Re: ARM hard-float linker path - consensus

[Denys Dmytriyenko <denis@denix.org>]

On Fri, Apr 13, 2012 at 11:11:02AM -0700, Khem Raj wrote:
> FYI this will impact us in coming time. If someone has questions
> please bring it up

While it's a slightly unexpected outcome (/lib/ld-linux-armhf.so.3) it's still 
good to see some agreement here.

Do we want to make the necessary toolchain changes right away, or wait for 
them to propagate from upstream?

-- 
Denys


> ---------- Forwarded message ----------
> From: Steve McIntyre <steve.mcintyre@linaro.org>
> Date: Fri, Apr 13, 2012 at 10:37 AM
> Subject: ARM hard-float linker path - consensus
> To: cross-distro@lists.linaro.org
> Cc: libc-ports@sourceware.org, gcc-patches@gcc.gnu.org
> 
> 
> Hi folks,
> 
> As promised, here's minutes from the call we had this
> afternoon. Spoiler: the result we've agreed is
> 
>  /lib/ld-linux-armhf.so.3
> 
> And here's a transcription of the minutes from
> 
>  https://wiki.linaro.org/OfficeofCTO/HardFloat/LinkerPathCallApr2012
> 
> ========================================
> 
> Meeting: 13th April 2012, 15:00 UTC
> 
> Agenda
> ------
> 
>  * Debian/Ubuntu have so far built using /lib/arm-linux-gnueabihf/ld-linux.so.3
>  * Some other distros (Fedora, OpenSUSE) are still using
> /lib/ld-linux.so.3 option which matches the older soft-float ABI
>  * Some people are proposing /libhf/ld-linux.so.3 or
> /libhfp/ld-linux.so.3 (multilib)
>  * Some people proposed /lib/ld-arm-linux-gnueabihf.so.3 (similar to
> x86_64, libs still in /lib, from Michael Hope)
>  * What should we do as a community?
> 
> Present
> -------
> 
> Name               Affiliations
> 
> Steve McIntyre     ARM, Debian, Linaro
> Wookey             ARM, Debian, Linaro
> Richard Earnshaw   ARM, gcc
> Jeff Law           Fedora, Red Hat, gcc, glibc
> Jon Masters        Fedora, Red Hat
> Andrew Haley       Fedora, Red Hat, gcc
> Andreas Jaeger     SUSE, openSUSE, glibc
> Carlos O'Donnell   Mentor, gcc
> Steve Langasek     Canonical, Ubuntu, Debian
> Dann Frazier       Canonical, Ubuntu, Debian
> Adam Conrad        Canonical, Ubuntu, Debian
> Matthias Klose     Canonical, Ubuntu, Debian
> Mike Frysinger     Gentoo
> Dennis Gilmore     Fedora, Red Hat
> 
> Discussion
> ----------
> 
> We started with a couple of questions up front to establish the
> grounds for discussion:
> 
>  * We believed that decision makers were present for all the important
>   parties, i.e. all the arm hard-float distros, plus toolchain
>   developers. This meant that a decision taken at the meeting could
>   be implemented without needing further arguments/negotiations.
> 
>  * All the people present understood the importance of cross-distro
>   binary compatibility, and they all wanted it. This led to agreement
>   that we needed to agree on a standard path for the runtime linker
>   for ARM hard-float Linux binaries.
> 
> Debian and Ubuntu had so far been using the "multi-arch" path of
> /lib/arm-linux-gnueabihf/ld-linux.so.3. Fedora and OpenSUSE were thus
> far using /lib/ld-linux.so.3, the same as the soft-float ABI. Others
> had proposed alternative paths such as /libhf/ld-linux.so.3 or
> /libhfp/ld-linux.so.3 (multilib) or
> /lib/ld-arm-linux-gnueabihf.so.3. Discussion showed that none of these
> were found to be universally acceptable.
> 
> Two parties were likely to be soon affected by an agreement here:
> 
> 1. Ubuntu 12.04 (releasing with armhf in ~2 weeks)
> 
> Adam/Steve L agreed that all efforts would be put in to switch the
> compilers in Ubuntu to a new path before release. Default things like
> gcc would be correct, but less common tools might still be targetting
> the old path /lib/arm-linux-gnueabihf/ld-linux.so. at release. They
> could be fixed in the longer term and would not stop progress here.
> 
> 2. Mentor (Codebench due for release in ~1 week)
> 
> Carlos mentioned this - Codebench has been using /lib/ld-linux.so.3
