From fbbb68de80a45ad66b66600bee275485c5073aa7 Mon Sep 17 00:00:00 2001
From: Jiri Olsa <jolsa@kernel.org>
Date: Sat, 11 Jul 2020 23:53:21 +0200
Subject: [PATCH 1/9] bpf: Add resolve_btfids tool to resolve BTF IDs in ELF
 object

The resolve_btfids tool scans elf object for .BTF_ids section
and resolves its symbols with BTF ID values.

It will be used to during linking time to resolve arrays of BTF
ID values used in verifier, so these IDs do not need to be
resolved in runtime.

The expected layout of .BTF_ids section is described in main.c
header. Related kernel changes are coming in following changes.

Build issue reported by 0-DAY CI Kernel Test Service.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200711215329.41165-2-jolsa@kernel.org
---
 tools/bpf/resolve_btfids/Build    |  10 +
 tools/bpf/resolve_btfids/Makefile |  77 ++++
 tools/bpf/resolve_btfids/main.c   | 721 ++++++++++++++++++++++++++++++
 3 files changed, 808 insertions(+)
 create mode 100644 tools/bpf/resolve_btfids/Build
 create mode 100644 tools/bpf/resolve_btfids/Makefile
 create mode 100644 tools/bpf/resolve_btfids/main.c

