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 btfid.c
header. Related kernel changes are coming in following changes.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
  tools/bpf/resolve_btfids/Build    |  26 ++
  tools/bpf/resolve_btfids/Makefile |  76 ++++
  tools/bpf/resolve_btfids/main.c   | 716 ++++++++++++++++++++++++++++++
  3 files changed, 818 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 000000000000..c7318cc55341
--- /dev/null
+++ b/tools/bpf/resolve_btfids/Build

@@ -0,0 +1,26 @@
+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)rbtree.o: ../../lib/rbtree.c FORCE
+	$(call rule_mkdir)
+	$(call if_changed_dep,cc_o_c)
+
+$(OUTPUT)zalloc.o: ../../lib/zalloc.c FORCE
+	$(call rule_mkdir)
+	$(call if_changed_dep,cc_o_c)
+
+$(OUTPUT)string.o: ../../lib/string.c FORCE
+	$(call rule_mkdir)
+	$(call if_changed_dep,cc_o_c)
+
+$(OUTPUT)ctype.o: ../../lib/ctype.c FORCE
+	$(call rule_mkdir)
+	$(call if_changed_dep,cc_o_c)
+
+$(OUTPUT)str_error_r.o: ../../lib/str_error_r.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 000000000000..f6502ff26573
--- /dev/null
+++ b/tools/bpf/resolve_btfids/Makefile

@@ -0,0 +1,76 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+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 000000000000..d758e2bdbc9d
--- /dev/null
+++ b/tools/bpf/resolve_btfids/main.c

@@ -0,0 +1,716 @@
+// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
+
+/*
+ * resolve_btfids scans Elf object for .BTF_ids section and resolves