linux-kernel - Re: [PATCH v4 0/3] objtool build improvements

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Date:   Thu, 26 Jan 2023 11:34:26 -0800
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Nicolas Schier <nicolas@...sle.eu>,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        Stephane Eranian <eranian@...gle.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCH v4 0/3] objtool build improvements

On Thu, Jan 26, 2023 at 11:06:03AM -0800, Ian Rogers wrote:
> Install libsubcmd and then get headers from there, this avoids
> inadvertent dependencies on things in tools/lib. Fix V=1
> support. Clean up how HOSTCC is used to override CC to avoid CFLAGS
> being set for say gcc, and then CC being overridden to clang.
> 
> v4. Rebase and look to address review comments from Josh Poimboeuf
>     <jpoimboe@...nel.org>. Removes the reviewed-by/tested-by given
>     the scope of changes.
> v3. Is a rebase that removes the merged "tools lib subcmd: Add install
>     target" patch. In:
> https://lore.kernel.org/lkml/CAKwvOd=kgXmpfbVa1wiEvwL0tX3gu+dDTGi-HEiRXSojwCLRrg@mail.gmail.com/
>     Nick rightly points out that:
> WARNINGS := $(EXTRA_WARNINGS) -Wno-switch-default -Wno-switch-enum -Wno-packed -Wno-nested-externs
>     became:
> WARNINGS := -Wno-switch-default -Wno-switch-enum -Wno-packed -Wno-nested-externs
>     losing the EXTRA_WARNINGS which v3 now adds back in. Previous
>     testing had added the warnings to the end rather than the
>     beginning, thereby causing unexpected build issues that aren't present in v3.
> v2. Include required "tools lib subcmd: Add install target" that is
>     already in Arnaldo's tree:
> https://lore.kernel.org/lkml/20221109184914.1357295-3-irogers@google.com/
> https://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git/commit/?h=perf/core&id=630ae80ea1dd253609cb50cff87f3248f901aca3
>     When building libsubcmd.a from objtool's Makefile, clear the
>     subdir to avoid it being appended onto OUTPUT and breaking the
>     build.
> 
> Ian Rogers (3):
>   objtool: Install libsubcmd in build
>   objtool: Properly support make V=1
>   objtool: Alter how HOSTCC is forced

Thanks, this looks pretty good.  I might tweak the patch subjects to
describe what's being fixed from a user's perspective.

I'll wait a few days for any more reviews before merging.

Independently from this patch set, I discovered that HOSTCFLAGS (and
KBUILD_HOSTCFLAGS which includes -O2 and some other flags) don't work
when building objtool directly from tools/objtool.  But they do work
(for me at least) when building from the top-level Makefile.  So I'm not
sure what Nick's issue is.

-- 
Josh