[PATCH v4 05/19] gendwarfksyms: Add a cache for processed DIEs

Sami Tolvanen
2024-10-08T18:38:46Z

Basic types in DWARF repeat frequently and traversing the DIEs using
libdw is relatively slow. Add a simple hashtable based cache for the
processed DIEs.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Acked-by: Neal Gompa <neal@gompa.dev>
---
scripts/gendwarfksyms/Makefile | 1 +
scripts/gendwarfksyms/die.c | 143 ++++++++++++++++++++++++++
scripts/gendwarfksyms/dwarf.c | 136 +++++++++++++++++-------
scripts/gendwarfksyms/gendwarfksyms.c | 6 ++
scripts/gendwarfksyms/gendwarfksyms.h | 63 +++++++++++-
5 files changed, 308 insertions(+), 41 deletions(-)
create mode 100644 scripts/gendwarfksyms/die.c

diff --git a/scripts/gendwarfksyms/Makefile b/scripts/gendwarfksyms/Makefile
index 9f8fec4fd39b..c0d4ce50fc27 100644
--- a/scripts/gendwarfksyms/Makefile
+++ b/scripts/gendwarfksyms/Makefile
@@ -2,6 +2,7 @@
hostprogs-always-y += gendwarfksyms

gendwarfksyms-objs += gendwarfksyms.o
+gendwarfksyms-objs += die.o
gendwarfksyms-objs += dwarf.o
gendwarfksyms-objs += symbols.o

diff --git a/scripts/gendwarfksyms/die.c b/scripts/gendwarfksyms/die.c
new file mode 100644
index 000000000000..28d89fce89fc
--- /dev/null
+++ b/scripts/gendwarfksyms/die.c
@@ -0,0 +1,143 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2024 Google LLC
+ */
+
+#include <string.h>
+#include "gendwarfksyms.h"
+
+#define DIE_HASH_BITS 20
+
+/* {die->addr, state} -> struct die * */
+static HASHTABLE_DEFINE(die_map, 1 << DIE_HASH_BITS);
+
+static unsigned int map_hits;
+static unsigned int map_misses;
+
+static inline unsigned int die_hash(uintptr_t addr, enum die_state state)
+{
+ return hash_32(addr_hash(addr) ^ (unsigned int)state);
+}
+
+static void init_die(struct die *cd)
+{
+ cd->state = DIE_INCOMPLETE;
+ cd->fqn = NULL;
+ cd->tag = -1;
+ cd->addr = 0;
+ INIT_LIST_HEAD(&cd->fragments);
+}
+
+static struct die *create_die(Dwarf_Die *die, enum die_state state)
+{
+ struct die *cd;
+
+ cd = xmalloc(sizeof(struct die));
+ init_die(cd);
+ cd->addr = (uintptr_t)die->addr;
+
+ hash_add(die_map, &cd->hash, die_hash(cd->addr, state));
+ return cd;
+}
+
+int __die_map_get(uintptr_t addr, enum die_state state, struct die **res)
+{
+ struct die *cd;
+
+ hash_for_each_possible(die_map, cd, hash, die_hash(addr, state)) {
+ if (cd->addr == addr && cd->state == state) {
+ *res = cd;
+ return 0;
+ }
+ }
+
+ return -1;
+}
+
+struct die *die_map_get(Dwarf_Die *die, enum die_state state)
+{
+ struct die *cd;
+
+ if (__die_map_get((uintptr_t)die->addr, state, &cd) == 0) {
+ map_hits++;
+ return cd;
+ }
+
+ map_misses++;
+ return create_die(die, state);
+}
+
+static void reset_die(struct die *cd)
+{
+ struct die_fragment *tmp;
+ struct die_fragment *df;
+
+ list_for_each_entry_safe(df, tmp, &cd->fragments, list) {
+ if (df->type == FRAGMENT_STRING)
+ free(df->data.str);
+ free(df);
+ }
+
+ if (cd->fqn && *cd->fqn)
+ free(cd->fqn);
+ init_die(cd);
+}
+
+void die_map_free(void)
+{
+ struct hlist_node *tmp;
+ unsigned int stats[DIE_LAST + 1];
+ struct die *cd;
+ int i;
+
+ memset(stats, 0, sizeof(stats));
+
+ hash_for_each_safe(die_map, cd, tmp, hash) {
+ stats[cd->state]++;
+ reset_die(cd);
+ free(cd);
+ }
+ hash_init(die_map);
+
+ if (map_hits + map_misses > 0)
+ debug("hits %u, misses %u (hit rate %.02f%%)", map_hits,
+ map_misses,
+ (100.0f * map_hits) / (map_hits + map_misses));
+
+ for (i = 0; i <= DIE_LAST; i++)
+ debug("%s: %u entries", die_state_name(i), stats[i]);
+}
+
+static struct die_fragment *append_item(struct die *cd)
+{
+ struct die_fragment *df;
+
+ df = xmalloc(sizeof(struct die_fragment));
+ df->type = FRAGMENT_EMPTY;
+ list_add_tail(&df->list, &cd->fragments);
+ return df;
+}
+
+void die_map_add_string(struct die *cd, const char *str)
+{
+ struct die_fragment *df;
+
+ if (!cd)
+ return;
+
+ df = append_item(cd);
+ df->data.str = xstrdup(str);
+ df->type = FRAGMENT_STRING;
+}
+
+void die_map_add_die(struct die *cd, struct die *child)
+{
+ struct die_fragment *df;
+
+ if (!cd)
+ return;
+
+ df = append_item(cd);
+ df->data.addr = child->addr;
+ df->type = FRAGMENT_DIE;
+}
diff --git a/scripts/gendwarfksyms/dwarf.c b/scripts/gendwarfksyms/dwarf.c
index 35fd1dfeeadc..c2cd4743515e 100644
--- a/scripts/gendwarfksyms/dwarf.c
+++ b/scripts/gendwarfksyms/dwarf.c
@@ -71,17 +71,19 @@ static bool match_export_symbol(struct state *state, Dwarf_Die *die)
/*
* Type string processing
*/
-static void process(const char *s)
+static void process(struct die *cache, const char *s)
{
s = s ?: "<null>";

