LKML Archive on
help / color / mirror / Atom feed
From: "Martin Storsjö" <>
To: "Jason A. Donenfeld" <>
Subject: Re: [PATCH v2] arm: detect buggy binutils when in thumb2 mode
Date: Thu, 23 Nov 2017 14:01:44 +0200 (EET)	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Thu, 23 Nov 2017, Jason A. Donenfeld wrote:

> On older versions of binutils, \sym points to an aligned address. On
> newer versions of binutils, \sym sometimes points to the unaligned thumb
> address in certain circumstances. In order to homogenize this behavior,
> rather than adding 1, we could simply OR in 1, so that already unaligned
> instructions don't change. While that works, the downside is that we have
> to add an `orr` instruction to a fast path. The assembler can't do this at
> assemble time via "|1" because "invalid operands (.text and *ABS* sections)
> for `|'". A better solution would be to have consistent binutils behavior,
> but that ship has sailed.
> So, this commit adds a detection mechanism, which began as a small thing
> from Russell King that I then rewrote to use pure bash instead of
> shelling out, so that it doesn't slow down the build process. The detection
> mechanism _could_ be used to modify the assembly we generate, but for now
> it's just being used to catch buggy binutils and abort the build process in
> that case.
> The rest of this commit message contains all of the relevant information
> about the boot bug when compiled in thumb2 mode.
> My tests concerned these versions:
> broken: GNU ld (Gentoo 2.29.1 p3) 2.29.1
> working: GNU ld (GNU Binutils for Ubuntu) 2.26.1

FWIW, this issue stems from this change:

The same issue caused problems in libavcodec as well, where we chose to 
work around the issue in this fashion:;a=commitdiff;h=9dde6ab06c48f9447cd16f39bee33569cddb7be4;hp=547db1eaecd597031165a2bf637acaaacde52788

Related debian bug report, with a different workaround:

(In libav, we chose the workaround since the .eqv one suggested in the 
debian bug report didn't really work well with assemblers for other 

// Martin

  reply	other threads:[~2017-11-23 12:59 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <>
     [not found] ` <>
     [not found]   ` <>
     [not found]     ` <>
     [not found]       ` <>
     [not found]         ` <>
2017-11-23 10:47           ` Fwd: [PATCH] arm: ensure symbol is a thumb symbol in new binutils Jason A. Donenfeld
2017-11-23 11:48             ` [PATCH] arm: detect buggy binutils when in thumb2 mode Jason A. Donenfeld
2017-11-23 11:50               ` [PATCH v2] " Jason A. Donenfeld
2017-11-23 12:01                 ` Martin Storsjö [this message]
2017-11-23 14:02             ` Fwd: [PATCH] arm: ensure symbol is a thumb symbol in new binutils Russell King - ARM Linux
2017-11-23 14:26               ` Ard Biesheuvel

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \ \ \ \ \ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).