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Date: Wed, 31 Oct 2018 18:50:32 +0100
From: Michal =?UTF-8?B?U3VjaMOhbmVr?= <msuchanek@suse.de>
Subject: Re: PIE binaries are no longer mapped below 4 GiB on ppc64le
Message-ID: <20181031185032.679e170a@naga.suse.cz>
In-Reply-To: <87k1lyf2x3.fsf@oldenburg.str.redhat.com>
References: <87k1lyf2x3.fsf@oldenburg.str.redhat.com>
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Sender: owner-linux-mm@kvack.org
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To: Florian Weimer <fweimer@redhat.com>
Cc: linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org

On Wed, 31 Oct 2018 18:20:56 +0100
Florian Weimer <fweimer@redhat.com> wrote:

> We tried to use Go to build PIE binaries, and while the Go toolchain
> is definitely not ready (it produces text relocations and problematic
> relocations in general), it exposed what could be an accidental
> userspace ABI change.
>=20
> With our 4.10-derived kernel, PIE binaries are mapped below 4 GiB, so
> relocations like R_PPC64_ADDR16_HA work:
>=20
...

> There are fewer mappings because the loader detects a relocation
> overflow and aborts (=E2=80=9Cerror while loading shared libraries:
> R_PPC64_ADDR16_HA reloc at 0x0000000120f0983c for symbol `' out of
> range=E2=80=9D), so I had to recover the mappings externally.  Disabling =
ASLR
> does not help.
>=20
...
>=20
> And it needs to be built with:
>=20
>   go build -ldflags=3D-extldflags=3D-pie extld.go
>=20
> I'm not entirely sure what to make of this, but I'm worried that this
> could be a regression that matters to userspace.

I encountered the same when trying to build go on ppc64le. I am not
familiar with the internals so I just let it be.

It does not seem to matter to any other userspace. Maybe it would be
good idea to generate 64bit relocations on 64bit targets?

Thanks

Michal