Merge branch 'btf2c-converter'

Andrii Nakryiko says:

====================
This patch set adds BTF-to-C dumping APIs to libbpf, allowing to output
a subset of BTF types as a compilable C type definitions. This is useful by
itself, as raw BTF output is not easy to inspect and comprehend. But it's also
a big part of BPF CO-RE (compile once - run everywhere) initiative aimed at
allowing to write relocatable BPF programs, that won't require on-the-host
kernel headers (and would be able to inspect internal kernel structures, not
exposed through kernel headers).

This patch set consists of three groups of patches and one pre-patch, with the
BTF-to-C dumper API depending on the first two groups.

Pre-patch #1 fixes issue with libbpf_internal.h.

btf__parse_elf() API patches:
- patch #2 adds btf__parse_elf() API to libbpf, allowing to load BTF and/or
  BTF.ext from ELF file;
- patch #3 utilizies btf__parse_elf() from bpftool for `btf dump file` command;
- patch #4 switches test_btf.c to use btf__parse_elf() to check for presence
  of BTF data in object file.

libbpf's internal hashmap patches:
- patch #5 adds resizeable non-thread safe generic hashmap to libbpf;
- patch #6 adds tests for that hashmap;
- patch #7 migrates btf_dedup()'s dedup_table to use hashmap w/ APPEND.

BTF-to-C dumper API patches:
- patch #8 adds btf_dump APIs with all the logic for laying out type
  definitions in correct order and emitting C syntax for them;
- patch #9 adds lots of tests for common and quirky parts of C type system;
- patch #10 adds support for C-syntax btf dumping to bpftool;
- patch #11 updates bpftool documentation to mention C-syntax dump option;
- patch #12 update bash-completion for btf dump sub-command.

v2->v3:
- fix bpftool-btf.rst formatting (Quentin);
- simplify bash autocompletion script (Quentin);
- better error message in btf dump (Quentin);

v1->v2:
- removed unuseful file header (Jakub);
- removed inlines in .c (Jakub);
- added 'format {c|raw}' keyword/option (Jakub);
- re-use i var for iteration in btf_dump_c() (Jakub);
- bumped libbpf version to 0.0.4;

v0->v1:
- fix bug in hashmap__for_each_bucket_entry() not handling empty hashmap;
- removed `btf dump`-specific libbpf logging hook up (Quentin has more generic
  patchset);
- change btf__parse_elf() to always load .BTF and return it as a result, with
  .BTF.ext being optional and returned through struct btf_ext** arg (Alexei);
- endianness check to use __BYTE_ORDER__ (Alexei);
- bool:1 to __u8:1 in type_aux_state (Alexei);
- added HASHMAP_APPEND strategy to hashmap, changed
  hashmap__for_each_key_entry() to also check for key equality during
  iteration (multimap iteration for key);
- added new tests for empty hashmap and hashmap as a multimap;
- tried to clarify weak/strong dependency ordering comments (Alexei)
- btf dump test's expected output - support better commenting aproach (Alexei);
- added bash-completion for a new "c" option (Alexei).
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/bpf/bpftool/Documentation/bpftool-btf.rst

@@ -19,10 +19,11 @@ SYNOPSIS
 BTF COMMANDS
 =============
 
-|	**bpftool** **btf dump** *BTF_SRC*
+|	**bpftool** **btf dump** *BTF_SRC* [**format** *FORMAT*]
 |	**bpftool** **btf help**
 |
 |	*BTF_SRC* := { **id** *BTF_ID* | **prog** *PROG* | **map** *MAP* [{**key** | **value** | **kv** | **all**}] | **file** *FILE* }
+|	*FORMAT* := { **raw** | **c** }
 |	*MAP* := { **id** *MAP_ID* | **pinned** *FILE* }
 |	*PROG* := { **id** *PROG_ID* | **pinned** *FILE* | **tag** *PROG_TAG* }
 
@@ -31,23 +32,27 @@ DESCRIPTION
 	**bpftool btf dump** *BTF_SRC*
 		  Dump BTF entries from a given *BTF_SRC*.
 
-                  When **id** is specified, BTF object with that ID will be
-                  loaded and all its BTF types emitted.
+		  When **id** is specified, BTF object with that ID will be
+		  loaded and all its BTF types emitted.
 
-                  When **map** is provided, it's expected that map has
-                  associated BTF object with BTF types describing key and
-                  value. It's possible to select whether to dump only BTF
-                  type(s) associated with key (**key**), value (**value**),
-                  both key and value (**kv**), or all BTF types present in
-                  associated BTF object (**all**). If not specified, **kv**
-                  is assumed.
+		  When **map** is provided, it's expected that map has
+		  associated BTF object with BTF types describing key and
+		  value. It's possible to select whether to dump only BTF
+		  type(s) associated with key (**key**), value (**value**),
+		  both key and value (**kv**), or all BTF types present in
+		  associated BTF object (**all**). If not specified, **kv**
+		  is assumed.
 
-                  When **prog** is provided, it's expected that program has
-                  associated BTF object with BTF types.
+		  When **prog** is provided, it's expected that program has
+		  associated BTF object with BTF types.
 
-                  When specifying *FILE*, an ELF file is expected, containing
-                  .BTF section with well-defined BTF binary format data,
-                  typically produced by clang or pahole.
+		  When specifying *FILE*, an ELF file is expected, containing
+		  .BTF section with well-defined BTF binary format data,
+		  typically produced by clang or pahole.
+
+		  **format** option can be used to override default (raw)
+		  output format. Raw (**raw**) or C-syntax (**c**) output
+		  formats are supported.
 
