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Date:   Mon, 08 Apr 2019 22:23:19 +0200
From:   Stefan Agner <stefan@agner.ch>
To:     Arnd Bergmann <arnd@arndb.de>
Cc:     Russell King - ARM Linux <linux@armlinux.org.uk>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Robin Murphy <robin.murphy@arm.com>,
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        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/3] ARM: use arch_extension directive instead of arch
 argument
In-Reply-To: <CAK8P3a0=-JBSkOO8=68QWvNagaHm7ij2aNOJ_1Oo9GyVSeTAoQ@mail.gmail.com>
References: <9641c58c03720104186a797a96e30a52ae9805e4.1553356359.git.stefan@agner.ch>
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On 31.03.2019 19:34, Arnd Bergmann wrote:
> On Sun, Mar 24, 2019 at 3:06 AM Arnd Bergmann <arnd@arndb.de> wrote:
>>
>> On Sat, Mar 23, 2019 at 4:52 PM Stefan Agner <stefan@agner.ch> wrote:
>> >
>> > The LLVM Target parser currently does not allow to specify the security
>> > extension as part of -march (see also LLVM Bug 40186 [0]). When trying
>> > to use Clang with LLVM's integrated assembler, this leads to a build
>> > errors such as this:
>> >   clang-8: error: the clang compiler does not support '-Wa,-march=armv7-a+sec'
>> >
>> > Use ".arch_extension sec" to enable the security extension in a more
>> > portable fasion.
>> >
>> > Note that this is technically not exactly the same as the old code
>> > checked for availabilty of the security extension by calling as-instr.
>> > However, there are already other sites which use ".arch_extension sec"
>> > unconditionally, hence de-facto we need an assembler capable of
>> > ".arch_extension sec" already today (arch/arm/mm/proc-v7.S). The
>> > arch extension "sec" is available since binutils 2.21 according to
>> > its documentation [1].
>> >
>> > [0] https://bugs.llvm.org/show_bug.cgi?id=40186
>> > [1] https://sourceware.org/binutils/docs-2.21/as/ARM-Options.html
>> >
>> > Signed-off-by: Stefan Agner <stefan@agner.ch>
>>
>> This sounds like a good idea. I think we have platform specific
>> minimum toolchain versions elsewhere, but I don't see a problem
>> with raising the minimum version for all the armv7ve platforms.
>>
>> I've added this patch to my randconfig test queue, but please
>> send it to arm@kernel.org for inclusion when you have
>> collected more Acks.
>>
>> Do you have a git tree with other patches required for the
>> integrated assembler? I might try that out as well with
>> my randconfig tree. At the moment I'm building with
>> clang-8 and a small number of patches on top.
>>
>> Acked-by: Arnd Bergmann <arnd@arndb.de>
> 
> I only now looked at the results and found a problem:
> In a mixed v6/v7 configuration, the arch_extension flag
> is not sufficient, and for armv6+sec, we get failures like
> 
> /git/arm-soc/arch/arm/mach-omap2/sleep44xx.S: Assembler messages:
> /git/arm-soc/arch/arm/mach-omap2/sleep44xx.S:343: Error: selected
> processor does not support `isb' in ARM mode
> /git/arm-soc/arch/arm/mach-omap2/sleep44xx.S:350: Error: selected
> processor does not support `dsb' in ARM mode
> /git/arm-soc/arch/arm/mach-omap2/sleep44xx.S:351: Error: selected
> processor does not support `dmb' in ARM mode
> clang: error: assembler command failed with exit code 1 (use -v to see
> invocation)
> /git/arm-soc/scripts/Makefile.build:369: recipe for target
> 'arch/arm/mach-omap2/sleep44xx.o' failed
> make[3]: *** [arch/arm/mach-omap2/sleep44xx.o] Error 1
> 
> ==> build/arm/0x64728DCE_defconfig/log <==
> /git/arm-soc/arch/arm/mach-omap2/omap-smc.S: Assembler messages:
> /git/arm-soc/arch/arm/mach-omap2/omap-smc.S:31: Error: selected
> processor does not support `dsb' in ARM mode
> /git/arm-soc/arch/arm/mach-omap2/omap-smc.S:53: Error: selected
> processor does not support `dsb' in ARM mode
> /git/arm-soc/arch/arm/mach-omap2/omap-smc.S:54: Error: selected
> processor does not support `dmb' in ARM mode


Hm, I guess I can just use .arch  armv7-a in those cases, as we use in
other places.

Thanks for testing! Will send a v2.

--
Stefan