Revert "Revert "kbuild: remove libelf checks from top Makefile""

This reverts commit a2480b4d7e.

LibELF is now linkable from the Android Kernel build infra thanks to a
recent patch making hermetic the default for all builds.

Bug: 191637574
Fixes: a2480b4d7e ("Revert "kbuild: remove libelf checks from top Makefile"")
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Change-Id: I6eb8aced5766ea759780d27e82b34256971fdf50

Makefile

@@ -1121,41 +1121,6 @@ export INSTALL_DTBS_PATH ?= $(INSTALL_PATH)/dtbs/$(KERNELRELEASE)
 MODLIB	= $(INSTALL_MOD_PATH)/lib/modules/$(KERNELRELEASE)
 export MODLIB
 
-HOST_LIBELF_LIBS = $(shell pkg-config libelf --libs 2>/dev/null || echo -lelf)
-
-has_libelf = $(call try-run,\
-               echo "int main() {}" | $(HOSTCC) $(KBUILD_HOSTLDFLAGS) -xc -o /dev/null $(HOST_LIBELF_LIBS) -,1,0)
-
-ifdef CONFIG_STACK_VALIDATION
-  ifeq ($(has_libelf),1)
-    objtool_target := tools/objtool FORCE
-  else
-    SKIP_STACK_VALIDATION := 1
-    export SKIP_STACK_VALIDATION
-  endif
-endif
-
-PHONY += resolve_btfids_clean
-
-resolve_btfids_O = $(abspath $(objtree))/tools/bpf/resolve_btfids
-
-# tools/bpf/resolve_btfids directory might not exist
-# in output directory, skip its clean in that case
-resolve_btfids_clean:
-ifneq ($(wildcard $(resolve_btfids_O)),)
-	$(Q)$(MAKE) -sC $(srctree)/tools/bpf/resolve_btfids O=$(resolve_btfids_O) clean
-endif
-
-ifdef CONFIG_BPF
-ifdef CONFIG_DEBUG_INFO_BTF
-  ifeq ($(has_libelf),1)
-    resolve_btfids_target := tools/bpf/resolve_btfids FORCE
-  else
-    ERROR_RESOLVE_BTFIDS := 1
-  endif
-endif # CONFIG_DEBUG_INFO_BTF
-endif # CONFIG_BPF
-
 PHONY += prepare0
 
 export extmod_prefix = $(if $(KBUILD_EXTMOD),$(KBUILD_EXTMOD)/)
@@ -1305,7 +1270,7 @@ prepare0: archprepare
 	$(Q)$(MAKE) $(build)=.
 
 # All the preparing..
-prepare: prepare0 prepare-objtool prepare-resolve_btfids
+prepare: prepare0
 
 PHONY += remove-stale-files
 remove-stale-files:
@@ -1322,26 +1287,6 @@ uapi-asm-generic:
 	$(Q)$(MAKE) $(asm-generic)=arch/$(SRCARCH)/include/generated/uapi/asm \
 	generic=include/uapi/asm-generic
 
-PHONY += prepare-objtool prepare-resolve_btfids
-prepare-objtool: $(objtool_target)
-ifeq ($(SKIP_STACK_VALIDATION),1)
-ifdef CONFIG_FTRACE_MCOUNT_USE_OBJTOOL
-	@echo "error: Cannot generate __mcount_loc for CONFIG_DYNAMIC_FTRACE=y, please install libelf-dev, libelf-devel or elfutils-libelf-devel" >&2
-	@false
-endif
-ifdef CONFIG_UNWINDER_ORC
-	@echo "error: Cannot generate ORC metadata for CONFIG_UNWINDER_ORC=y, please install libelf-dev, libelf-devel or elfutils-libelf-devel" >&2
-	@false
-else
-	@echo "warning: Cannot use CONFIG_STACK_VALIDATION=y, please install libelf-dev, libelf-devel or elfutils-libelf-devel" >&2
-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
 # ---------------------------------------------------------------------------
 
@@ -1415,6 +1360,27 @@ install: sub_make_done :=
 # ---------------------------------------------------------------------------
 # Tools
 
+ifdef CONFIG_STACK_VALIDATION
+prepare: tools/objtool
+endif
+
+ifdef CONFIG_BPF
+ifdef CONFIG_DEBUG_INFO_BTF
+prepare: tools/bpf/resolve_btfids
+endif
+endif
+
+PHONY += resolve_btfids_clean
+
+resolve_btfids_O = $(abspath $(objtree))/tools/bpf/resolve_btfids
+
+# tools/bpf/resolve_btfids directory might not exist
+# in output directory, skip its clean in that case
+resolve_btfids_clean:
+ifneq ($(wildcard $(resolve_btfids_O)),)
+	$(Q)$(MAKE) -sC $(srctree)/tools/bpf/resolve_btfids O=$(resolve_btfids_O) clean
+endif
+
 # Clear a bunch of variables before executing the submake
 ifeq ($(quiet),silent_)
 tools_silent=s

scripts/Makefile.build

@@ -225,7 +225,6 @@ endif # CONFIG_FTRACE_MCOUNT_USE_RECORDMCOUNT
 
 ifdef CONFIG_STACK_VALIDATION
 ifndef CONFIG_LTO_CLANG
-ifneq ($(SKIP_STACK_VALIDATION),1)
 
 __objtool_obj := $(objtree)/tools/objtool/objtool
 
@@ -239,7 +238,6 @@ objtool_obj = $(if $(patsubst y%,, \
 	$(OBJECT_FILES_NON_STANDARD_$(basetarget).o)$(OBJECT_FILES_NON_STANDARD)n), \
 	$(__objtool_obj))
 
-endif # SKIP_STACK_VALIDATION
 endif # CONFIG_LTO_CLANG
 endif # CONFIG_STACK_VALIDATION