 	**bpftool btf help**
 		  Print short help message.

tools/bpf/bpftool/bash-completion/bpftool

@@ -638,11 +638,24 @@ _bpftool()
                             esac
                             return 0
                             ;;
+                        format)
+                            COMPREPLY=( $( compgen -W "c raw" -- "$cur" ) )
+                            ;;
                         *)
-                            if [[ $cword == 6 ]] && [[ ${words[3]} == "map" ]]; then
-                                 COMPREPLY+=( $( compgen -W 'key value kv all' -- \
-                                     "$cur" ) )
-                            fi
+                            # emit extra options
+                            case ${words[3]} in
+                                id|file)
+                                    _bpftool_once_attr 'format'
+                                    ;;
+                                map|prog)
+                                    if [[ ${words[3]} == "map" ]] && [[ $cword == 6 ]]; then
+                                        COMPREPLY+=( $( compgen -W "key value kv all" -- "$cur" ) )
+                                    fi
+                                    _bpftool_once_attr 'format'
+                                    ;;
+                                *)
+                                    ;;
+                            esac
                             return 0
                             ;;
                     esac

tools/bpf/bpftool/btf.c

@@ -8,8 +8,8 @@
 #include <stdio.h>
 #include <string.h>
 #include <unistd.h>
-#include <gelf.h>
 #include <bpf.h>
+#include <libbpf.h>
 #include <linux/btf.h>
 
 #include "btf.h"
@@ -340,109 +340,40 @@ static int dump_btf_raw(const struct btf *btf,
 	return 0;
 }
 
-static bool check_btf_endianness(GElf_Ehdr *ehdr)
+static void __printf(2, 0) btf_dump_printf(void *ctx,
+					   const char *fmt, va_list args)
 {
-	static unsigned int const endian = 1;
-
-	switch (ehdr->e_ident[EI_DATA]) {
-	case ELFDATA2LSB:
-		return *(unsigned char const *)&endian == 1;
-	case ELFDATA2MSB:
-		return *(unsigned char const *)&endian == 0;
-	default:
-		return 0;
-	}
+	vfprintf(stdout, fmt, args);
 }
 
-static int btf_load_from_elf(const char *path, struct btf **btf)
+static int dump_btf_c(const struct btf *btf,
+		      __u32 *root_type_ids, int root_type_cnt)
 {
-	int err = -1, fd = -1, idx = 0;
-	Elf_Data *btf_data = NULL;
-	Elf_Scn *scn = NULL;
-	Elf *elf = NULL;
-	GElf_Ehdr ehdr;
+	struct btf_dump *d;
+	int err = 0, i;
 
-	if (elf_version(EV_CURRENT) == EV_NONE) {
-		p_err("failed to init libelf for %s", path);
-		return -1;
-	}
+	d = btf_dump__new(btf, NULL, NULL, btf_dump_printf);
+	if (IS_ERR(d))
+		return PTR_ERR(d);
 
-	fd = open(path, O_RDONLY);
-	if (fd < 0) {
-		p_err("failed to open %s: %s", path, strerror(errno));
-		return -1;
-	}
-
-	elf = elf_begin(fd, ELF_C_READ, NULL);
-	if (!elf) {
-		p_err("failed to open %s as ELF file", path);
-		goto done;
-	}
-	if (!gelf_getehdr(elf, &ehdr)) {
-		p_err("failed to get EHDR from %s", path);
-		goto done;
-	}
-	if (!check_btf_endianness(&ehdr)) {
-		p_err("non-native ELF endianness is not supported");
-		goto done;
-	}
-	if (!elf_rawdata(elf_getscn(elf, ehdr.e_shstrndx), NULL)) {
-		p_err("failed to get e_shstrndx from %s\n", path);
-		goto done;
-	}
-
-	while ((scn = elf_nextscn(elf, scn)) != NULL) {
-		GElf_Shdr sh;
-		char *name;
+	if (root_type_cnt) {
+		for (i = 0; i < root_type_cnt; i++) {
+			err = btf_dump__dump_type(d, root_type_ids[i]);
+			if (err)
+				goto done;
+		}
+	} else {
+		int cnt = btf__get_nr_types(btf);
 
-		idx++;
-		if (gelf_getshdr(scn, &sh) != &sh) {
-			p_err("failed to get section(%d) header from %s",
-			      idx, path);
-			goto done;
-		}
-		name = elf_strptr(elf, ehdr.e_shstrndx, sh.sh_name);
-		if (!name) {
-			p_err("failed to get section(%d) name from %s",
-			      idx, path);
-			goto done;
-		}
-		if (strcmp(name, BTF_ELF_SEC) == 0) {
-			btf_data = elf_getdata(scn, 0);
-			if (!btf_data) {
-				p_err("failed to get section(%d, %s) data from %s",
-				      idx, name, path);
+		for (i = 1; i <= cnt; i++) {
+			err = btf_dump__dump_type(d, i);
+			if (err)
 				goto done;
-			}
-			break;
 		}
 	}
 
-	if (!btf_data) {
-		p_err("%s ELF section not found in %s", BTF_ELF_SEC, path);
-		goto done;
-	}
-
-	*btf = btf__new(btf_data->d_buf, btf_data->d_size);
-	if (IS_ERR(*btf)) {
-		err = PTR_ERR(*btf);
-		*btf = NULL;
-		p_err("failed to load BTF data from %s: %s",
-		      path, strerror(err));
-		goto done;
-	}
-
-	err = 0;
 done:
-	if (err) {
-		if (*btf) {
-			btf__free(*btf);
-			*btf = NULL;
-		}
-	}
-	if (elf)
-		elf_end(elf);
-	close(fd);
+	btf_dump__free(d);
 	return err;
 }
 
@@ -451,6 +382,7 @@ static int do_dump(int argc, char **argv)
 	struct btf *btf = NULL;
 	__u32 root_type_ids[2];
 	int root_type_cnt = 0;
+	bool dump_c = false;
 	__u32 btf_id = -1;
 	const char *src;
 	int fd = -1;
@@ -522,9 +454,14 @@ static int do_dump(int argc, char **argv)
 		}
 		NEXT_ARG();
 	} else if (is_prefix(src, "file")) {
-		err = btf_load_from_elf(*argv, &btf);
-		if (err)
+		btf = btf__parse_elf(*argv, NULL);
+		if (IS_ERR(btf)) {
+			err = PTR_ERR(btf);
+			btf = NULL;
+			p_err("failed to load BTF from %s: %s", 
+			      *argv, strerror(err));
 			goto done;
+		}
 		NEXT_ARG();
 	} else {
 		err = -1;
@@ -532,6 +469,29 @@ static int do_dump(int argc, char **argv)
 		goto done;
 	}
 
