linux-kernel - Re: [PATCH] USB: ehci: use packed, aligned(4) instead of removing the packed attribute

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <201106202214.00998.arnd@arndb.de>
Date:	Mon, 20 Jun 2011 22:14:00 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	"Russell King - ARM Linux" <linux@....linux.org.uk>
Cc:	Nicolas Pitre <nico@...xnic.net>,
	Alan Stern <stern@...land.harvard.edu>, gregkh@...e.de,
	linux-usb@...r.kernel.org, lkml <linux-kernel@...r.kernel.org>,
	Rabin Vincent <rabin@....in>,
	Alexander Holler <holler@...oftware.de>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] USB: ehci: use packed, aligned(4) instead of removing the packed attribute

On Monday 20 June 2011 21:32:13 Russell King - ARM Linux wrote:
> > Here the d member is not naturally aligned.  On most architectures, 
> > including ARM with the ABI currently in use, the compiler would insert a 
> > 32-bit padding between c and d.
> 
> And if 'struct foo' represents a structure in device memory, the end
> result is highly unpredicable whether or not you have padding or
> accessors to load 'd' there.  So, you would not have such a structure
> describing a data structure in memory returned by ioremap().

Right.

> Now, the real question is: is there any architecture which is (or may
> be) supported by the Linux kernel which would add padding to:
> 
> struct foo {
>         u8 a;
>         u8 b;
>         u16 c;
>         u32 d;
>         u64 e;
> };

This is the other issue, which we were facing in the scsi drivers.
If an architecture requires padding because some members require
larger than natural alignment here, the 'packed' should be applied
to that member, in order to change the alignment of that member.

	Arnd
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/