- /* Calculate type offset from the start of variable */
- *var_offset = mem_addr - map__unmap_ip(al.map, sym->start);
- }
- addr_location__exit(&al);
- if (var_name == NULL)
+ if (!get_global_var_info(dloc, var_addr, &var_name, var_offset))
return false;

pc = map__rip_2objdump(dloc->ms->map, ip);
@@ -470,27 +509,30 @@ static void update_var_state(struct type_state *state, struct data_loc_info *dlo
continue;

if (var->reg == DWARF_REG_FB) {
- findnew_stack_state(state, var->offset, &mem_die);
+ findnew_stack_state(state, var->offset, TSR_KIND_TYPE,
+ &mem_die);

pr_debug_dtp("var [%"PRIx64"] -%#x(stack)",
insn_offset, -var->offset);
- pr_debug_type_name(&mem_die);
+ pr_debug_type_name(&mem_die, TSR_KIND_TYPE);
} else if (var->reg == fbreg) {
- findnew_stack_state(state, var->offset - fb_offset, &mem_die);
+ findnew_stack_state(state, var->offset - fb_offset,
+ TSR_KIND_TYPE, &mem_die);

pr_debug_dtp("var [%"PRIx64"] -%#x(stack)",
insn_offset, -var->offset + fb_offset);
- pr_debug_type_name(&mem_die);
+ pr_debug_type_name(&mem_die, TSR_KIND_TYPE);
} else if (has_reg_type(state, var->reg) && var->offset == 0) {
struct type_state_reg *reg;

reg = &state->regs[var->reg];
reg->type = mem_die;
+ reg->kind = TSR_KIND_TYPE;
reg->ok = true;

pr_debug_dtp("var [%"PRIx64"] reg%d",
insn_offset, var->reg);
- pr_debug_type_name(&mem_die);
+ pr_debug_type_name(&mem_die, TSR_KIND_TYPE);
}
}
}
@@ -533,11 +575,12 @@ static void update_insn_state_x86(struct type_state *state,
if (die_find_func_rettype(cu_die, func->name, &type_die)) {
tsr = &state->regs[state->ret_reg];
tsr->type = type_die;
+ tsr->kind = TSR_KIND_TYPE;
tsr->ok = true;

pr_debug_dtp("call [%x] return -> reg%d",
insn_offset, state->ret_reg);
- pr_debug_type_name(&type_die);
+ pr_debug_type_name(&type_die, tsr->kind);
}
return;
}
@@ -580,11 +623,12 @@ static void update_insn_state_x86(struct type_state *state,
}

tsr->type = type_die;
+ tsr->kind = TSR_KIND_TYPE;
tsr->ok = true;

pr_debug_dtp("mov [%x] this-cpu addr=%#"PRIx64" -> reg%d",
insn_offset, var_addr, dst->reg1);
- pr_debug_type_name(&tsr->type);
+ pr_debug_type_name(&tsr->type, tsr->kind);
return;
}

@@ -595,11 +639,12 @@ static void update_insn_state_x86(struct type_state *state,
}

tsr->type = state->regs[src->reg1].type;
+ tsr->kind = state->regs[src->reg1].kind;
tsr->ok = true;

pr_debug_dtp("mov [%x] reg%d -> reg%d",
insn_offset, src->reg1, dst->reg1);
- pr_debug_type_name(&tsr->type);
+ pr_debug_type_name(&tsr->type, tsr->kind);
}
/* Case 2. memory to register transers */
if (src->mem_ref && !dst->mem_ref) {
@@ -622,11 +667,13 @@ static void update_insn_state_x86(struct type_state *state,
return;
} else if (!stack->compound) {
tsr->type = stack->type;
+ tsr->kind = stack->kind;
tsr->ok = true;
} else if (die_get_member_type(&stack->type,
offset - stack->offset,
&type_die)) {
tsr->type = type_die;
+ tsr->kind = TSR_KIND_TYPE;
tsr->ok = true;
} else {
tsr->ok = false;
@@ -635,18 +682,20 @@ static void update_insn_state_x86(struct type_state *state,

