linux-kernel - Re: odd endianness toolchains for crosstool

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Message-ID: <CAK8P3a1kRXQrmNg4eQw0-P+Fzz_AvFooLg3=nQNQKMRwvL9DWQ@mail.gmail.com>
Date:   Mon, 25 Apr 2022 18:15:07 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: odd endianness toolchains for crosstool

On Mon, Apr 25, 2022 at 5:53 PM Jason A. Donenfeld <Jason@...c4.com> wrote:
>
> Hi Arnd,
>
> On Mon, Apr 25, 2022 at 05:39:34PM +0200, Arnd Bergmann wrote:
> > I can probably do that before migrating to the new machine, but I can't
> > promise how quickly I find time to start.
>
> Oh awesome. Will keep my eye out for it.
>
> > > (And also, build ppc32 with --enable-secureplt --with-long-double-64.)
> >
> > Can you explain what those are about? Is this related to the ELFv1
> > vs ELFv2 difference or something else? Is this needed in both the
> > ppc32 and ppc64 compilers that each come with both targets?
>
> For 32-bit, it is required. From
> <https://wiki.musl-libc.org/supported-platforms.html>:
>
>     powerpc (needs gcc built with --enable-secureplt
>     --with-long-double-64, and -Wl,--secure-plt to link dynamic
>     binaries.)
>
> And from the INSTALL file it says:
>
>     * PowerPC
>         * Compiler toolchain must provide 64-bit long double, not IBM
>           double-double or IEEE quad
>         * For dynamic linking, compiler toolchain must be configured for
>           "secure PLT" variant
>
> For 64-bit, I'm not sure, but I know that at least -mabi=elfv2 is required,
> and I think --with-long-double-64 too, according to documentation:
>
>     * PowerPC64
>         * Both little and big endian variants are supported
>         * Compiler toolchain must provide 64-bit long double, not IBM
>           double-double or IEEE quad
>         * Compiler toolchain must use the new (ELFv2) ABI regardless of
>           whether it is for little or big endian

Ok, I see. For all I can tell, the toolchain I built already uses both
--with-long-double-64
and --enable-secureplt, as those seemt to be the default for Linux.

Regarding the the ELF ABI, I'm not sure how to check, but I think it
only does ELFv1, which is the default for big-endian glibc.

       Arnd