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Date:   Fri, 27 May 2022 08:31:54 -0700
From:   Josh Poimboeuf <jpoimboe@kernel.org>
To:     Masahiro Yamada <masahiroy@kernel.org>
Cc:     linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org,
        Peter Zijlstra <peterz@infradead.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>, llvm@lists.linux.dev,
        Helge Deller <deller@gmx.de>, linux-parisc@vger.kernel.org,
        Nicolas Schier <nicolas@fjasle.eu>,
        Nathan Chancellor <nathan@kernel.org>,
        Sami Tolvanen <samitolvanen@google.com>,
        Sedat Dilek <sedat.dilek@gmail.com>,
        Michal Marek <michal.lkml@markovi.net>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Tom Rix <trix@redhat.com>
Subject: Re: [PATCH v7 2/8] kbuild: do not create *.prelink.o for Clang LTO
 or IBT
Message-ID: <20220527153154.hivyahzjz3txouoi@treble>
References: <20220527100155.1996314-1-masahiroy@kernel.org>
 <20220527100155.1996314-3-masahiroy@kernel.org>
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On Fri, May 27, 2022 at 07:01:49PM +0900, Masahiro Yamada wrote:
> New build flow
> ==============
> 
>  [1] single-object module
> 
>   Since there is only one object, there is no need to keep the LLVM IR.
>   Use $(CC)+$(LD) to generate an ELF object in one build rule. When LTO
>   is disabled, $(LD) is unneeded because $(CC) produces an ELF object.
> 
>                $(CC)+$(LD)+objtool              $(LD)
>     foo.c ----------------------------> foo.o ---------> foo.ko
>                                         (ELF)     |
>                                                   |
>                                       foo.mod.o --/
> 
>  [2] multi-object module
> 
>   Previously, $(AR) was used to combine LLVM bitcode into an archive,
>   but there was no technical reason to do so. Use $(LD) to merge them
>   into a single ELF object.
> 
>                                $(LD)
>              $(CC)            +objtool          $(LD)
>     foo1.c ---------> foo1.o ---------> foo.o ---------> foo.ko
>                                  |      (ELF)     |
>     foo2.c ---------> foo2.o ----/                |
>                      (LLVM IR)        foo.mod.o --/
> 
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
> Tested-by: Nathan Chancellor <nathan@kernel.org>
> Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
> Tested-by: Sedat Dilek <sedat.dilek@gmail.com> # LLVM-14 (x86-64)

Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>

-- 
Josh