+	while (argc) {
+		if (is_prefix(*argv, "format")) {
+			NEXT_ARG();
+			if (argc < 1) {
+				p_err("expecting value for 'format' option\n");
+				goto done;
+			}
+			if (strcmp(*argv, "c") == 0) {
+				dump_c = true;
+			} else if (strcmp(*argv, "raw") == 0) {
+				dump_c = false;
+			} else {
+				p_err("unrecognized format specifier: '%s', possible values: raw, c",
+				      *argv);
+				goto done;
+			}
+			NEXT_ARG();
+		} else {
+			p_err("unrecognized option: '%s'", *argv);
+			goto done;
+		}
+	}
+
 	if (!btf) {
 		err = btf__get_from_id(btf_id, &btf);
 		if (err) {
@@ -545,7 +505,16 @@ static int do_dump(int argc, char **argv)
 		}
 	}
 
-	dump_btf_raw(btf, root_type_ids, root_type_cnt);
+	if (dump_c) {
+		if (json_output) {
+			p_err("JSON output for C-syntax dump is not supported");
+			err = -ENOTSUP;
+			goto done;
+		}
+		err = dump_btf_c(btf, root_type_ids, root_type_cnt);
+	} else {
+		err = dump_btf_raw(btf, root_type_ids, root_type_cnt);
+	}
 
 done:
 	close(fd);
@@ -561,10 +530,11 @@ static int do_help(int argc, char **argv)
 	}
 
 	fprintf(stderr,
-		"Usage: %s btf dump BTF_SRC\n"
+		"Usage: %s btf dump BTF_SRC [format FORMAT]\n"
 		"       %s btf help\n"
 		"\n"
 		"       BTF_SRC := { id BTF_ID | prog PROG | map MAP [{key | value | kv | all}] | file FILE }\n"
+		"       FORMAT  := { raw | c }\n"
 		"       " HELP_SPEC_MAP "\n"
 		"       " HELP_SPEC_PROGRAM "\n"
 		"       " HELP_SPEC_OPTIONS "\n"

tools/lib/bpf/Build

@@ -1 +1,3 @@
-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
+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 \
+	    btf_dump.o

tools/lib/bpf/btf.h

@@ -4,6 +4,7 @@
 #ifndef __LIBBPF_BTF_H
 #define __LIBBPF_BTF_H
 
+#include <stdarg.h>
 #include <linux/types.h>
 
 #ifdef __cplusplus
@@ -59,6 +60,8 @@ struct btf_ext_header {
 
 LIBBPF_API void btf__free(struct btf *btf);
 LIBBPF_API struct btf *btf__new(__u8 *data, __u32 size);
+LIBBPF_API struct btf *btf__parse_elf(const char *path,
+				      struct btf_ext **btf_ext);
 LIBBPF_API int btf__finalize_data(struct bpf_object *obj, struct btf *btf);
 LIBBPF_API int btf__load(struct btf *btf);
 LIBBPF_API __s32 btf__find_by_name(const struct btf *btf,
@@ -100,6 +103,22 @@ struct btf_dedup_opts {
 LIBBPF_API int btf__dedup(struct btf *btf, struct btf_ext *btf_ext,
 			  const struct btf_dedup_opts *opts);
 
+struct btf_dump;
+
+struct btf_dump_opts {
+	void *ctx;
+};
+
+typedef void (*btf_dump_printf_fn_t)(void *ctx, const char *fmt, va_list args);
+
+LIBBPF_API struct btf_dump *btf_dump__new(const struct btf *btf,
+					  const struct btf_ext *btf_ext,
+					  const struct btf_dump_opts *opts,
+					  btf_dump_printf_fn_t printf_fn);
+LIBBPF_API void btf_dump__free(struct btf_dump *d);
+
+LIBBPF_API int btf_dump__dump_type(struct btf_dump *d, __u32 id);
+
 #ifdef __cplusplus
 } /* extern "C" */
 #endif