if (dump_dies)
fputs(s, stderr);
+
+ die_map_add_string(cache, s);
}

#define MAX_FMT_BUFFER_SIZE 128

-static void process_fmt(const char *fmt, ...)
+static void process_fmt(struct die *cache, const char *fmt, ...)
{
char buf[MAX_FMT_BUFFER_SIZE];
va_list args;
@@ -91,7 +93,7 @@ static void process_fmt(const char *fmt, ...)
if (checkp(vsnprintf(buf, sizeof(buf), fmt, args)) >= sizeof(buf))
error("vsnprintf overflow: increase MAX_FMT_BUFFER_SIZE");

- process(buf);
+ process(cache, buf);
va_end(args);
}

@@ -164,18 +166,28 @@ static char *get_fqn(Dwarf_Die *die)
return fqn;
}

-static void process_fqn(Dwarf_Die *die)
+static void update_fqn(struct die *cache, Dwarf_Die *die)
+{
+ if (!cache->fqn)
+ cache->fqn = get_fqn(die) ?: "";
+}
+
+static void process_fqn(struct die *cache, Dwarf_Die *die)
{
- process(" ");
- process(get_fqn(die) ?: "");
+ update_fqn(cache, die);
+ if (*cache->fqn)
+ process(cache, " ");
+ process(cache, cache->fqn);
}

-#define DEFINE_PROCESS_UDATA_ATTRIBUTE(attribute) \
- static void process_##attribute##_attr(Dwarf_Die *die) \
- { \
- Dwarf_Word value; \
- if (get_udata_attr(die, DW_AT_##attribute, &value)) \
- process_fmt(" " #attribute "(%" PRIu64 ")", value); \
+#define DEFINE_PROCESS_UDATA_ATTRIBUTE(attribute) \
+ static void process_##attribute##_attr(struct die *cache, \
+ Dwarf_Die *die) \
+ { \
+ Dwarf_Word value; \
+ if (get_udata_attr(die, DW_AT_##attribute, &value)) \
+ process_fmt(cache, " " #attribute "(%" PRIu64 ")", \
+ value); \
}

DEFINE_PROCESS_UDATA_ATTRIBUTE(alignment)
@@ -187,8 +199,9 @@ bool match_all(Dwarf_Die *die)
return true;
}

-int process_die_container(struct state *state, Dwarf_Die *die,
- die_callback_t func, die_match_callback_t match)
+int process_die_container(struct state *state, struct die *cache,
+ Dwarf_Die *die, die_callback_t func,
+ die_match_callback_t match)
{
Dwarf_Die current;
int res;
@@ -197,7 +210,7 @@ int process_die_container(struct state *state, Dwarf_Die *die,
while (!res) {
if (match(&current)) {
/* <0 = error, 0 = continue, >0 = stop */
- res = checkp(func(state, &current));
+ res = checkp(func(state, cache, &current));
if (res)
return res;
}
@@ -208,39 +221,78 @@ int process_die_container(struct state *state, Dwarf_Die *die,
return 0;
}