diff --git a/tools/bpf/resolve_btfids/Build b/tools/bpf/resolve_btfids/Build
new file mode 100644
index 0000000000000..ae82da03f9bf9
--- /dev/null
+++ b/tools/bpf/resolve_btfids/Build
@@ -0,0 +1,10 @@
+resolve_btfids-y += main.o
+resolve_btfids-y += rbtree.o
+resolve_btfids-y += zalloc.o
+resolve_btfids-y += string.o
+resolve_btfids-y += ctype.o
+resolve_btfids-y += str_error_r.o
+
+$(OUTPUT)%.o: ../../lib/%.c FORCE
+	$(call rule_mkdir)
+	$(call if_changed_dep,cc_o_c)
diff --git a/tools/bpf/resolve_btfids/Makefile b/tools/bpf/resolve_btfids/Makefile
new file mode 100644
index 0000000000000..948378ca73d4a
--- /dev/null
+++ b/tools/bpf/resolve_btfids/Makefile
@@ -0,0 +1,77 @@
+# SPDX-License-Identifier: GPL-2.0-only
+include ../../scripts/Makefile.include
+
+ifeq ($(srctree),)
+srctree := $(patsubst %/,%,$(dir $(CURDIR)))
+srctree := $(patsubst %/,%,$(dir $(srctree)))
+srctree := $(patsubst %/,%,$(dir $(srctree)))
+endif
+
+ifeq ($(V),1)
+  Q =
+  msg =
+else
+  Q = @
+  msg = @printf '  %-8s %s%s\n' "$(1)" "$(notdir $(2))" "$(if $(3), $(3))";
+  MAKEFLAGS=--no-print-directory
+endif
+
+OUTPUT ?= $(srctree)/tools/bpf/resolve_btfids/
+
+LIBBPF_SRC := $(srctree)/tools/lib/bpf/
+SUBCMD_SRC := $(srctree)/tools/lib/subcmd/
+
+BPFOBJ     := $(OUTPUT)/libbpf.a
+SUBCMDOBJ  := $(OUTPUT)/libsubcmd.a
+
+BINARY     := $(OUTPUT)/resolve_btfids
+BINARY_IN  := $(BINARY)-in.o
+
+all: $(BINARY)
+
+$(OUTPUT):
+	$(call msg,MKDIR,,$@)
+	$(Q)mkdir -p $(OUTPUT)
+
+$(SUBCMDOBJ): fixdep FORCE
+	$(Q)$(MAKE) -C $(SUBCMD_SRC) OUTPUT=$(OUTPUT)
+
+$(BPFOBJ): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile) | $(OUTPUT)
+	$(Q)$(MAKE) $(submake_extras) -C $(LIBBPF_SRC)  OUTPUT=$(abspath $(dir $@))/ $(abspath $@)
+
+CFLAGS := -g \
+          -I$(srctree)/tools/include \
+          -I$(srctree)/tools/include/uapi \
+          -I$(LIBBPF_SRC) \
+          -I$(SUBCMD_SRC)
+
+LIBS = -lelf -lz
+
+export srctree OUTPUT CFLAGS Q
+include $(srctree)/tools/build/Makefile.include
+
+$(BINARY_IN): fixdep FORCE
+	$(Q)$(MAKE) $(build)=resolve_btfids
+
+$(BINARY): $(BPFOBJ) $(SUBCMDOBJ) $(BINARY_IN)
+	$(call msg,LINK,$@)
+	$(Q)$(CC) $(BINARY_IN) $(LDFLAGS) -o $@ $(BPFOBJ) $(SUBCMDOBJ) $(LIBS)
+
+libsubcmd-clean:
+	$(Q)$(MAKE) -C $(SUBCMD_SRC) OUTPUT=$(OUTPUT) clean
+
+libbpf-clean:
+	$(Q)$(MAKE) -C $(LIBBPF_SRC) OUTPUT=$(OUTPUT) clean
+
+clean: libsubcmd-clean libbpf-clean fixdep-clean
+	$(call msg,CLEAN,$(BINARY))
+	$(Q)$(RM) -f $(BINARY); \
+	find $(if $(OUTPUT),$(OUTPUT),.) -name \*.o -or -name \*.o.cmd -or -name \*.o.d | xargs $(RM)
+
+tags:
+	$(call msg,GEN,,tags)
+	$(Q)ctags -R . $(LIBBPF_SRC) $(SUBCMD_SRC)
+
+FORCE:
+
+.PHONY: all FORCE clean tags
diff --git a/tools/bpf/resolve_btfids/main.c b/tools/bpf/resolve_btfids/main.c
new file mode 100644
index 0000000000000..6956b6350cade
--- /dev/null
+++ b/tools/bpf/resolve_btfids/main.c
@@ -0,0 +1,721 @@
+// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
+
+/*
+ * resolve_btfids scans Elf object for .BTF_ids section and resolves
+ * its symbols with BTF ID values.
+ *
+ * Each symbol points to 4 bytes data and is expected to have
+ * following name syntax:
+ *
+ * __BTF_ID__<type>__<symbol>[__<id>]
+ *
+ * type is:
+ *
+ *   func    - lookup BTF_KIND_FUNC symbol with <symbol> name
+ *             and store its ID into the data:
+ *
+ *             __BTF_ID__func__vfs_close__1:
+ *             .zero 4
+ *
+ *   struct  - lookup BTF_KIND_STRUCT symbol with <symbol> name
+ *             and store its ID into the data:
+ *
+ *             __BTF_ID__struct__sk_buff__1:
+ *             .zero 4
+ *
+ *   union   - lookup BTF_KIND_UNION symbol with <symbol> name
+ *             and store its ID into the data:
+ *
+ *             __BTF_ID__union__thread_union__1:
+ *             .zero 4
+ *
+ *   typedef - lookup BTF_KIND_TYPEDEF symbol with <symbol> name
+ *             and store its ID into the data:
+ *
+ *             __BTF_ID__typedef__pid_t__1:
+ *             .zero 4
+ *
+ *   set     - store symbol size into first 4 bytes and sort following
+ *             ID list
+ *
+ *             __BTF_ID__set__list:
+ *             .zero 4
+ *             list:
+ *             __BTF_ID__func__vfs_getattr__3:
+ *             .zero 4
+ *             __BTF_ID__func__vfs_fallocate__4:
+ *             .zero 4
+ */
+
+#define  _GNU_SOURCE
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <libelf.h>
+#include <gelf.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <errno.h>
+#include <linux/rbtree.h>
+#include <linux/zalloc.h>
+#include <linux/err.h>
+#include <btf.h>
+#include <libbpf.h>
+#include <parse-options.h>
+
+#define BTF_IDS_SECTION	".BTF_ids"
+#define BTF_ID		"__BTF_ID__"
+
+#define BTF_STRUCT	"struct"
+#define BTF_UNION	"union"
+#define BTF_TYPEDEF	"typedef"
+#define BTF_FUNC	"func"
+#define BTF_SET		"set"
+
+#define ADDR_CNT	100
+
+struct btf_id {
+	struct rb_node	 rb_node;
+	char		*name;
+	union {
+		int	 id;
+		int	 cnt;
+	};
+	int		 addr_cnt;
+	Elf64_Addr	 addr[ADDR_CNT];
+};
+
+struct object {
+	const char *path;
+	const char *btf;
+
+	struct {
+		int		 fd;
+		Elf		*elf;
+		Elf_Data	*symbols;
+		Elf_Data	*idlist;
+		int		 symbols_shndx;
+		int		 idlist_shndx;
+		size_t		 strtabidx;
+		unsigned long	 idlist_addr;
+	} efile;
+
+	struct rb_root	sets;
+	struct rb_root	structs;
+	struct rb_root	unions;
+	struct rb_root	typedefs;
+	struct rb_root	funcs;
+
+	int nr_funcs;
+	int nr_structs;
+	int nr_unions;
+	int nr_typedefs;
+};
+
+static int verbose;
+
+int eprintf(int level, int var, const char *fmt, ...)
+{
+	va_list args;
+	int ret;
+
+	if (var >= level) {
+		va_start(args, fmt);
+		ret = vfprintf(stderr, fmt, args);
+		va_end(args);
+	}
+	return ret;
+}
+
+#ifndef pr_fmt
+#define pr_fmt(fmt) fmt
+#endif
+
+#define pr_debug(fmt, ...) \
+	eprintf(1, verbose, pr_fmt(fmt), ##__VA_ARGS__)
+#define pr_debugN(n, fmt, ...) \
+	eprintf(n, verbose, pr_fmt(fmt), ##__VA_ARGS__)
+#define pr_debug2(fmt, ...) pr_debugN(2, pr_fmt(fmt), ##__VA_ARGS__)
+#define pr_err(fmt, ...) \
+	eprintf(0, verbose, pr_fmt(fmt), ##__VA_ARGS__)
+
+static bool is_btf_id(const char *name)
+{
+	return name && !strncmp(name, BTF_ID, sizeof(BTF_ID) - 1);
+}
+
+static struct btf_id *btf_id__find(struct rb_root *root, const char *name)
+{
+	struct rb_node *p = root->rb_node;
+	struct btf_id *id;
+	int cmp;
+
+	while (p) {
+		id = rb_entry(p, struct btf_id, rb_node);
+		cmp = strcmp(id->name, name);
+		if (cmp < 0)
+			p = p->rb_left;
+		else if (cmp > 0)
+			p = p->rb_right;
+		else
+			return id;
+	}
+	return NULL;
+}
+
+static struct btf_id*
+btf_id__add(struct rb_root *root, char *name, bool unique)
+{
+	struct rb_node **p = &root->rb_node;
+	struct rb_node *parent = NULL;
+	struct btf_id *id;
+	int cmp;
+
+	while (*p != NULL) {
+		parent = *p;
+		id = rb_entry(parent, struct btf_id, rb_node);
+		cmp = strcmp(id->name, name);
+		if (cmp < 0)
+			p = &(*p)->rb_left;
+		else if (cmp > 0)
+			p = &(*p)->rb_right;
+		else
+			return unique ? NULL : id;
+	}
+
+	id = zalloc(sizeof(*id));
+	if (id) {
+		pr_debug("adding symbol %s\n", name);
+		id->name = name;
+		rb_link_node(&id->rb_node, parent, p);
+		rb_insert_color(&id->rb_node, root);
+	}
+	return id;
+}
+
+static char *get_id(const char *prefix_end)
+{
+	/*
+	 * __BTF_ID__func__vfs_truncate__0
+	 * prefix_end =  ^
+	 */
+	char *p, *id = strdup(prefix_end + sizeof("__") - 1);
+
+	if (id) {
+		/*
+		 * __BTF_ID__func__vfs_truncate__0
+		 * id =            ^
+		 *
+		 * cut the unique id part
+		 */
+		p = strrchr(id, '_');
+		p--;
+		if (*p != '_') {
+			free(id);
+			return NULL;
+		}
+		*p = '\0';
+	}
+	return id;
+}
+
+static struct btf_id *add_symbol(struct rb_root *root, char *name, size_t size)
+{
+	char *id;
+
+	id = get_id(name + size);
+	if (!id) {
+		pr_err("FAILED to parse symbol name: %s\n", name);
+		return NULL;
+	}
+
+	return btf_id__add(root, id, false);
+}
+
+static int elf_collect(struct object *obj)
+{
+	Elf_Scn *scn = NULL;
+	size_t shdrstrndx;
+	int idx = 0;
+	Elf *elf;
+	int fd;
+
+	fd = open(obj->path, O_RDWR, 0666);
+	if (fd == -1) {
+		pr_err("FAILED cannot open %s: %s\n",
+			obj->path, strerror(errno));
+		return -1;
+	}
+
+	elf_version(EV_CURRENT);
+
+	elf = elf_begin(fd, ELF_C_RDWR_MMAP, NULL);
+	if (!elf) {
+		pr_err("FAILED cannot create ELF descriptor: %s\n",
+			elf_errmsg(-1));
+		return -1;
+	}
+
+	obj->efile.fd  = fd;
+	obj->efile.elf = elf;
+
+	elf_flagelf(elf, ELF_C_SET, ELF_F_LAYOUT);
+
+	if (elf_getshdrstrndx(elf, &shdrstrndx) != 0) {
+		pr_err("FAILED cannot get shdr str ndx\n");
+		return -1;
+	}
+
+	/*
+	 * Scan all the elf sections and look for save data
+	 * from .BTF_ids section and symbols.
+	 */
+	while ((scn = elf_nextscn(elf, scn)) != NULL) {
+		Elf_Data *data;
+		GElf_Shdr sh;
+		char *name;
+
+		idx++;
+		if (gelf_getshdr(scn, &sh) != &sh) {
+			pr_err("FAILED get section(%d) header\n", idx);
+			return -1;
+		}
+
+		name = elf_strptr(elf, shdrstrndx, sh.sh_name);
+		if (!name) {
+			pr_err("FAILED get section(%d) name\n", idx);
+			return -1;
+		}
+
+		data = elf_getdata(scn, 0);
+		if (!data) {
+			pr_err("FAILED to get section(%d) data from %s\n",
+				idx, name);
+			return -1;
+		}
+
+		pr_debug2("section(%d) %s, size %ld, link %d, flags %lx, type=%d\n",
