linux-kernel - Re: [PATCH v7 2/8] kbuild: do not create *.prelink.o for Clang LTO or IBT

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Message-ID: <20220527153154.hivyahzjz3txouoi@treble>
Date:   Fri, 27 May 2022 08:31:54 -0700
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>, llvm@...ts.linux.dev,
        Helge Deller <deller@....de>, linux-parisc@...r.kernel.org,
        Nicolas Schier <nicolas@...sle.eu>,
        Nathan Chancellor <nathan@...nel.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>
Subject: Re: [PATCH v7 2/8] kbuild: do not create *.prelink.o for Clang LTO
 or IBT

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@...nel.org>
> Reviewed-by: Nicolas Schier <nicolas@...sle.eu>
> Tested-by: Nathan Chancellor <nathan@...nel.org>
> Reviewed-by: Sami Tolvanen <samitolvanen@...gle.com>
> Tested-by: Sedat Dilek <sedat.dilek@...il.com> # LLVM-14 (x86-64)

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

-- 
Josh