Re: [PATCH 3/3] objtool: move tools/objtool/ to scripts/objtool/

Josh Poimboeuf
2019-03-05T14:46:40Z

On Tue, Mar 05, 2019 at 02:48:16PM +0900, Masahiro Yamada wrote:
> Tools that are globally needed for building the kernel are supposed to
> be put in the scripts/ directory, but objtool is the exceptional one.
>
> People were confused by objtool's Makefile since most of tools run on
> the target whereas objtool runs on the host machine. Some time ago,
> Douglas Anderson suggested to move tools/objtool/ to scripts/tools/
> (https://patchwork.kernel.org/patch/9983535/#20996057), but we did
> not go as far as submitting a patch at that time.
>
> Recently, Robin Meijboom reported that the generated files for objtool
> were never cleaned up. (https://patchwork.kernel.org/patch/10813797/)
>
> So, I looked into this to fix the distortion. Move tools/objtool/ to
> scripts/objtool/, and rewrite Makefiles in the Kbuild-ish manner.
>
> I also cleaned up the top-level Makefile by moving the libelf check
> scripts/objtool/Makefile.
>
> I see some benefits in this.
>
> [1] generated files under scripts/ are cleaned up by 'make mrproper'
>
> Currently, the generated files under tools/objtool/ are not cleaned up
> since the build system under tools/ is a complete different world.
>
> If we want to clean them up, it should be done by 'make mrproper'
> instead of 'make clean' since objtool is needed for building external
> modules.
>
> This commit naturally solves the issue since Kbuild cleans under
> scripts/ by 'make mrproper'.

Yes, but this can be solved instead with a one-line patch.

> [2] build log looks nicer
>
> Currently, the build log under tools/objtool/ shows absolute paths, and
> displays 'DESCEND objtool' every time for incremental building.
>
> Switching over to the standard Kbuild scheme will improve the log.
>
> Before:
>
> DESCEND objtool
> HOSTCC /home/masahiro/workspace/linux/tools/objtool/fixdep.o
> HOSTLD /home/masahiro/workspace/linux/tools/objtool/fixdep-in.o
> LINK /home/masahiro/workspace/linux/tools/objtool/fixdep
> CC /home/masahiro/workspace/linux/tools/objtool/exec-cmd.o
> CC /home/masahiro/workspace/linux/tools/objtool/help.o
> CC /home/masahiro/workspace/linux/tools/objtool/pager.o
> CC /home/masahiro/workspace/linux/tools/objtool/parse-options.o
> CC /home/masahiro/workspace/linux/tools/objtool/run-command.o
> CC /home/masahiro/workspace/linux/tools/objtool/sigchain.o
> CC /home/masahiro/workspace/linux/tools/objtool/subcmd-config.o
> LD /home/masahiro/workspace/linux/tools/objtool/libsubcmd-in.o
> AR /home/masahiro/workspace/linux/tools/objtool/libsubcmd.a
> GEN /home/masahiro/workspace/linux/tools/objtool/arch/x86/lib/inat-tables.c
> CC /home/masahiro/workspace/linux/tools/objtool/arch/x86/decode.o
> LD /home/masahiro/workspace/linux/tools/objtool/arch/x86/objtool-in.o
> CC /home/masahiro/workspace/linux/tools/objtool/builtin-check.o
> CC /home/masahiro/workspace/linux/tools/objtool/builtin-orc.o
> CC /home/masahiro/workspace/linux/tools/objtool/check.o
> CC /home/masahiro/workspace/linux/tools/objtool/orc_gen.o
> CC /home/masahiro/workspace/linux/tools/objtool/orc_dump.o
> CC /home/masahiro/workspace/linux/tools/objtool/elf.o
> CC /home/masahiro/workspace/linux/tools/objtool/special.o
> CC /home/masahiro/workspace/linux/tools/objtool/objtool.o
> CC /home/masahiro/workspace/linux/tools/objtool/libstring.o
> CC /home/masahiro/workspace/linux/tools/objtool/str_error_r.o
> LD /home/masahiro/workspace/linux/tools/objtool/objtool-in.o
> LINK /home/masahiro/workspace/linux/tools/objtool/objtool
>
> After:
>
> HOSTCC scripts/objtool/builtin-check.o
> HOSTCC scripts/objtool/builtin-orc.o
> HOSTCC scripts/objtool/check.o
> HOSTCC scripts/objtool/orc_gen.o
> HOSTCC scripts/objtool/orc_dump.o
> HOSTCC scripts/objtool/elf.o
> HOSTCC scripts/objtool/special.o
> HOSTCC scripts/objtool/objtool.o
> HOSTCC scripts/objtool/libstring.o
> HOSTCC scripts/objtool/str_error_r.o
> HOSTCC scripts/objtool/exec-cmd.o
> HOSTCC scripts/objtool/pager.o
> HOSTCC scripts/objtool/parse-options.o
> HOSTCC scripts/objtool/run-command.o
> HOSTCC scripts/objtool/sigchain.o
> HOSTCC scripts/objtool/subcmd-config.o
> AWK scripts/objtool/arch/x86/lib/inat-tables.c
> HOSTCC scripts/objtool/arch/x86/decode.o
> HOSTLD scripts/objtool/objtool

That does look better.

> [3] simplify distro package script
>
> The special handling in scripts/package/buildeb is no longer needed
> since all host programs are copied to linux-headers packages.

I do see the benefits. In many ways objtool is a more natural fit in
the scripts dir. But there are also some downsides to this change:

- This will make it harder to package objtool as a standalone tool. It
has a lot of functionality that could be useful to other non-kernel
projects.

- It shares libsubcmd with perf. Including the subcmd .c files from
tools is hacky.

- It's disruptive: it will break all the out-of-tree distro kernel
packaging scripts which now look for objtool in tools.

You're right that objtool isn't a natural fit in tools, because it's
also used as part of the build. But it's not a natural fit in scripts
either. I think we've resolved most of those issues and it seems to be
working well these days.

So instead of disrupting everything because "make mrproper" doesn't
work, I think I'd rather just do the following:

diff --git a/Makefile b/Makefile
index ac5ac28a24e9..7e6696c9b862 100644
--- a/Makefile
+++ b/Makefile
@@ -1364,7 +1364,7 @@ PHONY += $(mrproper-dirs) mrproper
$(mrproper-dirs):
$(Q)$(MAKE) $(clean)=$(patsubst _mrproper_%,%,$@)

-mrproper: clean $(mrproper-dirs)
+mrproper: clean $(mrproper-dirs) tools/objtool_clean
$(call cmd,rmdirs)
$(call cmd,rmfiles)