[PATCH 1/2] kbuild: hide tools/ build targets from external module builds

[PATCH 1/2] kbuild: hide tools/ build targets from external module builds

[Masahiro Yamada]

The tools/ directory only exists in the kernel source tree, not in
external modules.

Do not expose the meaningless targets to external modules.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
---

 Makefile | 30 ++++++++++++++++--------------
 1 file changed, 16 insertions(+), 14 deletions(-)

diff --git a/Makefile b/Makefile
index 7df040b1b023..d60dc028f09c 100644
--- a/Makefile
+++ b/Makefile
@@ -1351,6 +1351,22 @@ PHONY += scripts_unifdef
 scripts_unifdef: scripts_basic
 	$(Q)$(MAKE) $(build)=scripts scripts/unifdef
 
+# ---------------------------------------------------------------------------
+# Tools
+
+# Clear a bunch of variables before executing the submake
+ifeq ($(quiet),silent_)
+tools_silent=s
+endif
+
+tools/: FORCE
+	$(Q)mkdir -p $(objtree)/tools
+	$(Q)$(MAKE) LDFLAGS= MAKEFLAGS="$(tools_silent) $(filter --j% -j,$(MAKEFLAGS))" O=$(abspath $(objtree)) subdir=tools -C $(srctree)/tools/
+
+tools/%: FORCE
+	$(Q)mkdir -p $(objtree)/tools
+	$(Q)$(MAKE) LDFLAGS= MAKEFLAGS="$(tools_silent) $(filter --j% -j,$(MAKEFLAGS))" O=$(abspath $(objtree)) subdir=tools -C $(srctree)/tools/ $*
+
 # ---------------------------------------------------------------------------
 # Kernel selftest
 
@@ -1951,20 +1967,6 @@ kernelversion:
 image_name:
 	@echo $(KBUILD_IMAGE)
 
-# Clear a bunch of variables before executing the submake
-
-ifeq ($(quiet),silent_)
-tools_silent=s
-endif
-
-tools/: FORCE
-	$(Q)mkdir -p $(objtree)/tools
-	$(Q)$(MAKE) LDFLAGS= MAKEFLAGS="$(tools_silent) $(filter --j% -j,$(MAKEFLAGS))" O=$(abspath $(objtree)) subdir=tools -C $(srctree)/tools/
-
-tools/%: FORCE
-	$(Q)mkdir -p $(objtree)/tools
-	$(Q)$(MAKE) LDFLAGS= MAKEFLAGS="$(tools_silent) $(filter --j% -j,$(MAKEFLAGS))" O=$(abspath $(objtree)) subdir=tools -C $(srctree)/tools/ $*
-
 quiet_cmd_rmfiles = $(if $(wildcard $(rm-files)),CLEAN   $(wildcard $(rm-files)))
       cmd_rmfiles = rm -rf $(rm-files)
 
-- 
2.27.0

[PATCH 2/2] kbuild: remove libelf checks from top Makefile

[Masahiro Yamada]

I do not see a good reason why only the libelf development package must
be so carefully checked.

Kbuild generally does not check host tools or libraries.

For example, x86_64 defconfig fails to build with no libssl development
package installed.

scripts/extract-cert.c:21:10: fatal error: openssl/bio.h: No such file or directory
   21 | #include <openssl/bio.h>
      |          ^~~~~~~~~~~~~~~

To solve the build error, you need to install libssl-dev or openssl-devel
package, depending on your distribution.

'apt-file search', 'dnf provides', etc. is your frined to find a proper
package to install.

This commit removes all the libelf checks from the top Makefile.

If libelf is missing, objtool will fail to build in a similar pattern:

.../linux/tools/objtool/include/objtool/elf.h:10:10: fatal error: gelf.h: No such file or directory
   10 | #include <gelf.h>

You need to install libelf-dev, libelf-devel, or elfutils-libelf-devel
to proceed.

Another remarkable change is, CONFIG_STACK_VALIDATION (without
CONFIG_UNWINDER_ORC) previously continued to build with a warning,
but now it will treat missing libelf as an error.

This is just a one-time installation, so it should not matter to break
a build and make a user install the package.

BTW, the traditional way to handle such checks is autotool, but according
to [1], I do not expect the kernel build would have similar scripting
like './configure' does.

[1]: https://lore.kernel.org/lkml/CA+55aFzr2HTZVOuzpHYDwmtRJLsVzE-yqg2DHpHi_9ePsYp5ug@mail.gmail.com/

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
---

 Makefile                  | 78 +++++++++++----------------------------
 scripts/Makefile.build    |  2 -
 scripts/Makefile.modfinal |  2 -
 3 files changed, 22 insertions(+), 60 deletions(-)

diff --git a/Makefile b/Makefile
index d60dc028f09c..bfbb7c8cbb0f 100644
--- a/Makefile
+++ b/Makefile
@@ -1081,41 +1081,6 @@ 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)/)
@@ -1227,7 +1192,7 @@ prepare0: archprepare
 	$(Q)$(MAKE) $(build)=.
 
