[PATCH] ARM: Do not allow unaligned accesses when CONFIG_ALIGNMENT_TRAP
From: catalin.marinas@arm.com (Catalin Marinas)
Date: 2011-05-23 14:41:53
2011/5/23 M?ns Rullg?rd [off-list ref]:
Catalin Marinas [off-list ref] writes:quoted
On Mon, 2011-05-23 at 14:21 +0100, Russell King - ARM Linux wrote:quoted
On Mon, May 23, 2011 at 12:16:48PM +0100, Catalin Marinas wrote:quoted
Newer versions of gcc generate unaligned accesses by default, causing kernel panics when CONFIG_ALIGNMENT_TRAP is enabled. This patch adds the -mno-unaligned-access option to gcc.This description doesn't make sense. ?If we have alignment traps enabled, then we _expect_ to fix up unaligned loads and stores. Therefore there should be no panic if CONFIG_ALIGNMENT_TRAP is enabled. So what's the _actual_ problem that this is trying to address? ?What's the panic/oops look like? ?And that information should be in the commit description _anyway_.OK, not clear from my commit log. See below for details (I'll add them to the log): http://www.codesourcery.com/archives/arm-gnu/msg04202.html Basically the fault happens before we call alignment_init(). There are other ways to fix this issue (like initialising the alignment handler earlier).The reset value of SCTLR.A is 0 on ARMv7. ?Something must be setting it to 1 early, before the alignment trap handler is initialised. ?This something is what needs to be changed.
It is set to 1 in __enable_mmu in head.S. -- Catalin