linux-kernel - Re: [PATCH v8 00/16] Add support for Clang LTO

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Message-ID: <20201206065028.GA2819096@ubuntu-m3-large-x86>
Date:   Sat, 5 Dec 2020 23:50:28 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Will Deacon <will@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        linux-arch <linux-arch@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kbuild <linux-kbuild@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        PCI <linux-pci@...r.kernel.org>, Jian Cai <jiancai@...gle.com>,
        Kristof Beyls <Kristof.Beyls@....com>
Subject: Re: [PATCH v8 00/16] Add support for Clang LTO

On Fri, Dec 04, 2020 at 02:52:41PM -0800, Sami Tolvanen wrote:
> On Thu, Dec 3, 2020 at 2:32 PM Nick Desaulniers <ndesaulniers@...gle.com> wrote:
> >
> > So I'd recommend to Sami to simply make the Kconfig also depend on
> > clang's integrated assembler (not just llvm-nm and llvm-ar).
> 
> Sure, sounds good to me. What's the preferred way to test for this in Kconfig?
> 
> It looks like actually trying to test if we have an LLVM assembler
> (e.g. using $(as-instr,.section
> ".linker-options","e",@llvm_linker_options)) doesn't work as Kconfig
> doesn't pass -no-integrated-as to clang here. I could do something
> simple like $(success,echo $(LLVM) $(LLVM_IAS) | grep -q "1 1").
> 
> Thoughts?
> 
> Sami

I think

    depends on $(success,test $(LLVM_IAS) -eq 1)

should work, at least according to my brief test.

Cheers,
Nathan