+			  idx, name, (unsigned long) data->d_size,
+			  (int) sh.sh_link, (unsigned long) sh.sh_flags,
+			  (int) sh.sh_type);
+
+		if (sh.sh_type == SHT_SYMTAB) {
+			obj->efile.symbols       = data;
+			obj->efile.symbols_shndx = idx;
+			obj->efile.strtabidx     = sh.sh_link;
+		} else if (!strcmp(name, BTF_IDS_SECTION)) {
+			obj->efile.idlist       = data;
+			obj->efile.idlist_shndx = idx;
+			obj->efile.idlist_addr  = sh.sh_addr;
+		}
+	}
+
+	return 0;
+}
+
+static int symbols_collect(struct object *obj)
+{
+	Elf_Scn *scn = NULL;
+	int n, i, err = 0;
+	GElf_Shdr sh;
+	char *name;
+
+	scn = elf_getscn(obj->efile.elf, obj->efile.symbols_shndx);
+	if (!scn)
+		return -1;
+
+	if (gelf_getshdr(scn, &sh) != &sh)
+		return -1;
+
+	n = sh.sh_size / sh.sh_entsize;
+
+	/*
+	 * Scan symbols and look for the ones starting with
+	 * __BTF_ID__* over .BTF_ids section.
+	 */
+	for (i = 0; !err && i < n; i++) {
+		char *tmp, *prefix;
+		struct btf_id *id;
+		GElf_Sym sym;
+		int err = -1;
+
+		if (!gelf_getsym(obj->efile.symbols, i, &sym))
+			return -1;
+
+		if (sym.st_shndx != obj->efile.idlist_shndx)
+			continue;
+
+		name = elf_strptr(obj->efile.elf, obj->efile.strtabidx,
+				  sym.st_name);
+
+		if (!is_btf_id(name))
+			continue;
+
+		/*
+		 * __BTF_ID__TYPE__vfs_truncate__0
+		 * prefix =  ^
+		 */
+		prefix = name + sizeof(BTF_ID) - 1;
+
+		/* struct */
+		if (!strncmp(prefix, BTF_STRUCT, sizeof(BTF_STRUCT) - 1)) {
+			obj->nr_structs++;
+			id = add_symbol(&obj->structs, prefix, sizeof(BTF_STRUCT) - 1);
+		/* union  */
+		} else if (!strncmp(prefix, BTF_UNION, sizeof(BTF_UNION) - 1)) {
+			obj->nr_unions++;
+			id = add_symbol(&obj->unions, prefix, sizeof(BTF_UNION) - 1);
+		/* typedef */
+		} else if (!strncmp(prefix, BTF_TYPEDEF, sizeof(BTF_TYPEDEF) - 1)) {
+			obj->nr_typedefs++;
+			id = add_symbol(&obj->typedefs, prefix, sizeof(BTF_TYPEDEF) - 1);
+		/* func */
+		} else if (!strncmp(prefix, BTF_FUNC, sizeof(BTF_FUNC) - 1)) {
+			obj->nr_funcs++;
+			id = add_symbol(&obj->funcs, prefix, sizeof(BTF_FUNC) - 1);
+		/* set */
+		} else if (!strncmp(prefix, BTF_SET, sizeof(BTF_SET) - 1)) {
+			id = add_symbol(&obj->sets, prefix, sizeof(BTF_SET) - 1);
+			/*
+			 * SET objects store list's count, which is encoded
+			 * in symbol's size, together with 'cnt' field hence
+			 * that - 1.
+			 */
+			if (id)
+				id->cnt = sym.st_size / sizeof(int) - 1;
+		} else {
+			pr_err("FAILED unsupported prefix %s\n", prefix);
+			return -1;
+		}
+
+		if (!id)
+			return -ENOMEM;
+
+		if (id->addr_cnt >= ADDR_CNT) {
+			pr_err("FAILED symbol %s crossed the number of allowed lists",
+				id->name);
+			return -1;
+		}
+		id->addr[id->addr_cnt++] = sym.st_value;
+	}
+
+	return 0;
+}
+
+static struct btf *btf__parse_raw(const char *file)
+{
+	struct btf *btf;
+	struct stat st;
+	__u8 *buf;
+	FILE *f;
+
+	if (stat(file, &st))
+		return NULL;
+
+	f = fopen(file, "rb");
+	if (!f)
+		return NULL;
+
+	buf = malloc(st.st_size);
+	if (!buf) {
+		btf = ERR_PTR(-ENOMEM);
+		goto exit_close;
+	}
+
+	if ((size_t) st.st_size != fread(buf, 1, st.st_size, f)) {
+		btf = ERR_PTR(-EINVAL);
+		goto exit_free;
+	}
+
+	btf = btf__new(buf, st.st_size);
+
+exit_free:
+	free(buf);
+exit_close:
+	fclose(f);
+	return btf;
+}
+
+static bool is_btf_raw(const char *file)
+{
+	__u16 magic = 0;
+	int fd, nb_read;
+
+	fd = open(file, O_RDONLY);
+	if (fd < 0)
+		return false;
+
+	nb_read = read(fd, &magic, sizeof(magic));
+	close(fd);
+	return nb_read == sizeof(magic) && magic == BTF_MAGIC;
+}
+
+static struct btf *btf_open(const char *path)
+{
+	if (is_btf_raw(path))
+		return btf__parse_raw(path);
+	else
+		return btf__parse_elf(path, NULL);
+}
+
+static int symbols_resolve(struct object *obj)
+{
+	int nr_typedefs = obj->nr_typedefs;
+	int nr_structs  = obj->nr_structs;
+	int nr_unions   = obj->nr_unions;
+	int nr_funcs    = obj->nr_funcs;
+	int err, type_id;
+	struct btf *btf;
+	__u32 nr;
+
+	btf = btf_open(obj->btf ?: obj->path);
+	err = libbpf_get_error(btf);
+	if (err) {
+		pr_err("FAILED: load BTF from %s: %s",
+			obj->path, strerror(err));
+		return -1;
+	}
+
+	err = -1;
+	nr  = btf__get_nr_types(btf);
+
+	/*
+	 * Iterate all the BTF types and search for collected symbol IDs.
+	 */
+	for (type_id = 1; type_id <= nr; type_id++) {
+		const struct btf_type *type;
+		struct rb_root *root;
+		struct btf_id *id;
+		const char *str;
+		int *nr;
+
+		type = btf__type_by_id(btf, type_id);
+		if (!type) {
+			pr_err("FAILED: malformed BTF, can't resolve type for ID %d\n",
+				type_id);
+			goto out;
+		}
+
+		if (btf_is_func(type) && nr_funcs) {
+			nr   = &nr_funcs;
+			root = &obj->funcs;
+		} else if (btf_is_struct(type) && nr_structs) {
+			nr   = &nr_structs;
+			root = &obj->structs;
+		} else if (btf_is_union(type) && nr_unions) {
+			nr   = &nr_unions;
+			root = &obj->unions;
+		} else if (btf_is_typedef(type) && nr_typedefs) {
+			nr   = &nr_typedefs;
+			root = &obj->typedefs;
+		} else
+			continue;
+
+		str = btf__name_by_offset(btf, type->name_off);
+		if (!str) {
+			pr_err("FAILED: malformed BTF, can't resolve name for ID %d\n",
+				type_id);
+			goto out;
+		}
+
+		id = btf_id__find(root, str);
+		if (id) {
+			id->id = type_id;
+			(*nr)--;
+		}
+	}
+
+	err = 0;
+out:
+	btf__free(btf);
+	return err;
+}
+
+static int id_patch(struct object *obj, struct btf_id *id)
+{
+	Elf_Data *data = obj->efile.idlist;
+	int *ptr = data->d_buf;
+	int i;
+
+	if (!id->id) {
+		pr_err("FAILED unresolved symbol %s\n", id->name);
+		return -EINVAL;
+	}
+
+	for (i = 0; i < id->addr_cnt; i++) {
+		unsigned long addr = id->addr[i];
+		unsigned long idx = addr - obj->efile.idlist_addr;
+
+		pr_debug("patching addr %5lu: ID %7d [%s]\n",
+			 idx, id->id, id->name);
+
+		if (idx >= data->d_size) {
+			pr_err("FAILED patching index %lu out of bounds %lu\n",
+				idx, data->d_size);
+			return -1;
+		}
+
+		idx = idx / sizeof(int);
+		ptr[idx] = id->id;
+	}
+
+	return 0;
+}
+
+static int __symbols_patch(struct object *obj, struct rb_root *root)
+{
+	struct rb_node *next;
+	struct btf_id *id;
+
+	next = rb_first(root);
+	while (next) {
+		id = rb_entry(next, struct btf_id, rb_node);
+
+		if (id_patch(obj, id))
+			return -1;
+
+		next = rb_next(next);
+	}
+	return 0;
+}
+
+static int cmp_id(const void *pa, const void *pb)
+{
+	const int *a = pa, *b = pb;
+
+	return *a - *b;
+}
+
+static int sets_patch(struct object *obj)
+{
+	Elf_Data *data = obj->efile.idlist;
+	int *ptr = data->d_buf;
+	struct rb_node *next;
+
+	next = rb_first(&obj->sets);
+	while (next) {
+		unsigned long addr, idx;
+		struct btf_id *id;
+		int *base;
+		int cnt;
+
+		id   = rb_entry(next, struct btf_id, rb_node);
+		addr = id->addr[0];
+		idx  = addr - obj->efile.idlist_addr;
+
+		/* sets are unique */
+		if (id->addr_cnt != 1) {
+			pr_err("FAILED malformed data for set '%s'\n",
+				id->name);
+			return -1;
+		}
+
+		idx = idx / sizeof(int);
+		base = &ptr[idx] + 1;
+		cnt = ptr[idx];
+
+		pr_debug("sorting  addr %5lu: cnt %6d [%s]\n",
+			 (idx + 1) * sizeof(int), cnt, id->name);
+
+		qsort(base, cnt, sizeof(int), cmp_id);
+
+		next = rb_next(next);
+	}
+}
+
+static int symbols_patch(struct object *obj)
+{
+	int err;
+
+	if (__symbols_patch(obj, &obj->structs)  ||
+	    __symbols_patch(obj, &obj->unions)   ||
+	    __symbols_patch(obj, &obj->typedefs) ||
+	    __symbols_patch(obj, &obj->funcs)    ||
+	    __symbols_patch(obj, &obj->sets))
+		return -1;
+
+	if (sets_patch(obj))
+		return -1;
+
+	elf_flagdata(obj->efile.idlist, ELF_C_SET, ELF_F_DIRTY);
+
+	err = elf_update(obj->efile.elf, ELF_C_WRITE);
+	if (err < 0) {
+		pr_err("FAILED elf_update(WRITE): %s\n",
+			elf_errmsg(-1));
+	}
+
+	pr_debug("update %s for %s\n",
+		 err >= 0 ? "ok" : "failed", obj->path);
+	return err < 0 ? -1 : 0;
+}
+
+static const char * const resolve_btfids_usage[] = {
+	"resolve_btfids [<options>] <ELF object>",
+	NULL
+};
+
+int main(int argc, const char **argv)
+{
+	bool no_fail = false;
+	struct object obj = {
+		.efile = {
+			.idlist_shndx  = -1,
+			.symbols_shndx = -1,
+		},
+		.structs  = RB_ROOT,
+		.unions   = RB_ROOT,
+		.typedefs = RB_ROOT,
+		.funcs    = RB_ROOT,
+		.sets     = RB_ROOT,
+	};
+	struct option btfid_options[] = {
+		OPT_INCR('v', "verbose", &verbose,
+			 "be more verbose (show errors, etc)"),
+		OPT_STRING(0, "btf", &obj.btf, "BTF data",
+			   "BTF data"),
+		OPT_BOOLEAN(0, "no-fail", &no_fail,
+			   "do not fail if " BTF_IDS_SECTION " section is not found"),
+		OPT_END()
+	};
+	int err = -1;
+
+	argc = parse_options(argc, argv, btfid_options, resolve_btfids_usage,
+			     PARSE_OPT_STOP_AT_NON_OPTION);
+	if (argc != 1)
+		usage_with_options(resolve_btfids_usage, btfid_options);
+
+	obj.path = argv[0];
+
+	if (elf_collect(&obj))
+		goto out;
+
+	/*
+	 * We did not find .BTF_ids section or symbols section,
+	 * nothing to do..
+	 */
+	if (obj.efile.idlist_shndx == -1 ||
+	    obj.efile.symbols_shndx == -1) {
+		if (no_fail)
+			return 0;
+		pr_err("FAILED to find needed sections\n");
+		return -1;
+	}
+
+	if (symbols_collect(&obj))
+		goto out;
+
+	if (symbols_resolve(&obj))
+		goto out;
+
+	if (symbols_patch(&obj))
+		goto out;
+
+	err = 0;
+out:
+	if (obj.efile.elf)
+		elf_end(obj.efile.elf);
+	close(obj.efile.fd);
+	return err;
+}

