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libbpf: Extract internal set-of-strings datastructure APIs

Browse source 
Extract BTF logic for maintaining a set of strings data structure, used for
BTF strings section construction in writable mode, into separate re-usable
API. This data structure is going to be used by bpf_linker to maintains ELF
STRTAB section, which has the same layout as BTF strings section.

Suggested-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210318194036.3521577-5-andrii@kernel.org
This commit is contained in:
Andrii Nakryiko 2021-03-18 12:40:28 -07:00 • committed by Alexei Starovoitov
parent 3b029e06f6
commit 90d76d3ece
4 changed files with 259 additions and 195 deletions
Download patch file Download diff file Expand all files Collapse all files

2
tools/lib/bpf/Build
View file

@ -1,3 +1,3 @@
libbpf-y := libbpf.o bpf.o nlattr.o btf.o libbpf_errno.o str_error.o \ libbpf-y := libbpf.o bpf.o nlattr.o btf.o libbpf_errno.o str_error.o \
netlink.o bpf_prog_linfo.o libbpf_probes.o xsk.o hashmap.o \ netlink.o bpf_prog_linfo.o libbpf_probes.o xsk.o hashmap.o \
btf_dump.o ringbuf.o btf_dump.o ringbuf.o strset.o

255
tools/lib/bpf/btf.c
View file

@ -21,6 +21,7 @@
#include "libbpf.h" #include "libbpf.h"
#include "libbpf_internal.h" #include "libbpf_internal.h"
#include "hashmap.h" #include "hashmap.h"
#include "strset.h"
#define BTF_MAX_NR_TYPES 0x7fffffffU #define BTF_MAX_NR_TYPES 0x7fffffffU
#define BTF_MAX_STR_OFFSET 0x7fffffffU #define BTF_MAX_STR_OFFSET 0x7fffffffU
@ -67,7 +68,7 @@ struct btf {
* | | | * | | |
* hdr | | * hdr | |
* types_data----+ | * types_data----+ |
* strs_data------------------+ * strset__data(strs_set)-----+
* *
* +----------+---------+-----------+ * +----------+---------+-----------+
* | Header | Types | Strings | * | Header | Types | Strings |
@ -105,20 +106,15 @@ struct btf {
*/ */
int start_str_off; int start_str_off;
/* only one of strs_data or strs_set can be non-NULL, depending on
* whether BTF is in a modifiable state (strs_set is used) or not
* (strs_data points inside raw_data)
*/
void *strs_data; void *strs_data;
size_t strs_data_cap; /* used size stored in hdr->str_len */ /* a set of unique strings */
struct strset *strs_set;
/* lookup index for each unique string in strings section */
struct hashmap *strs_hash;
/* whether strings are already deduplicated */ /* whether strings are already deduplicated */
bool strs_deduped; bool strs_deduped;
/* extra indirection layer to make strings hashmap work with stable
* string offsets and ability to transparently choose between
* btf->strs_data or btf_dedup->strs_data as a source of strings.
* This is used for BTF strings dedup to transfer deduplicated strings
* data back to struct btf without re-building strings index.
