linux-arm-kernel.lists.infradead.org archive mirror
 help / color / mirror / Atom feed
From: dave.martin@linaro.org (Dave Martin)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] ARM: mxc: Correct data alignment in headsmp.S for CONFIG_THUMB2_KERNEL
Date: Tue, 16 Nov 2010 13:13:37 +0000	[thread overview]
Message-ID: <1289913217-8672-1-git-send-email-dave.martin@linaro.org> (raw)

Directives such as .long and .word do not magically cause the
assembler location counter to become aligned in gas.  As a
result, using these directives in code sections can result in
misaligned data words when building a Thumb-2 kernel
(CONFIG_THUMB2_KERNEL).

This is a Bad Thing, since the ABI permits the compiler to
assume that fundamental types of word size or above are word-
aligned when accessing them from C.  If the data is not really
word-aligned, this can cause impaired performance and stray
alignment faults in some circumstances.

In general, the following rules should be applied when using
data word declaration directives inside code sections:

    * .quad and .double:
         .align 3

    * .long, .word, .single, .float:
         .align (or .align 2)

    * .short:
        No explicit alignment required, since Thumb-2
        instructions are always 2 or 4 bytes in size.
        immediately after an instruction.

Applies cleanly on v2.6.37-rc1.

Signed-off-by: Dave Martin <dave.martin@linaro.org>
---
 arch/arm/plat-mxc/ssi-fiq.S |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/arch/arm/plat-mxc/ssi-fiq.S b/arch/arm/plat-mxc/ssi-fiq.S
index 4ddce56..8397a2d 100644
--- a/arch/arm/plat-mxc/ssi-fiq.S
+++ b/arch/arm/plat-mxc/ssi-fiq.S
@@ -124,6 +124,8 @@ imx_ssi_fiq_start:
 1:
 		@ return from FIQ
 		subs	pc, lr, #4
+
+		.align
 imx_ssi_fiq_base:
 		.word 0x0
 imx_ssi_fiq_rx_buffer:
-- 
1.7.1

                 reply	other threads:[~2010-11-16 13:13 UTC|newest]

Thread overview: [no followups] expand[flat|nested]  mbox.gz  Atom feed

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:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

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

  git send-email \
    --in-reply-to=1289913217-8672-1-git-send-email-dave.martin@linaro.org \
    --to=dave.martin@linaro.org \
    --cc=linux-arm-kernel@lists.infradead.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* 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).