tools/lib/bpf/hashmap.c

@@ -0,0 +1,229 @@
+// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
+
+/*
+ * Generic non-thread safe hash map implementation.
+ *
+ * Copyright (c) 2019 Facebook
+ */
+#include <stdint.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <errno.h>
+#include <linux/err.h>
+#include "hashmap.h"
+
+/* start with 4 buckets */
+#define HASHMAP_MIN_CAP_BITS 2
+
+static void hashmap_add_entry(struct hashmap_entry **pprev,
+			      struct hashmap_entry *entry)
+{
+	entry->next = *pprev;
+	*pprev = entry;
+}
+
+static void hashmap_del_entry(struct hashmap_entry **pprev,
+			      struct hashmap_entry *entry)
+{
+	*pprev = entry->next;
+	entry->next = NULL;
+}
+
+void hashmap__init(struct hashmap *map, hashmap_hash_fn hash_fn,
+		   hashmap_equal_fn equal_fn, void *ctx)
+{
+	map->hash_fn = hash_fn;
+	map->equal_fn = equal_fn;
+	map->ctx = ctx;
+
+	map->buckets = NULL;
+	map->cap = 0;
+	map->cap_bits = 0;
+	map->sz = 0;
+}
+
+struct hashmap *hashmap__new(hashmap_hash_fn hash_fn,
+			     hashmap_equal_fn equal_fn,
+			     void *ctx)
+{
+	struct hashmap *map = malloc(sizeof(struct hashmap));
+
+	if (!map)
+		return ERR_PTR(-ENOMEM);
+	hashmap__init(map, hash_fn, equal_fn, ctx);
+	return map;
+}
+
+void hashmap__clear(struct hashmap *map)
+{
+	free(map->buckets);
+	map->cap = map->cap_bits = map->sz = 0;
+}
+
+void hashmap__free(struct hashmap *map)
+{
+	if (!map)
+		return;
+
+	hashmap__clear(map);
+	free(map);
+}
+
+size_t hashmap__size(const struct hashmap *map)
+{
+	return map->sz;
+}
+
+size_t hashmap__capacity(const struct hashmap *map)
+{
+	return map->cap;
+}
+
+static bool hashmap_needs_to_grow(struct hashmap *map)
+{
+	/* grow if empty or more than 75% filled */
+	return (map->cap == 0) || ((map->sz + 1) * 4 / 3 > map->cap);
+}
+
+static int hashmap_grow(struct hashmap *map)
+{
+	struct hashmap_entry **new_buckets;
+	struct hashmap_entry *cur, *tmp;
+	size_t new_cap_bits, new_cap;
+	size_t h;
+	int bkt;
+
+	new_cap_bits = map->cap_bits + 1;
+	if (new_cap_bits < HASHMAP_MIN_CAP_BITS)
+		new_cap_bits = HASHMAP_MIN_CAP_BITS;
+
+	new_cap = 1UL << new_cap_bits;
+	new_buckets = calloc(new_cap, sizeof(new_buckets[0]));
+	if (!new_buckets)
+		return -ENOMEM;
+
+	hashmap__for_each_entry_safe(map, cur, tmp, bkt) {
+		h = hash_bits(map->hash_fn(cur->key, map->ctx), new_cap_bits);
+		hashmap_add_entry(&new_buckets[h], cur);
+	}
+
+	map->cap = new_cap;
+	map->cap_bits = new_cap_bits;
+	free(map->buckets);
+	map->buckets = new_buckets;
+
+	return 0;
+}
+
+static bool hashmap_find_entry(const struct hashmap *map,
+			       const void *key, size_t hash,
+			       struct hashmap_entry ***pprev,
+			       struct hashmap_entry **entry)
+{
+	struct hashmap_entry *cur, **prev_ptr;
+
+	if (!map->buckets)
+		return false;
+
+	for (prev_ptr = &map->buckets[hash], cur = *prev_ptr;
+	     cur;
+	     prev_ptr = &cur->next, cur = cur->next) {
+		if (map->equal_fn(cur->key, key, map->ctx)) {
+			if (pprev)
+				*pprev = prev_ptr;
+			*entry = cur;
+			return true;
+		}
+	}
+
+	return false;
+}
+
+int hashmap__insert(struct hashmap *map, const void *key, void *value,
+		    enum hashmap_insert_strategy strategy,
+		    const void **old_key, void **old_value)
+{
+	struct hashmap_entry *entry;
+	size_t h;
+	int err;
+
+	if (old_key)
+		*old_key = NULL;
+	if (old_value)
+		*old_value = NULL;
+
+	h = hash_bits(map->hash_fn(key, map->ctx), map->cap_bits);
+	if (strategy != HASHMAP_APPEND &&
+	    hashmap_find_entry(map, key, h, NULL, &entry)) {
+		if (old_key)
+			*old_key = entry->key;
+		if (old_value)
+			*old_value = entry->value;
+
+		if (strategy == HASHMAP_SET || strategy == HASHMAP_UPDATE) {
+			entry->key = key;
+			entry->value = value;
+			return 0;
+		} else if (strategy == HASHMAP_ADD) {
+			return -EEXIST;
+		}
+	}
+
+	if (strategy == HASHMAP_UPDATE)
+		return -ENOENT;
+
+	if (hashmap_needs_to_grow(map)) {
+		err = hashmap_grow(map);
+		if (err)
+			return err;
+		h = hash_bits(map->hash_fn(key, map->ctx), map->cap_bits);
+	}
+
+	entry = malloc(sizeof(struct hashmap_entry));
+	if (!entry)
+		return -ENOMEM;
+
+	entry->key = key;
+	entry->value = value;
+	hashmap_add_entry(&map->buckets[h], entry);
+	map->sz++;
+
+	return 0;
+}
+
+bool hashmap__find(const struct hashmap *map, const void *key, void **value)
+{
+	struct hashmap_entry *entry;
+	size_t h;
+
+	h = hash_bits(map->hash_fn(key, map->ctx), map->cap_bits);
+	if (!hashmap_find_entry(map, key, h, NULL, &entry))
+		return false;
+
+	if (value)
+		*value = entry->value;
+	return true;
+}
+
+bool hashmap__delete(struct hashmap *map, const void *key,
+		     const void **old_key, void **old_value)
+{
+	struct hashmap_entry **pprev, *entry;
+	size_t h;
+
+	h = hash_bits(map->hash_fn(key, map->ctx), map->cap_bits);
+	if (!hashmap_find_entry(map, key, h, &pprev, &entry))
+		return false;
+
+	if (old_key)
+		*old_key = entry->key;
+	if (old_value)
+		*old_value = entry->value;
+
+	hashmap_del_entry(pprev, entry);
+	free(entry);
+	map->sz--;
+
+	return true;
+}
+

