From: Jiri Olsa <jolsa@kernel.org>
Date: Sat, 11 Jul 2020 23:53:22 +0200
Subject: bpf: Compile resolve_btfids tool at kernel compilation start
Patch-mainline: v5.9-rc1
Git-commit: 33a57ce0a54d498275f432db04850001175dfdfa
References: bsc#1177028

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
Acked-by: Gary Lin <glin@suse.com>
---
 Makefile           |   22 ++++++++++++++++++----
 tools/Makefile     |    3 +++
 tools/bpf/Makefile |    9 ++++++++-
 3 files changed, 29 insertions(+), 5 deletions(-)

--- a/Makefile
+++ b/Makefile
@@ -989,9 +989,10 @@ 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
@@ -1000,6 +1001,14 @@ 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 := $(if $(KBUILD_EXTMOD),$(KBUILD_EXTMOD)/)modules.order
@@ -1127,7 +1136,7 @@ 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
@@ -1140,7 +1149,7 @@ 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
@@ -1151,6 +1160,11 @@ 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
 # ---------------------------------------------------------------------------
 
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -66,6 +66,9 @@ cpupower: FORCE
 cgroup firewire hv guest 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)
 
--- a/tools/bpf/Makefile
+++ b/tools/bpf/Makefile
@@ -124,5 +124,12 @@ 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