From 33a57ce0a54d498275f432db04850001175dfdfa Mon Sep 17 00:00:00 2001
From: Jiri Olsa <jolsa@kernel.org>
Date: Sat, 11 Jul 2020 23:53:22 +0200
Subject: [PATCH 2/9] bpf: Compile resolve_btfids tool at kernel compilation
 start

The resolve_btfids tool will be used during the vmlinux linking,
so it's necessary it's ready for it.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Tested-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200711215329.41165-3-jolsa@kernel.org
---
 Makefile           | 22 ++++++++++++++++++----
 tools/Makefile     |  3 +++
 tools/bpf/Makefile |  9 ++++++++-
 3 files changed, 29 insertions(+), 5 deletions(-)

diff --git a/Makefile b/Makefile
index ac2c61c37a73e..017e775b32883 100644
--- a/Makefile
+++ b/Makefile
@@ -1053,9 +1053,10 @@ export mod_sign_cmd
 
 HOST_LIBELF_LIBS = $(shell pkg-config libelf --libs 2>/dev/null || echo -lelf)
 
+has_libelf = $(call try-run,\
+               echo "int main() {}" | $(HOSTCC) -xc -o /dev/null $(HOST_LIBELF_LIBS) -,1,0)
+
 ifdef CONFIG_STACK_VALIDATION
-  has_libelf := $(call try-run,\
-		echo "int main() {}" | $(HOSTCC) -xc -o /dev/null $(HOST_LIBELF_LIBS) -,1,0)
   ifeq ($(has_libelf),1)
     objtool_target := tools/objtool FORCE
   else
@@ -1064,6 +1065,14 @@ ifdef CONFIG_STACK_VALIDATION
   endif
 endif
 
+ifdef CONFIG_DEBUG_INFO_BTF
+  ifeq ($(has_libelf),1)
+    resolve_btfids_target := tools/bpf/resolve_btfids FORCE
+  else
+    ERROR_RESOLVE_BTFIDS := 1
+  endif
+endif
+
 PHONY += prepare0
 
 export MODORDER := $(extmod-prefix)modules.order
@@ -1175,7 +1184,7 @@ prepare0: archprepare
 	$(Q)$(MAKE) $(build)=.
 
 # All the preparing..
-prepare: prepare0 prepare-objtool
+prepare: prepare0 prepare-objtool prepare-resolve_btfids
 
 # Support for using generic headers in asm-generic
 asm-generic := -f $(srctree)/scripts/Makefile.asm-generic obj
@@ -1188,7 +1197,7 @@ uapi-asm-generic:
 	$(Q)$(MAKE) $(asm-generic)=arch/$(SRCARCH)/include/generated/uapi/asm \
 	generic=include/uapi/asm-generic
 
-PHONY += prepare-objtool
+PHONY += prepare-objtool prepare-resolve_btfids
 prepare-objtool: $(objtool_target)
 ifeq ($(SKIP_STACK_VALIDATION),1)
 ifdef CONFIG_UNWINDER_ORC
@@ -1199,6 +1208,11 @@ else
 endif
 endif
 
+prepare-resolve_btfids: $(resolve_btfids_target)
+ifeq ($(ERROR_RESOLVE_BTFIDS),1)
+	@echo "error: Cannot resolve BTF IDs for CONFIG_DEBUG_INFO_BTF, please install libelf-dev, libelf-devel or elfutils-libelf-devel" >&2
+	@false
+endif
 # Generate some files
 # ---------------------------------------------------------------------------
 
diff --git a/tools/Makefile b/tools/Makefile
index bd778812e9157..85af6ebbce912 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -67,6 +67,9 @@ cpupower: FORCE
 cgroup firewire hv guest bootconfig spi usb virtio vm bpf iio gpio objtool leds wmi pci firmware debugging: FORCE
 	$(call descend,$@)
 
+bpf/%: FORCE
+	$(call descend,$@)
+
 liblockdep: FORCE
 	$(call descend,lib/lockdep)
 
diff --git a/tools/bpf/Makefile b/tools/bpf/Makefile
index 6df1850f83530..74bc9a1052253 100644
--- a/tools/bpf/Makefile
+++ b/tools/bpf/Makefile
@@ -123,5 +123,12 @@ runqslower_install:
 runqslower_clean:
 	$(call descend,runqslower,clean)
 
+resolve_btfids:
+	$(call descend,resolve_btfids)
+
+resolve_btfids_clean:
+	$(call descend,resolve_btfids,clean)
+
 .PHONY: all install clean bpftool bpftool_install bpftool_clean \
-	runqslower runqslower_install runqslower_clean
+	runqslower runqslower_install runqslower_clean \
+	resolve_btfids resolve_btfids_clean

From 5a2798ab32ba2952cfe25701ee460bccbd434c75 Mon Sep 17 00:00:00 2001
From: Jiri Olsa <jolsa@kernel.org>
Date: Sat, 11 Jul 2020 23:53:23 +0200
Subject: [PATCH 3/9] bpf: Add BTF_ID_LIST/BTF_ID/BTF_ID_UNUSED macros

Adding support to generate .BTF_ids section that will hold BTF
ID lists for verifier.

Adding macros that will help to define lists of BTF ID values
placed in .BTF_ids section. They are initially filled with zeros
(during compilation) and resolved later during the linking phase
by resolve_btfids tool.