tools/lib/bpf/hashmap.h

@@ -0,0 +1,173 @@
+/* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
+
+/*
+ * Generic non-thread safe hash map implementation.
+ *
+ * Copyright (c) 2019 Facebook
+ */
+#ifndef __LIBBPF_HASHMAP_H
+#define __LIBBPF_HASHMAP_H
+
+#include <stdbool.h>
+#include <stddef.h>
+#include "libbpf_internal.h"
+
+static inline size_t hash_bits(size_t h, int bits)
+{
+	/* shuffle bits and return requested number of upper bits */
+	return (h * 11400714819323198485llu) >> (__WORDSIZE - bits);
+}
+
+typedef size_t (*hashmap_hash_fn)(const void *key, void *ctx);
+typedef bool (*hashmap_equal_fn)(const void *key1, const void *key2, void *ctx);
+
+struct hashmap_entry {
+	const void *key;
+	void *value;
+	struct hashmap_entry *next;
+};
+
+struct hashmap {
+	hashmap_hash_fn hash_fn;
+	hashmap_equal_fn equal_fn;
+	void *ctx;
+
+	struct hashmap_entry **buckets;
+	size_t cap;
+	size_t cap_bits;
+	size_t sz;
+};
+
+#define HASHMAP_INIT(hash_fn, equal_fn, ctx) {	\
+	.hash_fn = (hash_fn),			\
+	.equal_fn = (equal_fn),			\
+	.ctx = (ctx),				\
+	.buckets = NULL,			\
+	.cap = 0,				\
+	.cap_bits = 0,				\
+	.sz = 0,				\
+}
+
+void hashmap__init(struct hashmap *map, hashmap_hash_fn hash_fn,
+		   hashmap_equal_fn equal_fn, void *ctx);
+struct hashmap *hashmap__new(hashmap_hash_fn hash_fn,
+			     hashmap_equal_fn equal_fn,
+			     void *ctx);
+void hashmap__clear(struct hashmap *map);
+void hashmap__free(struct hashmap *map);
+
+size_t hashmap__size(const struct hashmap *map);
+size_t hashmap__capacity(const struct hashmap *map);
+
+/*
+ * Hashmap insertion strategy:
+ * - HASHMAP_ADD - only add key/value if key doesn't exist yet;
+ * - HASHMAP_SET - add key/value pair if key doesn't exist yet; otherwise,
+ *   update value;
+ * - HASHMAP_UPDATE - update value, if key already exists; otherwise, do
+ *   nothing and return -ENOENT;
+ * - HASHMAP_APPEND - always add key/value pair, even if key already exists.
+ *   This turns hashmap into a multimap by allowing multiple values to be
+ *   associated with the same key. Most useful read API for such hashmap is
+ *   hashmap__for_each_key_entry() iteration. If hashmap__find() is still
+ *   used, it will return last inserted key/value entry (first in a bucket
+ *   chain).
+ */
+enum hashmap_insert_strategy {
+	HASHMAP_ADD,
+	HASHMAP_SET,
+	HASHMAP_UPDATE,
+	HASHMAP_APPEND,
+};
+
+/*
+ * hashmap__insert() adds key/value entry w/ various semantics, depending on
+ * provided strategy value. If a given key/value pair replaced already
+ * existing key/value pair, both old key and old value will be returned
+ * through old_key and old_value to allow calling code do proper memory
+ * management.
+ */
+int hashmap__insert(struct hashmap *map, const void *key, void *value,
+		    enum hashmap_insert_strategy strategy,
+		    const void **old_key, void **old_value);
+
+static inline int hashmap__add(struct hashmap *map,
+			       const void *key, void *value)
+{
+	return hashmap__insert(map, key, value, HASHMAP_ADD, NULL, NULL);
+}
+
+static inline int hashmap__set(struct hashmap *map,
+			       const void *key, void *value,
+			       const void **old_key, void **old_value)
+{
+	return hashmap__insert(map, key, value, HASHMAP_SET,
+			       old_key, old_value);
+}
+
+static inline int hashmap__update(struct hashmap *map,
+				  const void *key, void *value,
+				  const void **old_key, void **old_value)
+{
+	return hashmap__insert(map, key, value, HASHMAP_UPDATE,
+			       old_key, old_value);
+}
+
+static inline int hashmap__append(struct hashmap *map,
+				  const void *key, void *value)
+{
+	return hashmap__insert(map, key, value, HASHMAP_APPEND, NULL, NULL);
+}
+
+bool hashmap__delete(struct hashmap *map, const void *key,
+		     const void **old_key, void **old_value);
+
+bool hashmap__find(const struct hashmap *map, const void *key, void **value);
+
+/*
+ * hashmap__for_each_entry - iterate over all entries in hashmap
+ * @map: hashmap to iterate
+ * @cur: struct hashmap_entry * used as a loop cursor
+ * @bkt: integer used as a bucket loop cursor
+ */
+#define hashmap__for_each_entry(map, cur, bkt)				    \
+	for (bkt = 0; bkt < map->cap; bkt++)				    \
+		for (cur = map->buckets[bkt]; cur; cur = cur->next)
+
+/*
+ * hashmap__for_each_entry_safe - iterate over all entries in hashmap, safe
+ * against removals
+ * @map: hashmap to iterate
+ * @cur: struct hashmap_entry * used as a loop cursor
+ * @tmp: struct hashmap_entry * used as a temporary next cursor storage
+ * @bkt: integer used as a bucket loop cursor
+ */
+#define hashmap__for_each_entry_safe(map, cur, tmp, bkt)		    \
+	for (bkt = 0; bkt < map->cap; bkt++)				    \
+		for (cur = map->buckets[bkt];				    \
+		     cur && ({tmp = cur->next; true; });		    \
+		     cur = tmp)
+
+/*
+ * hashmap__for_each_key_entry - iterate over entries associated with given key
+ * @map: hashmap to iterate
+ * @cur: struct hashmap_entry * used as a loop cursor
+ * @key: key to iterate entries for
+ */
+#define hashmap__for_each_key_entry(map, cur, _key)			    \
+	for (cur = ({ size_t bkt = hash_bits(map->hash_fn((_key), map->ctx),\
+					     map->cap_bits);		    \
+		     map->buckets ? map->buckets[bkt] : NULL; });	    \
+	     cur;							    \
+	     cur = cur->next)						    \
+		if (map->equal_fn(cur->key, (_key), map->ctx))
+
+#define hashmap__for_each_key_entry_safe(map, cur, tmp, _key)		    \
+	for (cur = ({ size_t bkt = hash_bits(map->hash_fn((_key), map->ctx),\
+					     map->cap_bits);		    \
+		     cur = map->buckets ? map->buckets[bkt] : NULL; });	    \
+	     cur && ({ tmp = cur->next; true; });			    \
+	     cur = tmp)							    \
+		if (map->equal_fn(cur->key, (_key), map->ctx))
+
+#endif /* __LIBBPF_HASHMAP_H */

tools/lib/bpf/libbpf.map

@@ -164,3 +164,11 @@ LIBBPF_0.0.3 {
 		bpf_map_freeze;
 		btf__finalize_data;
 } LIBBPF_0.0.2;
+
+LIBBPF_0.0.4 {
+	global:
+		btf_dump__dump_type;
+		btf_dump__free;
+		btf_dump__new;
+		btf__parse_elf;
+} LIBBPF_0.0.3;

tools/lib/bpf/libbpf_internal.h

@@ -9,6 +9,8 @@
 #ifndef __LIBBPF_LIBBPF_INTERNAL_H
 #define __LIBBPF_LIBBPF_INTERNAL_H
 