pr_debug_dtp("mov [%x] -%#x(stack) -> reg%d",
insn_offset, -offset, dst->reg1);
- pr_debug_type_name(&tsr->type);
+ pr_debug_type_name(&tsr->type, tsr->kind);
}
/* And then dereference the pointer if it has one */
else if (has_reg_type(state, sreg) && state->regs[sreg].ok &&
+ state->regs[sreg].kind == TSR_KIND_TYPE &&
die_deref_ptr_type(&state->regs[sreg].type,
src->offset, &type_die)) {
tsr->type = type_die;
+ tsr->kind = TSR_KIND_TYPE;
tsr->ok = true;

pr_debug_dtp("mov [%x] %#x(reg%d) -> reg%d",
insn_offset, src->offset, sreg, dst->reg1);
- pr_debug_type_name(&tsr->type);
+ pr_debug_type_name(&tsr->type, tsr->kind);
}
/* Or check if it's a global variable */
else if (sreg == DWARF_REG_PC) {
@@ -665,11 +714,37 @@ static void update_insn_state_x86(struct type_state *state,
}

tsr->type = type_die;
+ tsr->kind = TSR_KIND_TYPE;
tsr->ok = true;

pr_debug_dtp("mov [%x] global addr=%"PRIx64" -> reg%d",
insn_offset, addr, dst->reg1);
- pr_debug_type_name(&type_die);
+ pr_debug_type_name(&type_die, tsr->kind);
+ }
+ /* And check percpu access with base register */
+ else if (has_reg_type(state, sreg) &&
+ state->regs[sreg].kind == TSR_KIND_PERCPU_BASE) {
+ u64 ip = dloc->ms->sym->start + dl->al.offset;
+ int offset;
+
+ /*
+ * In kernel, %gs points to a per-cpu region for the
+ * current CPU. Access with a constant offset should
+ * be treated as a global variable access.
+ */
+ if (get_global_var_type(cu_die, dloc, ip, src->offset,
+ &offset, &type_die) &&
+ die_get_member_type(&type_die, offset, &type_die)) {
+ tsr->type = type_die;
+ tsr->kind = TSR_KIND_TYPE;
+ tsr->ok = true;
+
+ pr_debug_dtp("mov [%x] percpu %#x(reg%d) -> reg%d type=",
+ insn_offset, src->offset, sreg, dst->reg1);
+ pr_debug_type_name(&tsr->type, tsr->kind);
+ } else {
+ tsr->ok = false;
+ }
}
/* Or try another register if any */
else if (src->multi_regs && sreg == src->reg1 &&
@@ -677,8 +752,22 @@ static void update_insn_state_x86(struct type_state *state,
sreg = src->reg2;
goto retry;
}
- /* It failed to get a type info, mark it as invalid */
else {
+ int offset;
+ const char *var_name = NULL;
+
+ /* it might be per-cpu variable (in kernel) access */
+ if (src->offset < 0) {
+ if (get_global_var_info(dloc, (s64)src->offset,
+ &var_name, &offset) &&
+ !strcmp(var_name, "__per_cpu_offset")) {
+ tsr->kind = TSR_KIND_PERCPU_BASE;
+
+ pr_debug_dtp("mov [%x] percpu base reg%d\n",
+ insn_offset, dst->reg1);
+ }
+ }
+
tsr->ok = false;
}
}
@@ -693,6 +782,8 @@ static void update_insn_state_x86(struct type_state *state,
struct type_state_stack *stack;
int offset = dst->offset - fboff;

