If it failed to find a variable for the location directly, it might be
due to a missing variable in the source code. For example, accessing
pointer variables in a chain can result in the case like below:
struct foo *foo = ...;
int i = foo->bar->baz;
The DWARF debug information is created for each variable so it'd have
one for 'foo'. But there's no variable for 'foo->bar' and then it
cannot know the type of 'bar' and 'baz'.
The above source code can be compiled to the follow x86 instructions:
mov 0x8(%rax), %rcx
mov 0x4(%rcx), %rdx <=== PMU sample
mov %rdx, -4(%rbp)
Let's say 'foo' is located in the %rax and it has a pointer to struct
foo. But perf sample is captured in the second instruction and there
is no variable or type info for the %rcx.
It'd be great if compiler could generate debug info for %rcx, but we
should handle it on our side. So this patch implements the logic to
iterate instructions and update the type table for each location.
As it already collected a list of scopes including the target
instruction, we can use it to construct the type table smartly.
+---------------- scope[0] subprogram
|
| +-------------- scope[1] lexical_block
| |
| | +------------ scope[2] inlined_subroutine
| | |
| | | +---------- scope[3] inlined_subroutine
| | | |
| | | | +-------- scope[4] lexical_block
| | | | |
| | | | | *** target instruction
...
Image the target instruction has 5 scopes, each scope will have its own
variables and parameters. Then it can start with the innermost scope
(4). So it'd search the shortest path from the start of scope[4] to
the target address and build a list of basic blocks. Then it iterates
the basic blocks with the variables in the scope and update the table.
If it finds a type at the target instruction, then returns it.
Otherwise, it moves to the upper scope[3]. Now it'd search the shortest
path from the start of scope[3] to the start of scope[4]. Then connect
it to the existing basic block list. Then it'd iterate the blocks with
variables for both scopes. It can repeat this until it finds a type at
the target instruction or reaches to the top scope[0].
As the basic blocks contain the shortest path, it won't worry about
branches and can update the table simply.
With this change, the stat now looks like below:
Annotate data type stats:
total 294, ok 185 (62.9%), bad 109 (37.1%)
-----------------------------------------------------------
30 : no_sym
32 : no_mem_ops
27 : no_var
13 : no_typeinfo
7 : bad_offset
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
tools/perf/util/annotate-data.c | 232 ++++++++++++++++++++++++++++++++
1 file changed, 232 insertions(+)
@@ -597,6 +597,231 @@ void update_insn_state(struct type_state *state, struct data_loc_info *dloc,
/* Case 4. memory to memory transfers (not handled for now) */
}
+/* Prepend this_list to full_list, removing duplicate disasm line */
+static void prepend_basic_blocks(struct list_head *this_blocks,
+ struct list_head *full_blocks)
+{
+ struct annotated_basic_block *first_bb, *last_bb;
+
+ last_bb = list_last_entry(this_blocks, typeof(*last_bb), list);
+ first_bb = list_first_entry(full_blocks, typeof(*first_bb), list);
+
+ if (list_empty(full_blocks))
+ goto out;
+
+ if (last_bb->end != first_bb->begin) {
+ pr_debug("prepend basic blocks: mismatched disasm line %lx -> %lx\n",
+ last_bb->end->al.offset, first_bb->begin->al.offset);
+ goto out;
+ }
+
+ /* Is the basic block have only one disasm_line? */
+ if (last_bb->begin == last_bb->end) {
+ list_del(&last_bb->list);
+ free(last_bb);
+ goto out;
+ }
+
+ last_bb->end = list_prev_entry(last_bb->end, al.node);
+
+out:
+ list_splice(this_blocks, full_blocks);
+}
+
+static void delete_basic_blocks(struct list_head *basic_blocks)
+{
+ struct annotated_basic_block *bb, *tmp;
+
+ list_for_each_entry_safe(bb, tmp, basic_blocks, list) {
+ list_del(&bb->list);
+ free(bb);
+ }
+}
+
+/* Make sure all variables have a valid start address */
+static void fixup_var_address(struct die_var_type *var_types, u64 addr)
+{
+ while (var_types) {
+ /*
+ * Some variables have no address range meaning it's always
+ * available in the whole scope. Let's adjust the start
+ * address to the start of the scope.
+ */
+ if (var_types->addr == 0)
+ var_types->addr = addr;
+
+ var_types = var_types->next;
+ }
+}
+
+static void delete_var_types(struct die_var_type *var_types)
+{
+ while (var_types) {
+ struct die_var_type *next = var_types->next;
+
+ free(var_types);
+ var_types = next;
+ }
+}
+
+/* It's at the target address, check if it has a matching type */
+static bool find_matching_type(struct type_state *state,
+ struct data_loc_info *dloc, int reg,
+ Dwarf_Die *type_die)
+{
+ Dwarf_Word size;
+
+ if (state->regs[reg].ok) {
+ int tag = dwarf_tag(&state->regs[reg].type);
+
+ /*
+ * Normal registers should hold a pointer (or array) to
+ * dereference a memory location.