Following defines list of one BTF ID value:

  BTF_ID_LIST(bpf_skb_output_btf_ids)
  BTF_ID(struct, sk_buff)

It also defines following variable to access the list:

  extern u32 bpf_skb_output_btf_ids[];

The BTF_ID_UNUSED macro defines 4 zero bytes. It's used when we
want to define 'unused' entry in BTF_ID_LIST, like:

  BTF_ID_LIST(bpf_skb_output_btf_ids)
  BTF_ID(struct, sk_buff)
  BTF_ID_UNUSED
  BTF_ID(struct, task_struct)

Suggested-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Tested-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200711215329.41165-4-jolsa@kernel.org
---
 include/asm-generic/vmlinux.lds.h |  4 ++
 include/linux/btf_ids.h           | 87 +++++++++++++++++++++++++++++++
 2 files changed, 91 insertions(+)
 create mode 100644 include/linux/btf_ids.h

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index db600ef218d7d..0be2ee265931a 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -641,6 +641,10 @@
 		__start_BTF = .;					\
 		*(.BTF)							\
 		__stop_BTF = .;						\
+	}								\
+	. = ALIGN(4);							\
+	.BTF_ids : AT(ADDR(.BTF_ids) - LOAD_OFFSET) {			\
+		*(.BTF_ids)						\
 	}
 #else
 #define BTF
diff --git a/include/linux/btf_ids.h b/include/linux/btf_ids.h
new file mode 100644
index 0000000000000..fe019774f8a72
--- /dev/null
+++ b/include/linux/btf_ids.h
@@ -0,0 +1,87 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _LINUX_BTF_IDS_H
+#define _LINUX_BTF_IDS_H
+
+#include <linux/compiler.h> /* for __PASTE */
+
+/*
+ * Following macros help to define lists of BTF IDs placed
+ * in .BTF_ids section. They are initially filled with zeros
+ * (during compilation) and resolved later during the
+ * linking phase by resolve_btfids tool.
+ *
+ * Any change in list layout must be reflected in resolve_btfids
+ * tool logic.
+ */
+
+#define BTF_IDS_SECTION ".BTF_ids"
+
+#define ____BTF_ID(symbol)				\
+asm(							\
+".pushsection " BTF_IDS_SECTION ",\"a\";       \n"	\
+".local " #symbol " ;                          \n"	\
+".type  " #symbol ", @object;                  \n"	\
+".size  " #symbol ", 4;                        \n"	\
+#symbol ":                                     \n"	\
+".zero 4                                       \n"	\
+".popsection;                                  \n");
+
+#define __BTF_ID(symbol) \
+	____BTF_ID(symbol)
+
+#define __ID(prefix) \
+	__PASTE(prefix, __COUNTER__)
+
+/*
+ * The BTF_ID defines unique symbol for each ID pointing
+ * to 4 zero bytes.
+ */
+#define BTF_ID(prefix, name) \
+	__BTF_ID(__ID(__BTF_ID__##prefix##__##name##__))
+
+/*
+ * The BTF_ID_LIST macro defines pure (unsorted) list
+ * of BTF IDs, with following layout:
+ *
+ * BTF_ID_LIST(list1)
+ * BTF_ID(type1, name1)
+ * BTF_ID(type2, name2)
+ *
+ * list1:
+ * __BTF_ID__type1__name1__1:
+ * .zero 4
+ * __BTF_ID__type2__name2__2:
+ * .zero 4
+ *
+ */
+#define __BTF_ID_LIST(name)				\
+asm(							\
+".pushsection " BTF_IDS_SECTION ",\"a\";       \n"	\
+".local " #name ";                             \n"	\
+#name ":;                                      \n"	\
+".popsection;                                  \n");	\
+
+#define BTF_ID_LIST(name)				\
+__BTF_ID_LIST(name)					\
+extern u32 name[];
+
+/*
+ * The BTF_ID_UNUSED macro defines 4 zero bytes.
+ * It's used when we want to define 'unused' entry
+ * in BTF_ID_LIST, like:
+ *
+ *   BTF_ID_LIST(bpf_skb_output_btf_ids)
+ *   BTF_ID(struct, sk_buff)
+ *   BTF_ID_UNUSED
+ *   BTF_ID(struct, task_struct)
+ */
+
+#define BTF_ID_UNUSED					\
+asm(							\
+".pushsection " BTF_IDS_SECTION ",\"a\";       \n"	\
+".zero 4                                       \n"	\
+".popsection;                                  \n");
+
+
+#endif

From c9a0f3b85e09dd16665b639cb884490410619434 Mon Sep 17 00:00:00 2001
From: Jiri Olsa <jolsa@kernel.org>
Date: Sat, 11 Jul 2020 23:53:24 +0200
Subject: [PATCH 4/9] bpf: Resolve BTF IDs in vmlinux image

Using BTF_ID_LIST macro to define lists for several helpers
using BTF arguments.

And running resolve_btfids on vmlinux elf object during linking,
so the .BTF_ids section gets the IDs resolved.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Tested-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200711215329.41165-5-jolsa@kernel.org
---
 Makefile                 | 3 ++-
 kernel/bpf/stackmap.c    | 5 ++++-
 kernel/trace/bpf_trace.c | 9 +++++++--
 net/core/filter.c        | 9 +++++++--
 scripts/link-vmlinux.sh  | 6 ++++++
 5 files changed, 26 insertions(+), 6 deletions(-)

diff --git a/Makefile b/Makefile
index 017e775b32883..462f1a75fcb30 100644
--- a/Makefile
+++ b/Makefile
@@ -448,6 +448,7 @@ OBJSIZE		= $(CROSS_COMPILE)size
 STRIP		= $(CROSS_COMPILE)strip
 endif
 PAHOLE		= pahole
+RESOLVE_BTFIDS	= $(objtree)/tools/bpf/resolve_btfids/resolve_btfids
 LEX		= flex
 YACC		= bison
 AWK		= awk
@@ -510,7 +511,7 @@ GCC_PLUGINS_CFLAGS :=
 CLANG_FLAGS :=
 
 export ARCH SRCARCH CONFIG_SHELL BASH HOSTCC KBUILD_HOSTCFLAGS CROSS_COMPILE LD CC
-export CPP AR NM STRIP OBJCOPY OBJDUMP OBJSIZE READELF PAHOLE LEX YACC AWK INSTALLKERNEL
+export CPP AR NM STRIP OBJCOPY OBJDUMP OBJSIZE READELF PAHOLE RESOLVE_BTFIDS LEX YACC AWK INSTALLKERNEL
 export PERL PYTHON PYTHON3 CHECK CHECKFLAGS MAKE UTS_MACHINE HOSTCXX
 export KGZIP KBZIP2 KLZOP LZMA LZ4 XZ
 export KBUILD_HOSTCXXFLAGS KBUILD_HOSTLDFLAGS KBUILD_HOSTLDLIBS LDFLAGS_MODULE
diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
index a6c361ed7937b..48d8e739975fa 100644
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -9,6 +9,7 @@
 #include <linux/elf.h>
 #include <linux/pagemap.h>
 #include <linux/irq_work.h>
+#include <linux/btf_ids.h>
 #include "percpu_freelist.h"
 
 #define STACK_CREATE_FLAG_MASK					\
@@ -576,7 +577,9 @@ BPF_CALL_4(bpf_get_task_stack, struct task_struct *, task, void *, buf,
 	return __bpf_get_stack(regs, task, buf, size, flags);
 }
 
-static int bpf_get_task_stack_btf_ids[5];
+BTF_ID_LIST(bpf_get_task_stack_btf_ids)
+BTF_ID(struct, task_struct)
+
 const struct bpf_func_proto bpf_get_task_stack_proto = {
 	.func		= bpf_get_task_stack,
 	.gpl_only	= false,
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index e0b7775039ab9..e178e8e32b33e 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -13,6 +13,7 @@
 #include <linux/kprobes.h>
 #include <linux/syscalls.h>
 #include <linux/error-injection.h>
+#include <linux/btf_ids.h>
 
 #include <asm/tlb.h>
 
@@ -710,7 +711,9 @@ BPF_CALL_5(bpf_seq_printf, struct seq_file *, m, char *, fmt, u32, fmt_size,
 	return err;
 }
 
-static int bpf_seq_printf_btf_ids[5];
+BTF_ID_LIST(bpf_seq_printf_btf_ids)
+BTF_ID(struct, seq_file)
+
 static const struct bpf_func_proto bpf_seq_printf_proto = {
 	.func		= bpf_seq_printf,
 	.gpl_only	= true,
@@ -728,7 +731,9 @@ BPF_CALL_3(bpf_seq_write, struct seq_file *, m, const void *, data, u32, len)
 	return seq_write(m, data, len) ? -EOVERFLOW : 0;
 }
 