-static int process_type(struct state *state, Dwarf_Die *die);
+static int process_type(struct state *state, struct die *parent,
+ Dwarf_Die *die);

-static void process_type_attr(struct state *state, Dwarf_Die *die)
+static void process_type_attr(struct state *state, struct die *cache,
+ Dwarf_Die *die)
{
Dwarf_Die type;

if (get_ref_die_attr(die, DW_AT_type, &type)) {
- check(process_type(state, &type));
+ check(process_type(state, cache, &type));
return;
}

/* Compilers can omit DW_AT_type -- print out 'void' to clarify */
- process("base_type void");
+ process(cache, "base_type void");
+}
+
+static void process_base_type(struct state *state, struct die *cache,
+ Dwarf_Die *die)
+{
+ process(cache, "base_type");
+ process_fqn(cache, die);
+ process_byte_size_attr(cache, die);
+ process_encoding_attr(cache, die);
+ process_alignment_attr(cache, die);
}

-static void process_base_type(struct state *state, Dwarf_Die *die)
+static void process_cached(struct state *state, struct die *cache,
+ Dwarf_Die *die)
{
- process("base_type");
- process_fqn(die);
- process_byte_size_attr(die);
- process_encoding_attr(die);
- process_alignment_attr(die);
+ struct die_fragment *df;
+ Dwarf_Die child;
+
+ list_for_each_entry(df, &cache->fragments, list) {
+ switch (df->type) {
+ case FRAGMENT_STRING:
+ process(NULL, df->data.str);
+ break;
+ case FRAGMENT_DIE:
+ if (!dwarf_die_addr_die(dwarf_cu_getdwarf(die->cu),
+ (void *)df->data.addr, &child))
+ error("dwarf_die_addr_die failed");
+ check(process_type(state, NULL, &child));
+ break;
+ default:
+ error("empty die_fragment");
+ }
+ }
}

-#define PROCESS_TYPE(type) \
- case DW_TAG_##type##_type: \
- process_##type##_type(state, die); \
+#define PROCESS_TYPE(type) \
+ case DW_TAG_##type##_type: \
+ process_##type##_type(state, cache, die); \
break;

-static int process_type(struct state *state, Dwarf_Die *die)
+static int process_type(struct state *state, struct die *parent, Dwarf_Die *die)
{
+ struct die *cache;
int tag = dwarf_tag(die);

+ /*
+ * If we have the DIE already cached, use it instead of walking
+ * through DWARF.
+ */
+ cache = die_map_get(die, DIE_COMPLETE);
+
+ if (cache->state == DIE_COMPLETE) {
+ process_cached(state, cache, die);
+ die_map_add_die(parent, cache);
+ return 0;
+ }
+
switch (tag) {
PROCESS_TYPE(base)
default:
@@ -248,6 +300,11 @@ static int process_type(struct state *state, Dwarf_Die *die)
break;
}

+ /* Update cache state and append to the parent (if any) */
+ cache->tag = tag;
+ cache->state = DIE_COMPLETE;
+ die_map_add_die(parent, cache);
+
return 0;
}

@@ -258,14 +315,15 @@ static void process_symbol(struct state *state, Dwarf_Die *die,
die_callback_t process_func)
{
debug("%s", state->sym->name);
- check(process_func(state, die));
+ check(process_func(state, NULL, die));
if (dump_dies)
fputs("\n", stderr);
}

-static int __process_subprogram(struct state *state, Dwarf_Die *die)
+static int __process_subprogram(struct state *state, struct die *cache,
+ Dwarf_Die *die)
{
- process("subprogram");
+ process(cache, "subprogram");
return 0;
}

@@ -274,10 +332,11 @@ static void process_subprogram(struct state *state, Dwarf_Die *die)
process_symbol(state, die, __process_subprogram);
}

-static int __process_variable(struct state *state, Dwarf_Die *die)
+static int __process_variable(struct state *state, struct die *cache,
+ Dwarf_Die *die)
{
- process("variable ");
- process_type_attr(state, die);
+ process(cache, "variable ");
+ process_type_attr(state, cache, die);
return 0;
}

@@ -286,7 +345,8 @@ static void process_variable(struct state *state, Dwarf_Die *die)
process_symbol(state, die, __process_variable);
}

-static int process_exported_symbols(struct state *unused, Dwarf_Die *die)
+static int process_exported_symbols(struct state *unused, struct die *cache,
+ Dwarf_Die *die)
{
int tag = dwarf_tag(die);