+ */
+ if (tag != DW_TAG_pointer_type && tag != DW_TAG_array_type)
+ return false;
+
+ if (die_get_real_type(&state->regs[reg].type, type_die) == NULL)
+ return false;
+
+ dloc->type_offset = dloc->op->offset;
+
+ /* Get the size of the actual type */
+ if (dwarf_aggregate_size(type_die, &size) < 0 ||
+ (unsigned)dloc->type_offset >= size)
+ return false;
+
+ return true;
+ }
+
+ if (reg == dloc->fbreg) {
+ struct type_state_stack *stack;
+
+ stack = find_stack_state(state, dloc->type_offset);
+ if (stack == NULL)
+ return false;
+
+ *type_die = stack->type;
+ /* Update the type offset from the start of slot */
+ dloc->type_offset -= stack->offset;
+ return true;
+ }
+
+ if (dloc->fb_cfa) {
+ struct type_state_stack *stack;
+ u64 pc = map__rip_2objdump(dloc->ms->map, dloc->ip);
+ int fbreg, fboff;
+
+ if (die_get_cfa(dloc->di->dbg, pc, &fbreg, &fboff) < 0)
+ fbreg = -1;
+
+ if (reg != fbreg)
+ return false;
+
+ stack = find_stack_state(state, dloc->type_offset - fboff);
+ if (stack == NULL)
+ return false;
+
+ *type_die = stack->type;
+ /* Update the type offset from the start of slot */
+ dloc->type_offset -= fboff + stack->offset;
+ return true;
+ }
+
+ return false;
+}
+
+/* Iterate instructions in basic blocks and update type table */
+static bool find_data_type_insn(struct data_loc_info *dloc, int reg,
+ struct list_head *basic_blocks,
+ struct die_var_type *var_types,
+ Dwarf_Die *cu_die, Dwarf_Die *type_die)
+{
+ struct type_state state;
+ struct symbol *sym = dloc->ms->sym;
+ struct annotation *notes = symbol__annotation(sym);
+ struct annotated_basic_block *bb;
+ bool found = false;
+
+ init_type_state(&state, dloc->arch);
+
+ list_for_each_entry(bb, basic_blocks, list) {
+ struct disasm_line *dl = bb->begin;
+
+ list_for_each_entry_from(dl, ¬es->src->source, al.node) {
+ u64 this_ip = sym->start + dl->al.offset;
+ u64 addr = map__rip_2objdump(dloc->ms->map, this_ip);
+
+ /* Update variable type at this address */
+ update_var_state(&state, dloc, addr, var_types);
+
+ if (this_ip == dloc->ip) {
+ found = find_matching_type(&state, dloc, reg,
+ type_die);
+ goto out;
+ }
+
+ /* Update type table after processing the instruction */
+ update_insn_state(&state, dloc, cu_die, dl);
+ if (dl == bb->end)
+ break;
+ }
+ }
+
+out:
+ exit_type_state(&state);
+ return found;
+}
+
+/*
+ * Construct a list of basic blocks for each scope with variables and try to find
+ * the data type by updating a type state table through instructions.
+ */
+static int find_data_type_block(struct data_loc_info *dloc, int reg,
+ Dwarf_Die *cu_die, Dwarf_Die *scopes,
+ int nr_scopes, Dwarf_Die *type_die)
+{
+ LIST_HEAD(basic_blocks);
+ struct die_var_type *var_types = NULL;
+ u64 src_ip, dst_ip;
+ int ret = -1;
+
+ dst_ip = dloc->ip;
+ for (int i = nr_scopes - 1; i >= 0; i--) {
+ Dwarf_Addr base, start, end;
+ LIST_HEAD(this_blocks);
+
+ if (dwarf_ranges(&scopes[i], 0, &base, &start, &end) < 0)
+ break;
+
+ src_ip = map__objdump_2rip(dloc->ms->map, start);
+
+ /* Get basic blocks for this scope */
+ if (annotate_get_basic_blocks(dloc->ms->sym, src_ip, dst_ip,
+ &this_blocks) < 0)
+ continue;
+ prepend_basic_blocks(&this_blocks, &basic_blocks);
+
+ /* Get variable info for this scope and add to var_types list */
+ die_collect_vars(&scopes[i], &var_types);
+ fixup_var_address(var_types, start);
+
+ /* Find from start of this scope to the target instruction */
+ if (find_data_type_insn(dloc, reg, &basic_blocks, var_types,
+ cu_die, type_die)) {
+ ret = 0;
+ break;
+ }
+
+ /* Go up to the next scope and find blocks to the start */
+ dst_ip = src_ip;
+ }
+
+ delete_basic_blocks(&basic_blocks);
+ delete_var_types(var_types);
+ 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)
{
@@ -697,6 +922,13 @@ static int find_data_type_die(struct data_loc_info *dloc, Dwarf_Die *type_die)
goto out;
}
+ if (reg != DWARF_REG_PC) {
+ ret = find_data_type_block(dloc, reg, &cu_die, scopes,
+ nr_scopes, type_die);
+ if (ret == 0)
+ goto out;
+ }
+
if (loc->multi_regs && reg == loc->reg1 && loc->reg1 != loc->reg2) {
reg = loc->reg2;
goto retry;