Merge branch 'resolve_btfids'

Jiri Olsa says:

====================
This patchset adds:
  - support to generate BTF ID lists that are resolved during
    kernel linking and usable within kernel code with following
    macros:

      BTF_ID_LIST(bpf_skb_output_btf_ids)
      BTF_ID(struct, sk_buff)

    and access it in kernel code via:
      extern u32 bpf_skb_output_btf_ids[];

  - resolve_btfids tool that scans elf object for .BTF_ids
    section and resolves its symbols with BTF ID values
  - resolving of bpf_ctx_convert struct and several other
    objects with BTF_ID_LIST

v7 changes:
  - added more acks [Andrii]
  - added some name-conflicting entries and fixed resolve_btfids
    to process them properly [Andrii]
  - changed bpf_get_task_stack_proto to use BTF_IDS_LIST/BTF_ID
    macros [Andrii]
  - fixed selftest build for resolve_btfids test
====================
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

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
 ************
 

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
@@ -1053,9 +1054,10 @@ export mod_sign_cmd
 
 HOST_LIBELF_LIBS = $(shell pkg-config libelf --libs 2>/dev/null || echo -lelf)
 
-ifdef CONFIG_STACK_VALIDATION
-  has_libelf := $(call try-run,\
+has_libelf = $(call try-run,\
                echo "int main() {}" | $(HOSTCC) -xc -o /dev/null $(HOST_LIBELF_LIBS) -,1,0)
+
+ifdef CONFIG_STACK_VALIDATION
   ifeq ($(has_libelf),1)
     objtool_target := tools/objtool FORCE
   else
@@ -1064,6 +1066,14 @@ 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 +1185,7 @@ 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 +1198,7 @@ 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 +1209,11 @@ 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
 # ---------------------------------------------------------------------------
 

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

include/linux/btf_ids.h

+/* 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

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);
@@ -4079,96 +4077,17 @@ 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,

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,

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,

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,

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

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)
 

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

tools/bpf/resolve_btfids/Build

+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)

tools/bpf/resolve_btfids/Makefile

+# 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

tools/bpf/resolve_btfids/main.c

+// 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;
+}

tools/include/linux/btf_ids.h

+/* 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

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 */

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
 

tools/testing/selftests/bpf/prog_tests/resolve_btfids.c

+// 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;
+}

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

+// 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;
+}