*/
void **strs_data_ptr;
/* BTF object FD, if loaded into kernel */ /* BTF object FD, if loaded into kernel */
int fd; int fd;
@ -738,7 +734,7 @@ void btf__free(struct btf *btf)
*/ */
free(btf->hdr); free(btf->hdr);
free(btf->types_data); free(btf->types_data);
free(btf->strs_data); strset__free(btf->strs_set);
} }
free(btf->raw_data); free(btf->raw_data);
free(btf->raw_data_swapped); free(btf->raw_data_swapped);
@ -1246,6 +1242,11 @@ void btf__set_fd(struct btf *btf, int fd)
btf->fd = fd; btf->fd = fd;
} }
static const void *btf_strs_data(const struct btf *btf)
{
return btf->strs_data ? btf->strs_data : strset__data(btf->strs_set);
}
static void *btf_get_raw_data(const struct btf *btf, __u32 *size, bool swap_endian) static void *btf_get_raw_data(const struct btf *btf, __u32 *size, bool swap_endian)
{ {
struct btf_header *hdr = btf->hdr; struct btf_header *hdr = btf->hdr;
@ -1286,7 +1287,7 @@ static void *btf_get_raw_data(const struct btf *btf, __u32 *size, bool swap_endi
} }
p += hdr->type_len; p += hdr->type_len;
memcpy(p, btf->strs_data, hdr->str_len); memcpy(p, btf_strs_data(btf), hdr->str_len);
p += hdr->str_len; p += hdr->str_len;
*size = data_sz; *size = data_sz;
@ -1320,7 +1321,7 @@ const char *btf__str_by_offset(const struct btf *btf, __u32 offset)
if (offset < btf->start_str_off) if (offset < btf->start_str_off)
return btf__str_by_offset(btf->base_btf, offset); return btf__str_by_offset(btf->base_btf, offset);
else if (offset - btf->start_str_off < btf->hdr->str_len) else if (offset - btf->start_str_off < btf->hdr->str_len)
return btf->strs_data + (offset - btf->start_str_off); return btf_strs_data(btf) + (offset - btf->start_str_off);
else else
return NULL; return NULL;
} }
@ -1474,25 +1475,6 @@ int btf__get_map_kv_tids(const struct btf *btf, const char *map_name,
return 0; return 0;
} }
static size_t strs_hash_fn(const void *key, void *ctx)
{
const struct btf *btf = ctx;
const char *strs = *btf->strs_data_ptr;
const char *str = strs + (long)key;
return str_hash(str);
}
static bool strs_hash_equal_fn(const void *key1, const void *key2, void *ctx)
{
const struct btf *btf = ctx;
const char *strs = *btf->strs_data_ptr;
const char *str1 = strs + (long)key1;
const char *str2 = strs + (long)key2;
return strcmp(str1, str2) == 0;
}
static void btf_invalidate_raw_data(struct btf *btf) static void btf_invalidate_raw_data(struct btf *btf)
{ {
if (btf->raw_data) { if (btf->raw_data) {
@ -1511,10 +1493,9 @@ static void btf_invalidate_raw_data(struct btf *btf)
*/ */
static int btf_ensure_modifiable(struct btf *btf) static int btf_ensure_modifiable(struct btf *btf)
{ {
void *hdr, *types, *strs, *strs_end, *s; void *hdr, *types;
struct hashmap *hash = NULL; struct strset *set = NULL;
long off; int err = -ENOMEM;
int err;
if (btf_is_modifiable(btf)) { if (btf_is_modifiable(btf)) {
/* any BTF modification invalidates raw_data */ /* any BTF modification invalidates raw_data */
@ -1525,44 +1506,25 @@ static int btf_ensure_modifiable(struct btf *btf)
/* split raw data into three memory regions */ /* split raw data into three memory regions */
hdr = malloc(btf->hdr->hdr_len); hdr = malloc(btf->hdr->hdr_len);
types = malloc(btf->hdr->type_len); types = malloc(btf->hdr->type_len);
strs = malloc(btf->hdr->str_len); if (!hdr || !types)
if (!hdr || !types || !strs)
goto err_out; goto err_out;
memcpy(hdr, btf->hdr, btf->hdr->hdr_len); memcpy(hdr, btf->hdr, btf->hdr->hdr_len);
memcpy(types, btf->types_data, btf->hdr->type_len); memcpy(types, btf->types_data, btf->hdr->type_len);
memcpy(strs, btf->strs_data, btf->hdr->str_len);
/* make hashmap below use btf->strs_data as a source of strings */
btf->strs_data_ptr = &btf->strs_data;
/* build lookup index for all strings */ /* build lookup index for all strings */
hash = hashmap__new(strs_hash_fn, strs_hash_equal_fn, btf); set = strset__new(BTF_MAX_STR_OFFSET, btf->strs_data, btf->hdr->str_len);