> for hard-float binaries for some time and it was too late to change
> that for this upcoming release. Next release due in October. Suggested
> and accepted that this should be mentioned in release notes: if people
> want to use Codebench on some systems (Debian/Ubuntu and derivatives),
> they'll need to tweak their system setup. He may be able to do the
> linker change and rebuild in a point release in a few weeks.
> 
> It was briefly suggested that the soft-float linker should be renamed
> away from /lib/ld-linux.so.3 as well at this time, but that idea was
> quickly shot down.
> 
> Proposal #1: /lib/ld-armhf.so.3       (not generally liked)
> 
> Proposal #2: /lib/ld-linux-armhf.so.3 (not favourite, but considered
>                                       an acceptable compromise by all)
> 
> No need to go any further.
> 
> Conclusion
> ----------
> 
> All the people in the meeting agreed: the new runtime linker path for
> ARM hard-float Linux binaries was to be
> 
> /lib/ld-linux-armhf.so.3
> 
> ACTION: People at the meeting to present this decision to their
>        companies / communities and get the appropriate changes made.
> 
> Further discussion
> ------------------
> 
> General unhappiness with the mess that led to this meeting. Future
> planning needs to be better between the various groups for the next
> time we have a new CPU/ABI/whatever.
> 
> ACTION: Jon Masters to talk to the Linux Foundation about setting up a
>        forum for such discussions.
> 
> In the meantime, strong consensus to use the
> cross-distro@lists.linaro.org mailing list for any more conversations
> now we have people in contact.
> 
> ACTION: Steve McIntyre to write up the minutes and circulate. Include
>        an updated linker path patch for gcc to match the decision
>        made here.
> 
> More discussion about triplets and naming, but nothing came of it in
> the end. Distro folks have already decided what they're using and have
> patched various software to build appropriately. Richard wants to move
> gcc's config.guess to use arm-linux-gnueabihf; no strong objections to
> that.
> 
> Linker path patch for gcc
> -------------------------
> 
> Adapted from earlier work by Dann Frazier <dann.frazier@canonical.com>
> and Michael Hope <michael.hope@linaro.org>
> 
> 2012-04-13 Steve McIntyre <steve.mcintyre@linaro.org>
> 
>       * config/arm/linux-eabi.h (GLIBC_DYNAMIC_LINKER_HARD_FLOAT): Define.
>       (GLIBC_DYNAMIC_LINKER): Redefine to use the hard float path.
> 
> diff --git a/gcc/config/arm/linux-eabi.h b/gcc/config/arm/linux-eabi.h
> index 80bd825..8c9d2e7 100644
> --- a/gcc/config/arm/linux-eabi.h
> +++ b/gcc/config/arm/linux-eabi.h
> @@ -62,7 +62,11 @@
>  /* Use ld-linux.so.3 so that it will be possible to run "classic"
>    GNU/Linux binaries on an EABI system.  */
>  #undef  GLIBC_DYNAMIC_LINKER
> -#define GLIBC_DYNAMIC_LINKER "/lib/ld-linux.so.3"
> +#define GLIBC_DYNAMIC_LINKER_SOFT_FLOAT "/lib/ld-linux.so.3"
> +#define GLIBC_DYNAMIC_LINKER_HARD_FLOAT "/lib/ld-linux-armhf.so.3"
> +#define GLIBC_DYNAMIC_LINKER \
> +   "%{mfloat-abi=hard:" GLIBC_DYNAMIC_LINKER_HARD_FLOAT "} \
> +    %{!mfloat-abi=hard:" GLIBC_DYNAMIC_LINKER_SOFT_FLOAT "}"
> 
>  /* At this point, bpabi.h will have clobbered LINK_SPEC.  We want to
>    use the GNU/Linux version, not the generic BPABI version.  */
> 
> 
> Post-meeting on IRC
> -------------------
> 
> Suggested that Richard should push the change into gcc trunk
> ASAP. Steve McIntyre agreed to work on that with Richard.
> 
> Also suggested that we want to get a patch into glibc too to change
> the installation path for ARM hard-float. Andrew agreed to push glibc
> upstream for that.
> 
> Cheers,
> --
> Steve McIntyre                                steve.mcintyre@linaro.org
> <http://www.linaro.org/> Linaro.org | Open source software for ARM SoCs
> 
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