-static int bpf_seq_write_btf_ids[5];
+BTF_ID_LIST(bpf_seq_write_btf_ids)
+BTF_ID(struct, seq_file)
+
 static const struct bpf_func_proto bpf_seq_write_proto = {
 	.func		= bpf_seq_write,
 	.gpl_only	= true,
diff --git a/net/core/filter.c b/net/core/filter.c
index ddcc0d6209e1f..4e572441e64a6 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -75,6 +75,7 @@
 #include <net/ipv6_stubs.h>
 #include <net/bpf_sk_storage.h>
 #include <net/transp_v6.h>
+#include <linux/btf_ids.h>
 
 /**
  *	sk_filter_trim_cap - run a packet through a socket filter
@@ -3779,7 +3780,9 @@ static const struct bpf_func_proto bpf_skb_event_output_proto = {
 	.arg5_type	= ARG_CONST_SIZE_OR_ZERO,
 };
 
-static int bpf_skb_output_btf_ids[5];
+BTF_ID_LIST(bpf_skb_output_btf_ids)
+BTF_ID(struct, sk_buff)
+
 const struct bpf_func_proto bpf_skb_output_proto = {
 	.func		= bpf_skb_event_output,
 	.gpl_only	= true,
@@ -4173,7 +4176,9 @@ static const struct bpf_func_proto bpf_xdp_event_output_proto = {
 	.arg5_type	= ARG_CONST_SIZE_OR_ZERO,
 };
 
-static int bpf_xdp_output_btf_ids[5];
+BTF_ID_LIST(bpf_xdp_output_btf_ids)
+BTF_ID(struct, xdp_buff)
+
 const struct bpf_func_proto bpf_xdp_output_proto = {
 	.func		= bpf_xdp_event_output,
 	.gpl_only	= true,
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index 92dd745906f4a..e26f02dbedee4 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -336,6 +336,12 @@ fi
 
 vmlinux_link vmlinux "${kallsymso}" ${btf_vmlinux_bin_o}
 
+# fill in BTF IDs
+if [ -n "${CONFIG_DEBUG_INFO_BTF}" ]; then
+info BTFIDS vmlinux
+${RESOLVE_BTFIDS} vmlinux
+fi
+
 if [ -n "${CONFIG_BUILDTIME_TABLE_SORT}" ]; then
 	info SORTTAB vmlinux
 	if ! sorttable vmlinux; then

From 138b9a0511c789f2451ff1d80e7fd3f9eef3a9e3 Mon Sep 17 00:00:00 2001
From: Jiri Olsa <jolsa@kernel.org>
Date: Sat, 11 Jul 2020 23:53:25 +0200
Subject: [PATCH 5/9] bpf: Remove btf_id helpers resolving

Now when we moved the helpers btf_id arrays into .BTF_ids section,
we can remove the code that resolve those IDs in runtime.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Tested-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200711215329.41165-6-jolsa@kernel.org
---
 kernel/bpf/btf.c | 89 +++---------------------------------------------
 1 file changed, 5 insertions(+), 84 deletions(-)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 4c3007f428b16..71140b73ae3c4 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -4079,96 +4079,17 @@ int btf_struct_access(struct bpf_verifier_log *log,
 	return -EINVAL;
 }
 
-static int __btf_resolve_helper_id(struct bpf_verifier_log *log, void *fn,
-				   int arg)
-{
-	char fnname[KSYM_SYMBOL_LEN + 4] = "btf_";
-	const struct btf_param *args;
-	const struct btf_type *t;
-	const char *tname, *sym;
-	u32 btf_id, i;
-
-	if (IS_ERR(btf_vmlinux)) {
-		bpf_log(log, "btf_vmlinux is malformed\n");
-		return -EINVAL;
-	}
-
-	sym = kallsyms_lookup((long)fn, NULL, NULL, NULL, fnname + 4);
-	if (!sym) {
-		bpf_log(log, "kernel doesn't have kallsyms\n");
-		return -EFAULT;
-	}
-
-	for (i = 1; i <= btf_vmlinux->nr_types; i++) {
-		t = btf_type_by_id(btf_vmlinux, i);
-		if (BTF_INFO_KIND(t->info) != BTF_KIND_TYPEDEF)
-			continue;
-		tname = __btf_name_by_offset(btf_vmlinux, t->name_off);
-		if (!strcmp(tname, fnname))
-			break;
-	}
-	if (i > btf_vmlinux->nr_types) {
-		bpf_log(log, "helper %s type is not found\n", fnname);
-		return -ENOENT;
-	}
-
-	t = btf_type_by_id(btf_vmlinux, t->type);
-	if (!btf_type_is_ptr(t))
-		return -EFAULT;
-	t = btf_type_by_id(btf_vmlinux, t->type);
-	if (!btf_type_is_func_proto(t))
-		return -EFAULT;
-
-	args = (const struct btf_param *)(t + 1);
-	if (arg >= btf_type_vlen(t)) {
-		bpf_log(log, "bpf helper %s doesn't have %d-th argument\n",
-			fnname, arg);
-		return -EINVAL;
-	}
-
-	t = btf_type_by_id(btf_vmlinux, args[arg].type);
-	if (!btf_type_is_ptr(t) || !t->type) {
-		/* anything but the pointer to struct is a helper config bug */
-		bpf_log(log, "ARG_PTR_TO_BTF is misconfigured\n");
-		return -EFAULT;
-	}
-	btf_id = t->type;
-	t = btf_type_by_id(btf_vmlinux, t->type);
-	/* skip modifiers */
-	while (btf_type_is_modifier(t)) {
-		btf_id = t->type;
-		t = btf_type_by_id(btf_vmlinux, t->type);
-	}
-	if (!btf_type_is_struct(t)) {
-		bpf_log(log, "ARG_PTR_TO_BTF is not a struct\n");
-		return -EFAULT;
-	}
-	bpf_log(log, "helper %s arg%d has btf_id %d struct %s\n", fnname + 4,
-		arg, btf_id, __btf_name_by_offset(btf_vmlinux, t->name_off));
-	return btf_id;
-}
-
 int btf_resolve_helper_id(struct bpf_verifier_log *log,
 			  const struct bpf_func_proto *fn, int arg)
 {
-	int *btf_id = &fn->btf_id[arg];
-	int ret;
+	int id;
 
 	if (fn->arg_type[arg] != ARG_PTR_TO_BTF_ID)
 		return -EINVAL;
-
-	ret = READ_ONCE(*btf_id);
-	if (ret)
-		return ret;
-	/* ok to race the search. The result is the same */
-	ret = __btf_resolve_helper_id(log, fn->func, arg);
-	if (!ret) {
-		/* Function argument cannot be type 'void' */
-		bpf_log(log, "BTF resolution bug\n");
-		return -EFAULT;
-	}
-	WRITE_ONCE(*btf_id, ret);
-	return ret;
+	id = fn->btf_id[arg];
+	if (!id || id > btf_vmlinux->nr_types)
+		return -EINVAL;
+	return id;
 }
 
 static int __get_type_size(struct btf *btf, u32 btf_id,

From 49f4e6720748c778795df62d222d0200b61345be Mon Sep 17 00:00:00 2001
From: Jiri Olsa <jolsa@kernel.org>
Date: Sat, 11 Jul 2020 23:53:26 +0200
Subject: [PATCH 6/9] bpf: Use BTF_ID to resolve bpf_ctx_convert struct

This way the ID is resolved during compile time,
and we can remove the runtime name search.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Tested-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200711215329.41165-7-jolsa@kernel.org
---
 kernel/bpf/btf.c | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 71140b73ae3c4..a710e3ee1f180 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -18,6 +18,7 @@
 #include <linux/sort.h>
 #include <linux/bpf_verifier.h>
 #include <linux/btf.h>
+#include <linux/btf_ids.h>
 #include <linux/skmsg.h>
 #include <linux/perf_event.h>
 #include <net/sock.h>
@@ -3621,12 +3622,15 @@ static int btf_translate_to_vmlinux(struct bpf_verifier_log *log,
 	return kern_ctx_type->type;
 }
 
+BTF_ID_LIST(bpf_ctx_convert_btf_id)
+BTF_ID(struct, bpf_ctx_convert)
+
 struct btf *btf_parse_vmlinux(void)
 {
 	struct btf_verifier_env *env = NULL;
 	struct bpf_verifier_log *log;
 	struct btf *btf = NULL;
-	int err, btf_id;
+	int err;
 
 	env = kzalloc(sizeof(*env), GFP_KERNEL | __GFP_NOWARN);
 	if (!env)
@@ -3659,14 +3663,8 @@ struct btf *btf_parse_vmlinux(void)
 	if (err)
 		goto errout;
 