if (IS_ERR(hash)) { if (IS_ERR(set)) {
err = PTR_ERR(hash); err = PTR_ERR(set);
hash = NULL;
goto err_out; goto err_out;
} }
strs_end = strs + btf->hdr->str_len;
for (off = 0, s = strs; s < strs_end; off += strlen(s) + 1, s = strs + off) {
/* hashmap__add() returns EEXIST if string with the same
* content already is in the hash map
*/
err = hashmap__add(hash, (void *)off, (void *)off);
if (err == -EEXIST)
continue; /* duplicate */
if (err)
goto err_out;
}
/* only when everything was successful, update internal state */ /* only when everything was successful, update internal state */
btf->hdr = hdr; btf->hdr = hdr;
btf->types_data = types; btf->types_data = types;
btf->types_data_cap = btf->hdr->type_len; btf->types_data_cap = btf->hdr->type_len;
btf->strs_data = strs; btf->strs_data = NULL;
btf->strs_data_cap = btf->hdr->str_len; btf->strs_set = set;
btf->strs_hash = hash;
/* if BTF was created from scratch, all strings are guaranteed to be /* if BTF was created from scratch, all strings are guaranteed to be
* unique and deduplicated * unique and deduplicated
*/ */
@ -1577,17 +1539,10 @@ static int btf_ensure_modifiable(struct btf *btf)
return 0; return 0;
err_out: err_out:
hashmap__free(hash); strset__free(set);
free(hdr); free(hdr);
free(types); free(types);
free(strs); return err;
return -ENOMEM;
}
static void *btf_add_str_mem(struct btf *btf, size_t add_sz)
{
return libbpf_add_mem(&btf->strs_data, &btf->strs_data_cap, 1,
btf->hdr->str_len, BTF_MAX_STR_OFFSET, add_sz);
} }
/* Find an offset in BTF string section that corresponds to a given string *s*. /* Find an offset in BTF string section that corresponds to a given string *s*.
@ -1598,34 +1553,23 @@ static void *btf_add_str_mem(struct btf *btf, size_t add_sz)
*/ */
int btf__find_str(struct btf *btf, const char *s) int btf__find_str(struct btf *btf, const char *s)
{ {
long old_off, new_off, len; int off;
void *p;
if (btf->base_btf) { if (btf->base_btf) {
int ret; off = btf__find_str(btf->base_btf, s);
if (off != -ENOENT)
ret = btf__find_str(btf->base_btf, s); return off;
if (ret != -ENOENT)
return ret;
} }
/* BTF needs to be in a modifiable state to build string lookup index */ /* BTF needs to be in a modifiable state to build string lookup index */
if (btf_ensure_modifiable(btf)) if (btf_ensure_modifiable(btf))
return -ENOMEM; return -ENOMEM;
/* see btf__add_str() for why we do this */ off = strset__find_str(btf->strs_set, s);
len = strlen(s) + 1; if (off < 0)
p = btf_add_str_mem(btf, len); return off;
if (!p)
return -ENOMEM;
new_off = btf->hdr->str_len; return btf->start_str_off + off;
memcpy(p, s, len);
if (hashmap__find(btf->strs_hash, (void *)new_off, (void **)&old_off))
return btf->start_str_off + old_off;
return -ENOENT;
} }
/* Add a string s to the BTF string section. /* Add a string s to the BTF string section.
@ -1635,50 +1579,24 @@ int btf__find_str(struct btf *btf, const char *s)
*/ */
int btf__add_str(struct btf *btf, const char *s) int btf__add_str(struct btf *btf, const char *s)
{ {
long old_off, new_off, len; int off;
void *p;
int err;
if (btf->base_btf) { if (btf->base_btf) {
int ret; off = btf__find_str(btf->base_btf, s);
if (off != -ENOENT)
ret = btf__find_str(btf->base_btf, s); return off;
if (ret != -ENOENT)
return ret;
} }
if (btf_ensure_modifiable(btf)) if (btf_ensure_modifiable(btf))
return -ENOMEM; return -ENOMEM;
/* Hashmap keys are always offsets within btf->strs_data, so to even off = strset__add_str(btf->strs_set, s);
* look up some string from the "outside", we need to first append it if (off < 0)
* at the end, so that it can be addressed with an offset. Luckily, return off;
* until btf->hdr->str_len is incremented, that string is just a piece
* of garbage for the rest of BTF code, so no harm, no foul. On the
* other hand, if the string is unique, it's already appended and
* ready to be used, only a simple btf->hdr->str_len increment away.