 # All the preparing..
-prepare: prepare0 prepare-objtool prepare-resolve_btfids
+prepare: prepare0
 
 PHONY += remove-stale-files
 remove-stale-files:
@@ -1244,26 +1209,6 @@ 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
 # ---------------------------------------------------------------------------
 
@@ -1354,6 +1299,27 @@ scripts_unifdef: scripts_basic
 # ---------------------------------------------------------------------------
 # 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
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 949f723efe53..7adc3a2c3c31 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -219,7 +219,6 @@ 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
 
@@ -233,7 +232,6 @@ 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
 
diff --git a/scripts/Makefile.modfinal b/scripts/Makefile.modfinal
index dd87cea9fba7..bdee3babc5cf 100644
--- a/scripts/Makefile.modfinal
+++ b/scripts/Makefile.modfinal
@@ -39,12 +39,10 @@ prelink-ext := .lto
 # so let's now process the prelinked binary before we link the module.
 
 ifdef CONFIG_STACK_VALIDATION
-ifneq ($(SKIP_STACK_VALIDATION),1)
 cmd_ld_ko_o +=								\
 	$(objtree)/tools/objtool/objtool $(objtool_args)		\
 		$(@:.ko=$(prelink-ext).o);
 
-endif # SKIP_STACK_VALIDATION
 endif # CONFIG_STACK_VALIDATION
 
 endif # CONFIG_LTO_CLANG
-- 
2.27.0

Re: [PATCH 2/2] kbuild: remove libelf checks from top Makefile

[Andrii Nakryiko]

On Tue, May 11, 2021 at 11:52 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> I do not see a good reason why only the libelf development package must
> be so carefully checked.
>
> Kbuild generally does not check host tools or libraries.
>
> For example, x86_64 defconfig fails to build with no libssl development
> package installed.
>
> scripts/extract-cert.c:21:10: fatal error: openssl/bio.h: No such file or directory
>    21 | #include <openssl/bio.h>
>       |          ^~~~~~~~~~~~~~~
>
> To solve the build error, you need to install libssl-dev or openssl-devel
> package, depending on your distribution.
>
> 'apt-file search', 'dnf provides', etc. is your frined to find a proper
> package to install.
>
> This commit removes all the libelf checks from the top Makefile.
>
> If libelf is missing, objtool will fail to build in a similar pattern:
>
> .../linux/tools/objtool/include/objtool/elf.h:10:10: fatal error: gelf.h: No such file or directory
>    10 | #include <gelf.h>
>
> You need to install libelf-dev, libelf-devel, or elfutils-libelf-devel
> to proceed.
>
> Another remarkable change is, CONFIG_STACK_VALIDATION (without
> CONFIG_UNWINDER_ORC) previously continued to build with a warning,
> but now it will treat missing libelf as an error.
>
> This is just a one-time installation, so it should not matter to break
> a build and make a user install the package.
>
> BTW, the traditional way to handle such checks is autotool, but according
> to [1], I do not expect the kernel build would have similar scripting
> like './configure' does.
>
> [1]: https://lore.kernel.org/lkml/CA+55aFzr2HTZVOuzpHYDwmtRJLsVzE-yqg2DHpHi_9ePsYp5ug@mail.gmail.com/
>
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> ---
>

resolve_btfids part looks good to me:

Acked-by: Andrii Nakryiko <andrii@kernel.org>

>  Makefile                  | 78 +++++++++++----------------------------
>  scripts/Makefile.build    |  2 -
>  scripts/Makefile.modfinal |  2 -
>  3 files changed, 22 insertions(+), 60 deletions(-)
>

[...]

Re: [PATCH 2/2] kbuild: remove libelf checks from top Makefile

[Masahiro Yamada]

(+CC: Josh, Peter)

On Thu, May 13, 2021 at 4:36 AM Andrii Nakryiko
<andrii.nakryiko@gmail.com> wrote:
>
> On Tue, May 11, 2021 at 11:52 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
> >
> > I do not see a good reason why only the libelf development package must
> > be so carefully checked.
> >
> > Kbuild generally does not check host tools or libraries.
> >
> > For example, x86_64 defconfig fails to build with no libssl development
> > package installed.
> >
> > scripts/extract-cert.c:21:10: fatal error: openssl/bio.h: No such file or directory
> >    21 | #include <openssl/bio.h>
> >       |          ^~~~~~~~~~~~~~~
> >
> > To solve the build error, you need to install libssl-dev or openssl-devel
> > package, depending on your distribution.
> >
> > 'apt-file search', 'dnf provides', etc. is your frined to find a proper
> > package to install.
> >
> > This commit removes all the libelf checks from the top Makefile.
> >
> > If libelf is missing, objtool will fail to build in a similar pattern:
> >
> > .../linux/tools/objtool/include/objtool/elf.h:10:10: fatal error: gelf.h: No such file or directory
> >    10 | #include <gelf.h>
> >
> > You need to install libelf-dev, libelf-devel, or elfutils-libelf-devel
> > to proceed.
> >
> > Another remarkable change is, CONFIG_STACK_VALIDATION (without
> > CONFIG_UNWINDER_ORC) previously continued to build with a warning,
> > but now it will treat missing libelf as an error.
> >
> > This is just a one-time installation, so it should not matter to break
> > a build and make a user install the package.
> >
> > BTW, the traditional way to handle such checks is autotool, but according
> > to [1], I do not expect the kernel build would have similar scripting
> > like './configure' does.
> >
> > [1]: https://lore.kernel.org/lkml/CA+55aFzr2HTZVOuzpHYDwmtRJLsVzE-yqg2DHpHi_9ePsYp5ug@mail.gmail.com/
> >
> > Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> > ---
> >
>
> resolve_btfids part looks good to me:
>
> Acked-by: Andrii Nakryiko <andrii@kernel.org>
>
> >  Makefile                  | 78 +++++++++++----------------------------
> >  scripts/Makefile.build    |  2 -
> >  scripts/Makefile.modfinal |  2 -
> >  3 files changed, 22 insertions(+), 60 deletions(-)
> >
>
> [...]



-- 
Best Regards
Masahiro Yamada