From: James Greenhalgh <james.greenhalgh@arm.com>
To: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
Cc: GCC Patches <gcc-patches@gcc.gnu.org>, nd <nd@arm.com>,
Richard Earnshaw <Richard.Earnshaw@arm.com>,
<marcus.shawcroft@arm.com>
Subject: Re: [PATCH v3][AArch64] Fix symbol offset limit
Date: Wed, 14 Jun 2017 14:07:00 -0000 [thread overview]
Message-ID: <20170614140702.GB8010@arm.com> (raw)
In-Reply-To: <VI1PR0802MB262180A56B715BD564EA12DA83C20@VI1PR0802MB2621.eurprd08.prod.outlook.com>
On Tue, Jun 13, 2017 at 03:00:28PM +0100, Wilco Dijkstra wrote:
>
> ping
I've been avoiding reviewing this patch as Richard was the last to comment
on it, and I wasn't sure that his comments had been resolved to his
satisfaction. The conversation was back in August 2016 on v1 of the patch:
> Richard Earnshaw (lists) <Richard.Earnshaw@arm.com> wrote:
> >
> > So isn't the real bug that we've permitted the user to create an object
> > that is too large for the data model?
>
> No that's a different issue I'm not trying to address here. The key is that as long
> as the start of the symbol is in range, we should be able to link. Due to optimization
> the offset may be huge even when the object is tiny, so the offset must be limited.
>
> > Consider, for example:
>
> char fixed_regs[0x200000000ULL];
> char fixed_regs2[100];
>
> int
> main()
> {
> return fixed_regs[0] + fixed_regs2[0];
> }
>
> > Neither offset is too large, but we still generate relocation errors
> > when trying to reference fixed_regs2.
>
> But so would creating a million objects of size 1. The linker could warn about
> large objects as well as giving better error messages for relocations that are
> out of range. But that's mostly QoI, what we have here is a case where legal
> code fails to link due to optimization. The original example is from GCC itself,
> the fixed_regs array is small but due to optimization we can end up with
> &fixed_regs + 0xffffffff.
Richard, do you have anything further to say on this patch? Or can we start
progressing the review again.
Thanks,
James
next prev parent reply other threads:[~2017-06-14 14:07 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-23 14:11 [PATCH][AArch64] " Wilco Dijkstra
2016-08-26 10:43 ` Richard Earnshaw (lists)
2016-08-26 19:07 ` Wilco Dijkstra
2016-09-12 15:30 ` [PATCH v2][AArch64] " Wilco Dijkstra
2016-09-21 14:48 ` Wilco Dijkstra
2016-10-17 12:42 ` Wilco Dijkstra
2016-10-25 9:47 ` Wilco Dijkstra
2016-11-02 16:48 ` Wilco Dijkstra
2016-11-14 13:07 ` Wilco Dijkstra
2016-12-06 15:07 ` Wilco Dijkstra
2017-01-17 15:14 ` [PATCH v3][AArch64] " Wilco Dijkstra
2017-02-02 14:44 ` Wilco Dijkstra
2017-02-23 16:58 ` Wilco Dijkstra
2017-04-20 16:03 ` Wilco Dijkstra
2017-06-13 14:00 ` Wilco Dijkstra
2017-06-14 14:07 ` James Greenhalgh [this message]
2017-06-14 16:03 ` Wilco Dijkstra
2017-06-15 15:13 ` Richard Earnshaw (lists)
2017-06-15 16:55 ` Wilco Dijkstra
2017-06-15 17:39 ` Richard Earnshaw (lists)
2017-06-15 17:51 ` Wilco Dijkstra
2017-06-15 18:11 ` Richard Earnshaw (lists)
2017-06-15 18:18 ` Wilco Dijkstra
2017-06-15 18:34 ` Richard Earnshaw (lists)
2017-06-15 18:55 ` Wilco Dijkstra
2017-06-15 19:52 ` Joseph Myers
2017-06-16 15:14 ` Nathan Sidwell
2017-06-27 15:36 ` Wilco Dijkstra
2017-07-14 14:28 ` Wilco Dijkstra
2017-07-21 11:23 ` Wilco Dijkstra
2017-08-01 10:19 ` Wilco Dijkstra
2017-08-15 17:36 ` Wilco Dijkstra
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