*/
len = strlen(s) + 1;
p = btf_add_str_mem(btf, len);
if (!p)
return -ENOMEM;
new_off = btf->hdr->str_len; btf->hdr->str_len = strset__data_size(btf->strs_set);
memcpy(p, s, len);
/* Now attempt to add the string, but only if the string with the same return btf->start_str_off + off;
* contents doesn't exist already (HASHMAP_ADD strategy). If such
* string exists, we'll get its offset in old_off (that's old_key).
*/
err = hashmap__insert(btf->strs_hash, (void *)new_off, (void *)new_off,
HASHMAP_ADD, (const void **)&old_off, NULL);
if (err == -EEXIST)
return btf->start_str_off + old_off; /* duplicated string, return existing offset */
if (err)
return err;
btf->hdr->str_len += len; /* new unique string, adjust data length */
return btf->start_str_off + new_off;
} }
static void *btf_add_type_mem(struct btf *btf, size_t add_sz) static void *btf_add_type_mem(struct btf *btf, size_t add_sz)
@ -3016,10 +2934,7 @@ struct btf_dedup {
/* Various option modifying behavior of algorithm */ /* Various option modifying behavior of algorithm */
struct btf_dedup_opts opts; struct btf_dedup_opts opts;
/* temporary strings deduplication state */ /* temporary strings deduplication state */
void *strs_data; struct strset *strs_set;
size_t strs_cap;
size_t strs_len;
struct hashmap* strs_hash;
}; };
static long hash_combine(long h, long value) static long hash_combine(long h, long value)
@ -3185,10 +3100,8 @@ static int strs_dedup_remap_str_off(__u32 *str_off_ptr, void *ctx)
{ {
struct btf_dedup *d = ctx; struct btf_dedup *d = ctx;
__u32 str_off = *str_off_ptr; __u32 str_off = *str_off_ptr;
long old_off, new_off, len;
const char *s; const char *s;
void *p; int off, err;
int err;
/* don't touch empty string or string in main BTF */ /* don't touch empty string or string in main BTF */
if (str_off == 0 || str_off < d->btf->start_str_off) if (str_off == 0 || str_off < d->btf->start_str_off)
@ -3205,29 +3118,11 @@ static int strs_dedup_remap_str_off(__u32 *str_off_ptr, void *ctx)
return err; return err;
} }
len = strlen(s) + 1; off = strset__add_str(d->strs_set, s);
if (off < 0)
return off;
new_off = d->strs_len; *str_off_ptr = d->btf->start_str_off + off;
p = libbpf_add_mem(&d->strs_data, &d->strs_cap, 1, new_off, BTF_MAX_STR_OFFSET, len);
if (!p)
return -ENOMEM;
memcpy(p, s, len);
/* Now attempt to add the string, but only if the string with the same
* contents doesn't exist already (HASHMAP_ADD strategy). If such
* string exists, we'll get its offset in old_off (that's old_key).
