linux-kernel - Re: odd endianness toolchains for crosstool

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Message-ID: <YmbD/oPIUBvJ/YjQ@zx2c4.com>
Date:   Mon, 25 Apr 2022 17:53:34 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: odd endianness toolchains for crosstool

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

Taken from <https://git.musl-libc.org/cgit/musl/tree/INSTALL#n35>.

Jason