@@ -296,7 +356,7 @@ static int process_exported_symbols(struct state *unused, Dwarf_Die *die)
case DW_TAG_class_type:
case DW_TAG_structure_type:
return check(process_die_container(
- NULL, die, process_exported_symbols, match_all));
+ NULL, cache, die, process_exported_symbols, match_all));

/* Possible exported symbols */
case DW_TAG_subprogram:
@@ -320,6 +380,6 @@ static int process_exported_symbols(struct state *unused, Dwarf_Die *die)

void process_cu(Dwarf_Die *cudie)
{
- check(process_die_container(NULL, cudie, process_exported_symbols,
+ check(process_die_container(NULL, NULL, cudie, process_exported_symbols,
match_all));
}
diff --git a/scripts/gendwarfksyms/gendwarfksyms.c b/scripts/gendwarfksyms/gendwarfksyms.c
index 6fb12f9f6023..310cc9257d6e 100644
--- a/scripts/gendwarfksyms/gendwarfksyms.c
+++ b/scripts/gendwarfksyms/gendwarfksyms.c
@@ -43,6 +43,10 @@ static int process_module(Dwfl_Module *mod, void **userdata, const char *name,
debug("%s", name);
dbg = dwfl_module_getdwarf(mod, &dwbias);

+ /*
+ * Look for exported symbols in each CU, follow the DIE tree, and add
+ * the entries to die_map.
+ */
do {
res = dwarf_get_units(dbg, cu, &cu, NULL, NULL, &cudie, NULL);
if (res < 0)
@@ -53,6 +57,8 @@ static int process_module(Dwfl_Module *mod, void **userdata, const char *name,
process_cu(&cudie);
} while (cu);

+ die_map_free();
+
return DWARF_CB_OK;
}

diff --git a/scripts/gendwarfksyms/gendwarfksyms.h b/scripts/gendwarfksyms/gendwarfksyms.h
index a058647e2361..da0db7a0c093 100644
--- a/scripts/gendwarfksyms/gendwarfksyms.h
+++ b/scripts/gendwarfksyms/gendwarfksyms.h
@@ -89,6 +89,61 @@ void symbol_read_exports(FILE *file);
void symbol_read_symtab(int fd);
struct symbol *symbol_get(const char *name);

+/*
+ * die.c
+ */
+
+enum die_state {
+ DIE_INCOMPLETE,
+ DIE_COMPLETE,
+ DIE_LAST = DIE_COMPLETE
+};
+
+enum die_fragment_type {
+ FRAGMENT_EMPTY,
+ FRAGMENT_STRING,
+ FRAGMENT_DIE
+};
+
+struct die_fragment {
+ enum die_fragment_type type;
+ union {
+ char *str;
+ uintptr_t addr;
+ } data;
+ struct list_head list;
+};
+
+#define CASE_CONST_TO_STR(name) \
+ case name: \
+ return #name;
+
+static inline const char *die_state_name(enum die_state state)
+{
+ switch (state) {
+ CASE_CONST_TO_STR(DIE_INCOMPLETE)
+ CASE_CONST_TO_STR(DIE_COMPLETE)
+ }
+
+ error("unexpected die_state: %d", state);
+}
+
+struct die {
+ enum die_state state;
+ char *fqn;
+ int tag;
+ uintptr_t addr;
+ struct list_head fragments;
+ struct hlist_node hash;
+};
+
+int __die_map_get(uintptr_t addr, enum die_state state, struct die **res);
+struct die *die_map_get(Dwarf_Die *die, enum die_state state);
+void die_map_add_string(struct die *pd, const char *str);
+void die_map_add_linebreak(struct die *pd, int linebreak);
+void die_map_add_die(struct die *pd, struct die *child);
+void die_map_free(void);
+
/*
* dwarf.c
*/
@@ -98,12 +153,14 @@ struct state {
Dwarf_Die die;
};

-typedef int (*die_callback_t)(struct state *state, Dwarf_Die *die);
+typedef int (*die_callback_t)(struct state *state, struct die *cache,
+ Dwarf_Die *die);
typedef bool (*die_match_callback_t)(Dwarf_Die *die);
bool match_all(Dwarf_Die *die);

-int process_die_container(struct state *state, Dwarf_Die *die,
- die_callback_t func, die_match_callback_t match);
+int process_die_container(struct state *state, struct die *cache,
+ Dwarf_Die *die, die_callback_t func,
+ die_match_callback_t match);

void process_cu(Dwarf_Die *cudie);