+#include "libbpf.h"
+
 #define BTF_INFO_ENC(kind, kind_flag, vlen) \
 	((!!(kind_flag) << 31) | ((kind) << 24) | ((vlen) & BTF_MAX_VLEN))
 #define BTF_TYPE_ENC(name, info, size_or_type) (name), (info), (size_or_type)

tools/testing/selftests/bpf/.gitignore

@@ -35,3 +35,5 @@ test_sysctl
 alu32
 libbpf.pc
 libbpf.so.*
+test_hashmap
+test_btf_dump

tools/testing/selftests/bpf/Makefile

@@ -23,7 +23,8 @@ TEST_GEN_PROGS = test_verifier test_tag test_maps test_lru_map test_lpm_map test
 	test_align test_verifier_log test_dev_cgroup test_tcpbpf_user \
 	test_sock test_btf test_sockmap test_lirc_mode2_user get_cgroup_id_user \
 	test_socket_cookie test_cgroup_storage test_select_reuseport test_section_names \
-	test_netcnt test_tcpnotify_user test_sock_fields test_sysctl
+	test_netcnt test_tcpnotify_user test_sock_fields test_sysctl test_hashmap \
+	test_btf_dump
 
 BPF_OBJ_FILES = $(patsubst %.c,%.o, $(notdir $(wildcard progs/*.c)))
 TEST_GEN_FILES = $(BPF_OBJ_FILES)

tools/testing/selftests/bpf/progs/btf_dump_test_case_bitfields.c

@@ -0,0 +1,92 @@
+// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
+
+/*
+ * BTF-to-C dumper tests for bitfield.
+ *
+ * Copyright (c) 2019 Facebook
+ */
+#include <stdbool.h>
+
+/* ----- START-EXPECTED-OUTPUT ----- */
+/*
+ *struct bitfields_only_mixed_types {
+ *	int a: 3;
+ *	long int b: 2;
+ *	_Bool c: 1;
+ *	enum {
+ *		A = 0,
+ *		B = 1,
+ *	} d: 1;
+ *	short e: 5;
+ *	int: 20;
+ *	unsigned int f: 30;
+ *};
+ *
+ */
+/* ------ END-EXPECTED-OUTPUT ------ */
+
+struct bitfields_only_mixed_types {
+	int a: 3;
+	long int b: 2;
+	bool c: 1; /* it's really a _Bool type */
+	enum {
+		A, /* A = 0, dumper is very explicit */
+		B, /* B = 1, same */
+	} d: 1;
+	short e: 5;
+	/* 20-bit padding here */
+	unsigned f: 30; /* this gets aligned on 4-byte boundary */
+};
+
+/* ----- START-EXPECTED-OUTPUT ----- */
+/*
+ *struct bitfield_mixed_with_others {
+ *	char: 4;
+ *	int a: 4;
+ *	short b;
+ *	long int c;
+ *	long int d: 8;
+ *	int e;
+ *	int f;
+ *};
+ *
+ */
+/* ------ END-EXPECTED-OUTPUT ------ */
+struct bitfield_mixed_with_others {
+	long: 4; /* char is enough as a backing field */
+	int a: 4;
+	/* 8-bit implicit padding */
+	short b; /* combined with previous bitfield */
+	/* 4 more bytes of implicit padding */
+	long c;
+	long d: 8;
+	/* 24 bits implicit padding */
+	int e; /* combined with previous bitfield */
+	int f;
+	/* 4 bytes of padding */
+};
+
+/* ----- START-EXPECTED-OUTPUT ----- */
+/*
+ *struct bitfield_flushed {
+ *	int a: 4;
+ *	long: 60;
+ *	long int b: 16;
+ *};
+ *
+ */
+/* ------ END-EXPECTED-OUTPUT ------ */
+struct bitfield_flushed {
+	int a: 4;
+	long: 0; /* flush until next natural alignment boundary */
+	long b: 16;
+};
+
+int f(struct {
+	struct bitfields_only_mixed_types _1;
+	struct bitfield_mixed_with_others _2;
+	struct bitfield_flushed _3;
+} *_)
+{
+	return 0;
+}

tools/testing/selftests/bpf/progs/btf_dump_test_case_multidim.c

@@ -0,0 +1,35 @@
+// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
+
+/*
+ * BTF-to-C dumper test for multi-dimensional array output.
+ *
+ * Copyright (c) 2019 Facebook
+ */
+/* ----- START-EXPECTED-OUTPUT ----- */
+typedef int arr_t[2];
+
+typedef int multiarr_t[3][4][5];
+
+typedef int *ptr_arr_t[6];
+
+typedef int *ptr_multiarr_t[7][8][9][10];
+
+typedef int * (*fn_ptr_arr_t[11])();
+
+typedef int * (*fn_ptr_multiarr_t[12][13])();
+
+struct root_struct {
+	arr_t _1;
+	multiarr_t _2;
+	ptr_arr_t _3;
+	ptr_multiarr_t _4;
+	fn_ptr_arr_t _5;
+	fn_ptr_multiarr_t _6;
+};
+
+/* ------ END-EXPECTED-OUTPUT ------ */
+
+int f(struct root_struct *s)
+{
+	return 0;
+}

tools/testing/selftests/bpf/progs/btf_dump_test_case_namespacing.c

@@ -0,0 +1,73 @@
+// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
+
+/*
+ * BTF-to-C dumper test validating no name versioning happens between
+ * independent C namespaces (struct/union/enum vs typedef/enum values).
+ *
+ * Copyright (c) 2019 Facebook
+ */
+/* ----- START-EXPECTED-OUTPUT ----- */
+struct S {
+	int S;
+	int U;
+};
+
+typedef struct S S;
+
+union U {
+	int S;
+	int U;
+};
+
+typedef union U U;
+
+enum E {
+	V = 0,
+};
+
+typedef enum E E;
+
+struct A {};
+
+union B {};
+
+enum C {
+	A = 1,
+	B = 2,
+	C = 3,
+};
+
+struct X {};
+
+union Y {};
+
+enum Z;
+
+typedef int X;
+
+typedef int Y;
+
+typedef int Z;
+
+/*------ END-EXPECTED-OUTPUT ------ */
+
+int f(struct {
+	struct S _1;
+	S _2;
+	union U _3;
+	U _4;
+	enum E _5;
+	E _6;
+	struct A a;
+	union B b;
+	enum C c;
+	struct X x;
+	union Y y;
+	enum Z *z;
+	X xx;
+	Y yy;
+	Z zz;
+} *_)
+{
+	return 0;
+}