*/
err = hashmap__insert(d->strs_hash, (void *)new_off, (void *)new_off,
HASHMAP_ADD, (const void **)&old_off, NULL);
if (err == -EEXIST) {
*str_off_ptr = d->btf->start_str_off + old_off;
} else if (err) {
return err;
} else {
*str_off_ptr = d->btf->start_str_off + new_off;
d->strs_len += len;
}
return 0; return 0;
} }
@ -3244,39 +3139,23 @@ static int strs_dedup_remap_str_off(__u32 *str_off_ptr, void *ctx)
*/ */
static int btf_dedup_strings(struct btf_dedup *d) static int btf_dedup_strings(struct btf_dedup *d)
{ {
char *s;
int err; int err;
if (d->btf->strs_deduped) if (d->btf->strs_deduped)
return 0; return 0;
/* temporarily switch to use btf_dedup's strs_data for strings for hash d->strs_set = strset__new(BTF_MAX_STR_OFFSET, NULL, 0);
* functions; later we'll just transfer hashmap to struct btf as is, if (IS_ERR(d->strs_set)) {
* along the strs_data err = PTR_ERR(d->strs_set);
*/
d->btf->strs_data_ptr = &d->strs_data;
d->strs_hash = hashmap__new(strs_hash_fn, strs_hash_equal_fn, d->btf);
if (IS_ERR(d->strs_hash)) {
err = PTR_ERR(d->strs_hash);
d->strs_hash = NULL;
goto err_out; goto err_out;
} }
if (!d->btf->base_btf) { if (!d->btf->base_btf) {
s = libbpf_add_mem(&d->strs_data, &d->strs_cap, 1, d->strs_len, BTF_MAX_STR_OFFSET, 1);
if (!s)
return -ENOMEM;
/* initial empty string */
s[0] = 0;
d->strs_len = 1;
/* insert empty string; we won't be looking it up during strings /* insert empty string; we won't be looking it up during strings
* dedup, but it's good to have it for generic BTF string lookups * dedup, but it's good to have it for generic BTF string lookups
*/ */
err = hashmap__insert(d->strs_hash, (void *)0, (void *)0, err = strset__add_str(d->strs_set, "");
HASHMAP_ADD, NULL, NULL); if (err < 0)
if (err)
goto err_out; goto err_out;
} }
@ -3286,28 +3165,16 @@ static int btf_dedup_strings(struct btf_dedup *d)
goto err_out; goto err_out;
/* replace BTF string data and hash with deduped ones */ /* replace BTF string data and hash with deduped ones */
free(d->btf->strs_data); strset__free(d->btf->strs_set);
hashmap__free(d->btf->strs_hash); d->btf->hdr->str_len = strset__data_size(d->strs_set);
d->btf->strs_data = d->strs_data; d->btf->strs_set = d->strs_set;
d->btf->strs_data_cap = d->strs_cap; d->strs_set = NULL;
d->btf->hdr->str_len = d->strs_len;
d->btf->strs_hash = d->strs_hash;
/* now point strs_data_ptr back to btf->strs_data */
d->btf->strs_data_ptr = &d->btf->strs_data;
d->strs_data = d->strs_hash = NULL;
d->strs_len = d->strs_cap = 0;
d->btf->strs_deduped = true; d->btf->strs_deduped = true;
return 0; return 0;
err_out: err_out:
free(d->strs_data); strset__free(d->strs_set);
hashmap__free(d->strs_hash); d->strs_set = NULL;
d->strs_data = d->strs_hash = NULL;
d->strs_len = d->strs_cap = 0;
/* restore strings pointer for existing d->btf->strs_hash back */
d->btf->strs_data_ptr = &d->strs_data;
return err; return err;
} }

176
tools/lib/bpf/strset.c Normal file
View file

@ -0,0 +1,176 @@
// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
/* Copyright (c) 2021 Facebook */
#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <linux/err.h>
#include "hashmap.h"
#include "libbpf_internal.h"
#include "strset.h"
struct strset {
void *strs_data;
size_t strs_data_len;
size_t strs_data_cap;
size_t strs_data_max_len;
/* lookup index for each unique string in strings set */
struct hashmap *strs_hash;
};
static size_t strset_hash_fn(const void *key, void *ctx)
{
const struct strset *s = ctx;
const char *str = s->strs_data + (long)key;
return str_hash(str);
}
static bool strset_equal_fn(const void *key1, const void *key2, void *ctx)
{
const struct strset *s = ctx;
const char *str1 = s->strs_data + (long)key1;
const char *str2 = s->strs_data + (long)key2;
return strcmp(str1, str2) == 0;
}
struct strset *strset__new(size_t max_data_sz, const char *init_data, size_t init_data_sz)
{
struct strset *set = calloc(1, sizeof(*set));
struct hashmap *hash;