-	/* find struct bpf_ctx_convert for type checking later */
-	btf_id = btf_find_by_name_kind(btf, "bpf_ctx_convert", BTF_KIND_STRUCT);
-	if (btf_id < 0) {
-		err = btf_id;
-		goto errout;
-	}
 	/* btf_parse_vmlinux() runs under bpf_verifier_lock */
-	bpf_ctx_convert.t = btf_type_by_id(btf, btf_id);
+	bpf_ctx_convert.t = btf_type_by_id(btf, bpf_ctx_convert_btf_id[0]);
 
 	/* find bpf map structs for map_ptr access checking */
 	err = btf_vmlinux_map_ids_init(btf, log);

From 232ce4be295743deb2cf9a7cf9c60a4fde367964 Mon Sep 17 00:00:00 2001
From: Jiri Olsa <jolsa@kernel.org>
Date: Sat, 11 Jul 2020 23:53:27 +0200
Subject: [PATCH 7/9] bpf: Add info about .BTF_ids section to btf.rst

Updating btf.rst doc with info about .BTF_ids section

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Tested-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200711215329.41165-8-jolsa@kernel.org
---
 Documentation/bpf/btf.rst | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/Documentation/bpf/btf.rst b/Documentation/bpf/btf.rst
index 4d565d202ce36..b5361b8621c92 100644
--- a/Documentation/bpf/btf.rst
+++ b/Documentation/bpf/btf.rst
@@ -691,6 +691,42 @@ kernel API, the ``insn_off`` is the instruction offset in the unit of ``struct
 bpf_insn``. For ELF API, the ``insn_off`` is the byte offset from the
 beginning of section (``btf_ext_info_sec->sec_name_off``).
 
+4.2 .BTF_ids section
+====================
+
+The .BTF_ids section encodes BTF ID values that are used within the kernel.
+
+This section is created during the kernel compilation with the help of
+macros defined in ``include/linux/btf_ids.h`` header file. Kernel code can
+use them to create lists and sets (sorted lists) of BTF ID values.
+
+The ``BTF_ID_LIST`` and ``BTF_ID`` macros define unsorted list of BTF ID values,
+with following syntax::
+
+  BTF_ID_LIST(list)
+  BTF_ID(type1, name1)
+  BTF_ID(type2, name2)
+
+resulting in following layout in .BTF_ids section::
+
+  __BTF_ID__type1__name1__1:
+  .zero 4
+  __BTF_ID__type2__name2__2:
+  .zero 4
+
+The ``u32 list[];`` variable is defined to access the list.
+
+The ``BTF_ID_UNUSED`` macro defines 4 zero bytes. It's used when we
+want to define unused entry in BTF_ID_LIST, like::
+
+      BTF_ID_LIST(bpf_skb_output_btf_ids)
+      BTF_ID(struct, sk_buff)
+      BTF_ID_UNUSED
+      BTF_ID(struct, task_struct)
+
+All the BTF ID lists and sets are compiled in the .BTF_ids section and
+resolved during the linking phase of kernel build by ``resolve_btfids`` tool.
+
 5. Using BTF
 ************
 

From e5a0516ec9681daf5c1f0d05144d21430b6ca6d7 Mon Sep 17 00:00:00 2001
From: Jiri Olsa <jolsa@kernel.org>
Date: Sat, 11 Jul 2020 23:53:28 +0200
Subject: [PATCH 8/9] tools headers: Adopt verbatim copy of btf_ids.h from
 kernel sources

It will be needed by bpf selftest for resolve_btfids tool.

Also adding __PASTE macro as btf_ids.h dependency, which is
defined in:

  include/linux/compiler_types.h

but because tools/include do not have this header, I'm putting
the macro into linux/compiler.h header.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Tested-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200711215329.41165-9-jolsa@kernel.org
---
 tools/include/linux/btf_ids.h  | 87 ++++++++++++++++++++++++++++++++++
 tools/include/linux/compiler.h |  4 ++
 2 files changed, 91 insertions(+)
 create mode 100644 tools/include/linux/btf_ids.h

diff --git a/tools/include/linux/btf_ids.h b/tools/include/linux/btf_ids.h
new file mode 100644
index 0000000000000..fe019774f8a72
--- /dev/null
+++ b/tools/include/linux/btf_ids.h
@@ -0,0 +1,87 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _LINUX_BTF_IDS_H
+#define _LINUX_BTF_IDS_H
+
+#include <linux/compiler.h> /* for __PASTE */
+
+/*
+ * Following macros help to define lists of BTF IDs placed
+ * in .BTF_ids section. They are initially filled with zeros
+ * (during compilation) and resolved later during the
+ * linking phase by resolve_btfids tool.
+ *
+ * Any change in list layout must be reflected in resolve_btfids
+ * tool logic.
+ */
+
+#define BTF_IDS_SECTION ".BTF_ids"
+
+#define ____BTF_ID(symbol)				\
+asm(							\
+".pushsection " BTF_IDS_SECTION ",\"a\";       \n"	\
+".local " #symbol " ;                          \n"	\
+".type  " #symbol ", @object;                  \n"	\
+".size  " #symbol ", 4;                        \n"	\
+#symbol ":                                     \n"	\
+".zero 4                                       \n"	\
+".popsection;                                  \n");
+
+#define __BTF_ID(symbol) \
+	____BTF_ID(symbol)
+
+#define __ID(prefix) \
+	__PASTE(prefix, __COUNTER__)
+
+/*
+ * The BTF_ID defines unique symbol for each ID pointing
+ * to 4 zero bytes.
+ */
+#define BTF_ID(prefix, name) \
+	__BTF_ID(__ID(__BTF_ID__##prefix##__##name##__))
+
+/*
+ * The BTF_ID_LIST macro defines pure (unsorted) list
+ * of BTF IDs, with following layout:
+ *
+ * BTF_ID_LIST(list1)
+ * BTF_ID(type1, name1)
+ * BTF_ID(type2, name2)
+ *
+ * list1:
+ * __BTF_ID__type1__name1__1:
+ * .zero 4
+ * __BTF_ID__type2__name2__2:
+ * .zero 4
+ *
+ */
+#define __BTF_ID_LIST(name)				\
+asm(							\
+".pushsection " BTF_IDS_SECTION ",\"a\";       \n"	\
+".local " #name ";                             \n"	\
+#name ":;                                      \n"	\
+".popsection;                                  \n");	\
+
+#define BTF_ID_LIST(name)				\
+__BTF_ID_LIST(name)					\
+extern u32 name[];
+
+/*
+ * The BTF_ID_UNUSED macro defines 4 zero bytes.
+ * It's used when we want to define 'unused' entry
+ * in BTF_ID_LIST, like:
+ *
+ *   BTF_ID_LIST(bpf_skb_output_btf_ids)
+ *   BTF_ID(struct, sk_buff)
+ *   BTF_ID_UNUSED
+ *   BTF_ID(struct, task_struct)
+ */
+
+#define BTF_ID_UNUSED					\
+asm(							\
+".pushsection " BTF_IDS_SECTION ",\"a\";       \n"	\
+".zero 4                                       \n"	\
+".popsection;                                  \n");
+
+
+#endif
diff --git a/tools/include/linux/compiler.h b/tools/include/linux/compiler.h
index 9f9002734e192..6eac24d44e814 100644
--- a/tools/include/linux/compiler.h
+++ b/tools/include/linux/compiler.h
@@ -201,4 +201,8 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
 # define __fallthrough
 #endif
 
+/* Indirect macros required for expanded argument pasting, eg. __LINE__. */
+#define ___PASTE(a, b) a##b
+#define __PASTE(a, b) ___PASTE(a, b)
+
 #endif /* _TOOLS_LINUX_COMPILER_H */

From cc15a20d5f3abc3cbd7911b70156b7b9e2bc7d41 Mon Sep 17 00:00:00 2001
From: Jiri Olsa <jolsa@kernel.org>
Date: Sat, 11 Jul 2020 23:53:29 +0200
Subject: [PATCH 9/9] selftests/bpf: Add test for resolve_btfids

Adding resolve_btfids test under test_progs suite.

It's possible to use btf_ids.h header and its logic in
user space application, so we can add easy test for it.

The test defines BTF_ID_LIST and checks it gets properly
resolved.

