From: Sascha Hauer <s.hauer@pengutronix.de>
To: Andrey Smirnov <andrew.smirnov@gmail.com>
Cc: Barebox List <barebox@lists.infradead.org>
Subject: Re: [PATCH] ARM: aarch64: Avoid relocations in runtime-offset.S
Date: Tue, 29 Jan 2019 10:44:39 +0100 [thread overview]
Message-ID: <20190129094439.bighzaslxca4lcnp@pengutronix.de> (raw)
In-Reply-To: <CAHQ1cqG8RS7VXCV5yYe_bWJ_79W4L4mHXYue+Kpz1s=s0DQ7SQ@mail.gmail.com>
On Mon, Jan 28, 2019 at 11:12:29AM -0800, Andrey Smirnov wrote:
> > > _However_, older toolchains (tested on 5.5.0), will only issue a
> > > R_AARCH64_RELATIVE, so memory location will contain only zeroes:
> > >
> > > 00000000000000a0 <get_runtime_offset>:
> > > a0: 10000000 adr x0, a0 <get_runtime_offset>
> > > a4: 58000061 ldr x1, b0 <linkadr>
> > > a8: eb010000 subs x0, x0, x1
> > > ac: d65f03c0 ret
> > >
> > > 00000000000000b0 <linkadr>:
> > > ...
> > >
> > > This leads to an very early crash and complete boot failure in the
> > > latter case.
> >
> > I can reproduce this issue here. As you can imagine I do not really like
> > this "fix". I have no idea what the proper solution is (other than
> > deprecating gcc5), so I am fine removing the "a" flag as you suggested.
> > I think though that we should add a big comment above this function
>
> Sure, will add the comment in v2.
>
> > *why* this lacks the "a" flag and that we can add it back once gcc5
> > is retired.
> >
>
> AFAICT, we don't want a relocation there even if GCC5 is deprecated
> and it will always be conveniently initialized for us. To turn the
> tables a bit, why do we need that "a" there? What's its purpose?
The "a" is for "allocatable" meaning that space should be allocated in
the output binary. If you put get_runtime_offset into its own section
(outside .text) without the "a" flag then the linker linker bails out
moaning about overlapping sections. I think the .text segment is
inherently allocatable somehow, but then I wonder why the "a" flag makes
a difference at all. It may just be a bug in the early aarc64
toolchains, who knows...
Sascha
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next prev parent reply other threads:[~2019-01-29 9:44 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-24 3:15 Andrey Smirnov
2019-01-28 8:56 ` Sascha Hauer
2019-01-28 19:12 ` Andrey Smirnov
2019-01-29 9:44 ` Sascha Hauer [this message]
2019-01-30 1:18 ` Andrey Smirnov
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