int err = -ENOMEM;
if (!set)
return ERR_PTR(-ENOMEM);
hash = hashmap__new(strset_hash_fn, strset_equal_fn, set);
if (IS_ERR(hash))
goto err_out;
set->strs_data_max_len = max_data_sz;
set->strs_hash = hash;
if (init_data) {
long off;
set->strs_data = malloc(init_data_sz);
if (!set->strs_data)
goto err_out;
memcpy(set->strs_data, init_data, init_data_sz);
set->strs_data_len = init_data_sz;
set->strs_data_cap = init_data_sz;
for (off = 0; off < set->strs_data_len; off += strlen(set->strs_data + off) + 1) {
/* hashmap__add() returns EEXIST if string with the same
* content already is in the hash map
*/
err = hashmap__add(hash, (void *)off, (void *)off);
if (err == -EEXIST)
continue; /* duplicate */
if (err)
goto err_out;
}
}
return set;
err_out:
strset__free(set);
return ERR_PTR(err);
}
void strset__free(struct strset *set)
{
if (IS_ERR_OR_NULL(set))
return;
hashmap__free(set->strs_hash);
free(set->strs_data);
}
size_t strset__data_size(const struct strset *set)
{
return set->strs_data_len;
}
const char *strset__data(const struct strset *set)
{
return set->strs_data;
}
static void *strset_add_str_mem(struct strset *set, size_t add_sz)
{
return libbpf_add_mem(&set->strs_data, &set->strs_data_cap, 1,
set->strs_data_len, set->strs_data_max_len, add_sz);
}
/* Find string offset that corresponds to a given string *s*.
* Returns:
* - >0 offset into string data, if string is found;
* - -ENOENT, if string is not in the string data;
* - <0, on any other error.
*/
int strset__find_str(struct strset *set, const char *s)
{
long old_off, new_off, len;
void *p;
/* see strset__add_str() for why we do this */
len = strlen(s) + 1;
p = strset_add_str_mem(set, len);
if (!p)
return -ENOMEM;
new_off = set->strs_data_len;
memcpy(p, s, len);
if (hashmap__find(set->strs_hash, (void *)new_off, (void **)&old_off))
return old_off;
return -ENOENT;
}
/* Add a string s to the string data. If the string already exists, return its
* offset within string data.
* Returns:
* - > 0 offset into string data, on success;
* - < 0, on error.
*/
int strset__add_str(struct strset *set, const char *s)
{
long old_off, new_off, len;
void *p;
int err;
/* Hashmap keys are always offsets within set->strs_data, so to even
* look up some string from the "outside", we need to first append it
* at the end, so that it can be addressed with an offset. Luckily,
* until set->strs_data_len is incremented, that string is just a piece
* of garbage for the rest of the code, so no harm, no foul. On the
* other hand, if the string is unique, it's already appended and
* ready to be used, only a simple set->strs_data_len increment away.
*/
len = strlen(s) + 1;
p = strset_add_str_mem(set, len);
if (!p)
return -ENOMEM;
new_off = set->strs_data_len;
memcpy(p, s, len);
/* Now attempt to add the string, but only if the string with the same
* contents doesn't exist already (HASHMAP_ADD strategy). If such
* string exists, we'll get its offset in old_off (that's old_key).
*/
err = hashmap__insert(set->strs_hash, (void *)new_off, (void *)new_off,
HASHMAP_ADD, (const void **)&old_off, NULL);
if (err == -EEXIST)
return old_off; /* duplicated string, return existing offset */
if (err)
return err;
set->strs_data_len += len; /* new unique string, adjust data length */
return new_off;
}

21
tools/lib/bpf/strset.h Normal file
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/* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
/* Copyright (c) 2021 Facebook */
#ifndef __LIBBPF_STRSET_H
#define __LIBBPF_STRSET_H
#include <stdbool.h>
#include <stddef.h>
struct strset;
struct strset *strset__new(size_t max_data_sz, const char *init_data, size_t init_data_sz);
void strset__free(struct strset *set);
const char *strset__data(const struct strset *set);
size_t strset__data_size(const struct strset *set);
int strset__find_str(struct strset *set, const char *s);
int strset__add_str(struct strset *set, const char *s);
#endif /* __LIBBPF_STRSET_H */