+ tsr = &state->regs[src->reg1];
+
stack = find_stack_state(state, offset);
if (stack) {
/*
@@ -703,16 +794,16 @@ static void update_insn_state_x86(struct type_state *state,
* die_get_member_type().
*/
if (!stack->compound)
- set_stack_state(stack, offset,
- &state->regs[src->reg1].type);
+ set_stack_state(stack, offset, tsr->kind,
+ &tsr->type);
} else {
- findnew_stack_state(state, offset,
- &state->regs[src->reg1].type);
+ findnew_stack_state(state, offset, tsr->kind,
+ &tsr->type);
}

pr_debug_dtp("mov [%x] reg%d -> -%#x(stack)",
insn_offset, src->reg1, -offset);
- pr_debug_type_name(&state->regs[src->reg1].type);
+ pr_debug_type_name(&tsr->type, tsr->kind);
}
/*
* Ignore other transfers since it'd set a value in a struct
@@ -824,10 +915,11 @@ static bool check_matching_type(struct type_state *state,
Dwarf_Word size;
u32 insn_offset = dloc->ip - dloc->ms->sym->start;

- pr_debug_dtp("chk [%x] reg%d offset=%#x ok=%d",
- insn_offset, reg, dloc->op->offset, state->regs[reg].ok);
+ pr_debug_dtp("chk [%x] reg%d offset=%#x ok=%d kind=%d",
+ insn_offset, reg, dloc->op->offset,
+ state->regs[reg].ok, state->regs[reg].kind);

- if (state->regs[reg].ok) {
+ if (state->regs[reg].ok && state->regs[reg].kind == TSR_KIND_TYPE) {
int tag = dwarf_tag(&state->regs[reg].type);

pr_debug_dtp("\n");
@@ -893,10 +985,25 @@ static bool check_matching_type(struct type_state *state,
return true;
}

+ if (state->regs[reg].kind == TSR_KIND_PERCPU_BASE) {
+ u64 var_addr = dloc->op->offset;
+ int var_offset;
+
+ pr_debug_dtp(" percpu var\n");
+
+ if (get_global_var_type(cu_die, dloc, dloc->ip, var_addr,
+ &var_offset, type_die)) {
+ dloc->type_offset = var_offset;
+ return true;
+ }
+ return false;
+ }
+
if (map__dso(dloc->ms->map)->kernel && arch__is(dloc->arch, "x86")) {
u64 addr;
int offset;

+ /* Direct this-cpu access like "%gs:0x34740" */
if (dloc->op->segment == INSN_SEG_X86_GS && dloc->op->imm) {
pr_debug_dtp(" this-cpu var\n");

@@ -907,6 +1014,24 @@ static bool check_matching_type(struct type_state *state,
dloc->type_offset = offset;
return true;
}
+ return false;
+ }
+
+ /* Access to per-cpu base like "-0x7dcf0500(,%rdx,8)" */
+ if (dloc->op->offset < 0 && reg != state->stack_reg) {
+ const char *var_name = NULL;
+
+ addr = (s64) dloc->op->offset;
+
+ if (get_global_var_info(dloc, addr, &var_name, &offset) &&
+ !strcmp(var_name, "__per_cpu_offset") && offset == 0 &&
+ get_global_var_type(cu_die, dloc, dloc->ip, addr,
+ &offset, type_die)) {
+ pr_debug_dtp(" percpu base\n");
+
+ dloc->type_offset = offset;
+ return true;
+ }
}
}

@@ -1015,7 +1140,7 @@ static int find_data_type_block(struct data_loc_info *dloc, int reg,
ret = 0;
pr_debug_dtp("found by insn track: %#x(reg%d) type-offset=%#x",
dloc->op->offset, reg, dloc->type_offset);
- pr_debug_type_name(type_die);
+ pr_debug_type_name(type_die, TSR_KIND_TYPE);
break;
}

@@ -1147,7 +1272,7 @@ static int find_data_type_die(struct data_loc_info *dloc, Dwarf_Die *type_die)
loc->offset, reg, fb_offset, offset);
else
pr_debug_dtp("%#x(reg%d)", loc->offset, reg);
- pr_debug_type_name(type_die);
+ pr_debug_type_name(type_die, TSR_KIND_TYPE);
}
dloc->type_offset = offset;
goto out;
--
2.44.0.291.gc1ea87d7ee-goog