tools/testing/selftests/bpf/progs/btf_dump_test_case_ordering.c

@@ -0,0 +1,63 @@
+// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
+
+/*
+ * BTF-to-C dumper test for topological sorting of dependent structs.
+ *
+ * Copyright (c) 2019 Facebook
+ */
+/* ----- START-EXPECTED-OUTPUT ----- */
+struct s1 {};
+
+struct s3;
+
+struct s4;
+
+struct s2 {
+	struct s2 *s2;
+	struct s3 *s3;
+	struct s4 *s4;
+};
+
+struct s3 {
+	struct s1 s1;
+	struct s2 s2;
+};
+
+struct s4 {
+	struct s1 s1;
+	struct s3 s3;
+};
+
+struct list_head {
+	struct list_head *next;
+	struct list_head *prev;
+};
+
+struct hlist_node {
+	struct hlist_node *next;
+	struct hlist_node **pprev;
+};
+
+struct hlist_head {
+	struct hlist_node *first;
+};
+
+struct callback_head {
+	struct callback_head *next;
+	void (*func)(struct callback_head *);
+};
+
+struct root_struct {
+	struct s4 s4;
+	struct list_head l;
+	struct hlist_node n;
+	struct hlist_head h;
+	struct callback_head cb;
+};
+
+/*------ END-EXPECTED-OUTPUT ------ */
+
+int f(struct root_struct *root)
+{
+	return 0;
+}

tools/testing/selftests/bpf/progs/btf_dump_test_case_packing.c

@@ -0,0 +1,75 @@
+// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
+
+/*
+ * BTF-to-C dumper tests for struct packing determination.
+ *
+ * Copyright (c) 2019 Facebook
+ */
+/* ----- START-EXPECTED-OUTPUT ----- */
+struct packed_trailing_space {
+	int a;
+	short b;
+} __attribute__((packed));
+
+struct non_packed_trailing_space {
+	int a;
+	short b;
+};
+
+struct packed_fields {
+	short a;
+	int b;
+} __attribute__((packed));
+
+struct non_packed_fields {
+	short a;
+	int b;
+};
+
+struct nested_packed {
+	char: 4;
+	int a: 4;
+	long int b;
+	struct {
+		char c;
+		int d;
+	} __attribute__((packed)) e;
+} __attribute__((packed));
+
+union union_is_never_packed {
+	int a: 4;
+	char b;
+	char c: 1;
+};
+
+union union_does_not_need_packing {
+	struct {
+		long int a;
+		int b;
+	} __attribute__((packed));
+	int c;
+};
+
+union jump_code_union {
+	char code[5];
+	struct {
+		char jump;
+		int offset;
+	} __attribute__((packed));
+};
+
+/*------ END-EXPECTED-OUTPUT ------ */
+
+int f(struct {
+	struct packed_trailing_space _1;
+	struct non_packed_trailing_space _2;
+	struct packed_fields _3;
+	struct non_packed_fields _4;
+	struct nested_packed _5;
+	union union_is_never_packed _6;
+	union union_does_not_need_packing _7;
+	union jump_code_union _8;
+} *_)
+{
+	return 0;
+}

tools/testing/selftests/bpf/progs/btf_dump_test_case_padding.c

@@ -0,0 +1,111 @@
+// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
+
+/*
+ * BTF-to-C dumper tests for implicit and explicit padding between fields and
+ * at the end of a struct.
+ *
+ * Copyright (c) 2019 Facebook
+ */
+/* ----- START-EXPECTED-OUTPUT ----- */
+struct padded_implicitly {
+	int a;
+	long int b;
+	char c;
+};
+
+/* ------ END-EXPECTED-OUTPUT ------ */
+
+/* ----- START-EXPECTED-OUTPUT ----- */
+/*
+ *struct padded_explicitly {
+ *	int a;
+ *	int: 32;
+ *	int b;
+ *};
+ *
+ */
+/* ------ END-EXPECTED-OUTPUT ------ */
+
+struct padded_explicitly {
+	int a;
+	int: 1; /* algo will explicitly pad with full 32 bits here */
+	int b;
+};
+
+/* ----- START-EXPECTED-OUTPUT ----- */
+/*
+ *struct padded_a_lot {
+ *	int a;
+ *	long: 32;
+ *	long: 64;
+ *	long: 64;
+ *	int b;
+ *};
+ *
+ */
+/* ------ END-EXPECTED-OUTPUT ------ */
+
+struct padded_a_lot {
+	int a;
+	/* 32 bit of implicit padding here, which algo will make explicit */
+	long: 64;
+	long: 64;
+	int b;
+};
+
+/* ----- START-EXPECTED-OUTPUT ----- */
+/*
+ *struct padded_cache_line {
+ *	int a;
+ *	long: 32;
+ *	long: 64;
+ *	long: 64;
+ *	long: 64;
+ *	int b;
+ *};
+ *
+ */
+/* ------ END-EXPECTED-OUTPUT ------ */
+
+struct padded_cache_line {
+	int a;
+	int b __attribute__((aligned(32)));
+};
+
+/* ----- START-EXPECTED-OUTPUT ----- */
+/*
+ *struct zone_padding {
+ *	char x[0];
+ *};
+ *
+ *struct zone {
+ *	int a;
+ *	short b;
+ *	short: 16;
+ *	struct zone_padding __pad__;
+ *};
+ *
+ */
+/* ------ END-EXPECTED-OUTPUT ------ */
+
+struct zone_padding {
+	char x[0];
+} __attribute__((__aligned__(8)));
+
+struct zone {
+	int a;
+	short b;
+	short: 16;
+	struct zone_padding __pad__;
+};
+
+int f(struct {
+	struct padded_implicitly _1;
+	struct padded_explicitly _2;
+	struct padded_a_lot _3;
+	struct padded_cache_line _4;
+	struct zone _5;
+} *_)
+{
+	return 0;
+}

