From: "Alex Bennée" <alex.bennee@linaro.org>
To: Richard Henderson <rth@twiddle.net>
Cc: peter.maydell@linaro.org, qemu-devel@nongnu.org, aurelien@aurel32.net
Subject: Re: [Qemu-devel] [PATCH 1/8] exec-all.h: Use stl_p to avoid undefinedbehaviour patching x86 jumpss
Date: Tue, 01 Apr 2014 13:09:17 +0100 [thread overview]
Message-ID: <87mwg5s13m.fsf@linaro.org> (raw)
In-Reply-To: <1396052834-26834-2-git-send-email-rth@twiddle.net>
Richard Henderson <rth@twiddle.net> writes:
> From: Peter Maydell <peter.maydell@linaro.org>
>
> The code which patches x86 jump instructions assumes it can do an
> unaligned write of a uint32_t. This is actually safe on x86, but it's
> still undefined behaviour. We have infrastructure for doing efficient
> unaligned accesses which doesn't engage in undefined behaviour, so
> use it.
>
> This is technically fractionally less efficient, at least with gcc 4.6;
> instead of one instruction:
> 7b2: 89 3e mov %edi,(%rsi)
> we get an extra spurious store to the stack slot:
> 7b2: 89 7c 24 64 mov %edi,0x64(%rsp)
> 7b6: 89 3e mov %edi,(%rsi)
Ehh? Is that gcc just being silly and putting parameters for an inline
on the stack frame?
>
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> Signed-off-by: Richard Henderson <rth@twiddle.net>
<snip>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
--
Alex Bennée
next prev parent reply other threads:[~2014-04-01 12:08 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-03-29 0:27 [Qemu-devel] [PATCH 0/8] tcg: tidy the type of code_ptr Richard Henderson
2014-03-29 0:27 ` [Qemu-devel] [PATCH 1/8] exec-all.h: Use stl_p to avoid undefined behaviour patching x86 jumps Richard Henderson
2014-04-01 12:09 ` Alex Bennée [this message]
2014-04-01 12:18 ` [Qemu-devel] [PATCH 1/8] exec-all.h: Use stl_p to avoid undefinedbehaviour patching x86 jumpss Peter Maydell
2014-03-29 0:27 ` [Qemu-devel] [PATCH 2/8] tcg: Avoid stores to unaligned addresses Richard Henderson
2014-04-01 12:12 ` Alex Bennée
2014-03-29 0:27 ` [Qemu-devel] [PATCH 3/8] tcg: Avoid undefined behaviour patching code at " Richard Henderson
2014-04-01 12:13 ` [Qemu-devel] [PATCH 3/8] tcg: Avoid undefined behaviour patchingcode at unaligned addressess Alex Bennée
2014-03-29 0:27 ` [Qemu-devel] [PATCH 4/8] tcg: Define tcg_itype for code pointers Richard Henderson
2014-03-29 0:27 ` [Qemu-devel] [PATCH 5/8] tcg-ppc64: Define TCG_TARGET_ITYPE_SIZE Richard Henderson
2014-03-29 0:27 ` [Qemu-devel] [PATCH 6/8] tcg-ppc: " Richard Henderson
2014-03-29 0:27 ` [Qemu-devel] [PATCH 7/8] tcg-aarch64: " Richard Henderson
2014-03-29 0:27 ` [Qemu-devel] [PATCH 8/8] tcg-sparc: " Richard Henderson
2014-03-29 20:26 ` [Qemu-devel] [PATCH 0/8] tcg: tidy the type of code_ptr Peter Maydell
2014-03-30 15:31 ` Richard Henderson
2014-03-31 3:19 ` Richard Henderson
2014-04-01 12:05 ` Alex Bennée
2014-04-01 12:19 ` Alex Bennée
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=87mwg5s13m.fsf@linaro.org \
--to=alex.bennee@linaro.org \
--cc=aurelien@aurel32.net \
--cc=peter.maydell@linaro.org \
--cc=qemu-devel@nongnu.org \
--cc=rth@twiddle.net \
/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).