For this reason the test_progs binary (and other binaries
that use TRUNNER* macros) is processed with resolve_btfids
tool, which resolves BTF IDs in .BTF_ids section. The BTF
data are taken from btf_data.o object rceated from
progs/btf_data.c.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Tested-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200711215329.41165-10-jolsa@kernel.org
---
 tools/testing/selftests/bpf/Makefile          |  15 ++-
 .../selftests/bpf/prog_tests/resolve_btfids.c | 111 ++++++++++++++++++
 tools/testing/selftests/bpf/progs/btf_data.c  |  50 ++++++++
 3 files changed, 175 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/resolve_btfids.c
 create mode 100644 tools/testing/selftests/bpf/progs/btf_data.c

diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index 1f9c696b3edf4..e7a8cf83ba48a 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -111,6 +111,7 @@ SCRATCH_DIR := $(OUTPUT)/tools
 BUILD_DIR := $(SCRATCH_DIR)/build
 INCLUDE_DIR := $(SCRATCH_DIR)/include
 BPFOBJ := $(BUILD_DIR)/libbpf/libbpf.a
+RESOLVE_BTFIDS := $(BUILD_DIR)/resolve_btfids/resolve_btfids
 
 # Define simple and short `make test_progs`, `make test_sysctl`, etc targets
 # to build individual tests.
@@ -177,7 +178,7 @@ $(BPFOBJ): $(wildcard $(BPFDIR)/*.[ch] $(BPFDIR)/Makefile)		       \
 	$(Q)$(MAKE) $(submake_extras) -C $(BPFDIR) OUTPUT=$(BUILD_DIR)/libbpf/ \
 		    DESTDIR=$(SCRATCH_DIR) prefix= all install_headers
 
-$(BUILD_DIR)/libbpf $(BUILD_DIR)/bpftool $(INCLUDE_DIR):
+$(BUILD_DIR)/libbpf $(BUILD_DIR)/bpftool $(BUILD_DIR)/resolve_btfids $(INCLUDE_DIR):
 	$(call msg,MKDIR,,$@)
 	mkdir -p $@
 
@@ -190,6 +191,16 @@ else
 	cp "$(VMLINUX_H)" $@
 endif
 
+$(RESOLVE_BTFIDS): $(BPFOBJ) | $(BUILD_DIR)/resolve_btfids	\
+		       $(TOOLSDIR)/bpf/resolve_btfids/main.c	\
+		       $(TOOLSDIR)/lib/rbtree.c			\
+		       $(TOOLSDIR)/lib/zalloc.c			\
+		       $(TOOLSDIR)/lib/string.c			\
+		       $(TOOLSDIR)/lib/ctype.c			\
+		       $(TOOLSDIR)/lib/str_error_r.c
+	$(Q)$(MAKE) $(submake_extras) -C $(TOOLSDIR)/bpf/resolve_btfids	\
+		OUTPUT=$(BUILD_DIR)/resolve_btfids/ BPFOBJ=$(BPFOBJ)
+
 # Get Clang's default includes on this system, as opposed to those seen by
 # '-target bpf'. This fixes "missing" files on some architectures/distros,
 # such as asm/byteorder.h, asm/socket.h, asm/sockios.h, sys/cdefs.h etc.
@@ -352,9 +363,11 @@ endif
 
 $(OUTPUT)/$(TRUNNER_BINARY): $(TRUNNER_TEST_OBJS)			\
 			     $(TRUNNER_EXTRA_OBJS) $$(BPFOBJ)		\
+			     $(RESOLVE_BTFIDS)				\
 			     | $(TRUNNER_BINARY)-extras
 	$$(call msg,BINARY,,$$@)
 	$$(CC) $$(CFLAGS) $$(filter %.a %.o,$$^) $$(LDLIBS) -o $$@
+	$(RESOLVE_BTFIDS) --no-fail --btf btf_data.o $$@
 
 endef
 
diff --git a/tools/testing/selftests/bpf/prog_tests/resolve_btfids.c b/tools/testing/selftests/bpf/prog_tests/resolve_btfids.c
new file mode 100644
index 0000000000000..403be6f36cba4
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/resolve_btfids.c
@@ -0,0 +1,111 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/err.h>
+#include <string.h>
+#include <bpf/btf.h>
+#include <bpf/libbpf.h>
+#include <linux/btf.h>
+#include <linux/kernel.h>
+#include <linux/btf_ids.h>
+#include "test_progs.h"
+
+static int duration;
+
+struct symbol {
+	const char	*name;
+	int		 type;
+	int		 id;
+};
+
+struct symbol test_symbols[] = {
+	{ "unused",  BTF_KIND_UNKN,     0 },
+	{ "S",       BTF_KIND_TYPEDEF, -1 },
+	{ "T",       BTF_KIND_TYPEDEF, -1 },
+	{ "U",       BTF_KIND_TYPEDEF, -1 },
+	{ "S",       BTF_KIND_STRUCT,  -1 },
+	{ "U",       BTF_KIND_UNION,   -1 },
+	{ "func",    BTF_KIND_FUNC,    -1 },
+};
+
+BTF_ID_LIST(test_list)
+BTF_ID_UNUSED
+BTF_ID(typedef, S)
+BTF_ID(typedef, T)
+BTF_ID(typedef, U)
+BTF_ID(struct,  S)
+BTF_ID(union,   U)
+BTF_ID(func,    func)
+
+static int
+__resolve_symbol(struct btf *btf, int type_id)
+{
+	const struct btf_type *type;
+	const char *str;
+	unsigned int i;
+
+	type = btf__type_by_id(btf, type_id);
+	if (!type) {
+		PRINT_FAIL("Failed to get type for ID %d\n", type_id);
+		return -1;
+	}
+
+	for (i = 0; i < ARRAY_SIZE(test_symbols); i++) {
+		if (test_symbols[i].id != -1)
+			continue;
+
+		if (BTF_INFO_KIND(type->info) != test_symbols[i].type)
+			continue;
+
+		str = btf__name_by_offset(btf, type->name_off);
+		if (!str) {
+			PRINT_FAIL("Failed to get name for BTF ID %d\n", type_id);
+			return -1;
+		}
+
+		if (!strcmp(str, test_symbols[i].name))
+			test_symbols[i].id = type_id;
+	}
+
+	return 0;
+}
+
+static int resolve_symbols(void)
+{
+	struct btf *btf;
+	int type_id;
+	__u32 nr;
+
+	btf = btf__parse_elf("btf_data.o", NULL);
+	if (CHECK(libbpf_get_error(btf), "resolve",
+		  "Failed to load BTF from btf_data.o\n"))
+		return -1;
+
+	nr = btf__get_nr_types(btf);
+
+	for (type_id = 1; type_id <= nr; type_id++) {
+		if (__resolve_symbol(btf, type_id))
+			break;
+	}
+
+	btf__free(btf);
+	return 0;
+}
+
+int test_resolve_btfids(void)
+{
+	unsigned int i;
+	int ret = 0;
+
+	if (resolve_symbols())
+		return -1;
+
+	/* Check BTF_ID_LIST(test_list) IDs */
+	for (i = 0; i < ARRAY_SIZE(test_symbols) && !ret; i++) {
+		ret = CHECK(test_list[i] != test_symbols[i].id,
+			    "id_check",
+			    "wrong ID for %s (%d != %d)\n", test_symbols[i].name,
+			    test_list[i], test_symbols[i].id);
+	}
+
+	return ret;
+}
diff --git a/tools/testing/selftests/bpf/progs/btf_data.c b/tools/testing/selftests/bpf/progs/btf_data.c
new file mode 100644
index 0000000000000..baa525275bde3
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/btf_data.c
@@ -0,0 +1,50 @@
+// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
+
+struct S {
+	int	a;
+	int	b;
+	int	c;
+};
+
+union U {
+	int	a;
+	int	b;
+	int	c;
+};
+
+struct S1 {
+	int	a;
+	int	b;
+	int	c;
+};
+
+union U1 {
+	int	a;
+	int	b;
+	int	c;
+};
+
+typedef int T;
+typedef int S;
+typedef int U;
+typedef int T1;
+typedef int S1;
+typedef int U1;
+
+struct root_struct {
+	S		m_1;
+	T		m_2;
+	U		m_3;
+	S1		m_4;
+	T1		m_5;
+	U1		m_6;
+	struct S	m_7;
+	struct S1	m_8;
+	union  U	m_9;
+	union  U1	m_10;
+};
+
+int func(struct root_struct *root)
+{
+	return 0;
+}