tools/testing/selftests/bpf/progs/btf_dump_test_case_syntax.c

@@ -0,0 +1,229 @@
+// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
+
+/*
+ * BTF-to-C dumper test for majority of C syntax quirks.
+ *
+ * Copyright (c) 2019 Facebook
+ */
+/* ----- START-EXPECTED-OUTPUT ----- */
+enum e1 {
+	A = 0,
+	B = 1,
+};
+
+enum e2 {
+	C = 100,
+	D = -100,
+	E = 0,
+};
+
+typedef enum e2 e2_t;
+
+typedef enum {
+	F = 0,
+	G = 1,
+	H = 2,
+} e3_t;
+
+typedef int int_t;
+
+typedef volatile const int * volatile const crazy_ptr_t;
+
+typedef int *****we_need_to_go_deeper_ptr_t;
+
+typedef volatile const we_need_to_go_deeper_ptr_t * restrict * volatile * const * restrict volatile * restrict const * volatile const * restrict volatile const how_about_this_ptr_t;
+
+typedef int *ptr_arr_t[10];
+
+typedef void (*fn_ptr1_t)(int);
+
+typedef void (*printf_fn_t)(const char *, ...);
+
+/* ------ END-EXPECTED-OUTPUT ------ */
+/*
+ * While previous function pointers are pretty trivial (C-syntax-level
+ * trivial), the following are deciphered here for future generations:
+ *
+ * - `fn_ptr2_t`: function, taking anonymous struct as a first arg and pointer
+ *   to a function, that takes int and returns int, as a second arg; returning
+ *   a pointer to a const pointer to a char. Equivalent to:
+ *	typedef struct { int a; } s_t;
+ *	typedef int (*fn_t)(int);
+ *	typedef char * const * (*fn_ptr2_t)(s_t, fn_t);
+ *
+ * - `fn_complext_t`: pointer to a function returning struct and accepting
+ *   union and struct. All structs and enum are anonymous and defined inline.
+ *
+ * - `signal_t: pointer to a function accepting a pointer to a function as an
+ *   argument and returning pointer to a function as a result. Sane equivalent:
+ *	typedef void (*signal_handler_t)(int);
+ *	typedef signal_handler_t (*signal_ptr_t)(int, signal_handler_t);
+ *
+ * - fn_ptr_arr1_t: array of pointers to a function accepting pointer to
+ *   a pointer to an int and returning pointer to a char. Easy.
+ *
+ * - fn_ptr_arr2_t: array of const pointers to a function taking no arguments
+ *   and returning a const pointer to a function, that takes pointer to a
+ *   `int -> char *` function and returns pointer to a char. Equivalent:
+ *   typedef char * (*fn_input_t)(int);
+ *   typedef char * (*fn_output_outer_t)(fn_input_t);
+ *   typedef const fn_output_outer_t (* fn_output_inner_t)();
+ *   typedef const fn_output_inner_t fn_ptr_arr2_t[5];
+ */
+/* ----- START-EXPECTED-OUTPUT ----- */
+typedef char * const * (*fn_ptr2_t)(struct {
+	int a;
+}, int (*)(int));
+
+typedef struct {
+	int a;
+	void (*b)(int, struct {
+		int c;
+	}, union {
+		char d;
+		int e[5];
+	});
+} (*fn_complex_t)(union {
+	void *f;
+	char g[16];
+}, struct {
+	int h;
+});
+
+typedef void (* (*signal_t)(int, void (*)(int)))(int);
+
+typedef char * (*fn_ptr_arr1_t[10])(int **);
+
+typedef char * (* const (* const fn_ptr_arr2_t[5])())(char * (*)(int));
+
+struct struct_w_typedefs {
+	int_t a;
+	crazy_ptr_t b;
+	we_need_to_go_deeper_ptr_t c;
+	how_about_this_ptr_t d;
+	ptr_arr_t e;
+	fn_ptr1_t f;
+	printf_fn_t g;
+	fn_ptr2_t h;
+	fn_complex_t i;
+	signal_t j;
+	fn_ptr_arr1_t k;
+	fn_ptr_arr2_t l;
+};
+
+typedef struct {
+	int x;
+	int y;
+	int z;
+} anon_struct_t;
+
+struct struct_fwd;
+
+typedef struct struct_fwd struct_fwd_t;
+
+typedef struct struct_fwd *struct_fwd_ptr_t;
+
+union union_fwd;
+
+typedef union union_fwd union_fwd_t;
+
+typedef union union_fwd *union_fwd_ptr_t;
+
+struct struct_empty {};
+
+struct struct_simple {
+	int a;
+	char b;
+	const int_t *p;
+	struct struct_empty s;
+	enum e2 e;
+	enum {
+		ANON_VAL1 = 1,
+		ANON_VAL2 = 2,
+	} f;
+	int arr1[13];
+	enum e2 arr2[5];
+};
+
+union union_empty {};
+
+union union_simple {
+	void *ptr;
+	int num;
+	int_t num2;
+	union union_empty u;
+};
+
+struct struct_in_struct {
+	struct struct_simple simple;
+	union union_simple also_simple;
+	struct {
+		int a;
+	} not_so_hard_as_well;
+	union {
+		int b;
+		int c;
+	} anon_union_is_good;
+	struct {
+		int d;
+		int e;
+	};
+	union {
+		int f;
+		int g;
+	};
+};
+
+struct struct_with_embedded_stuff {
+	int a;
+	struct {
+		int b;
+		struct {
+			struct struct_with_embedded_stuff *c;
+			const char *d;
+		} e;
+		union {
+			volatile long int f;
+			void * restrict g;
+		};
+	};
+	union {
+		const int_t *h;
+		void (*i)(char, int, void *);
+	} j;
+	enum {
+		K = 100,
+		L = 200,
+	} m;
+	char n[16];
+	struct {
+		char o;
+		int p;
+		void (*q)(int);
+	} r[5];
+	struct struct_in_struct s[10];
+	int t[11];
+};
+
+struct root_struct {
+	enum e1 _1;
+	enum e2 _2;
+	e2_t _2_1;
+	e3_t _2_2;
+	struct struct_w_typedefs _3;
+	anon_struct_t _7;
+	struct struct_fwd *_8;
+	struct_fwd_t *_9;
+	struct_fwd_ptr_t _10;
+	union union_fwd *_11;
+	union_fwd_t *_12;
+	union_fwd_ptr_t _13;
+	struct struct_with_embedded_stuff _14;
+};
+
+/* ------ END-EXPECTED-OUTPUT ------ */
+
+int f(struct root_struct *s)
+{
+	return 0;
+}