[U-Boot] [PATCH v2] arm: Switch to -mno-unaligned-access when supported by the compiler

Måns Rullgård
2014-02-10T15:40:53Z

M?ns Rullg?rd <mans@mansr.com> writes:

> Albert ARIBAUD <albert.u.boot@aribaud.net> writes:
>
>> Hi Tom,
>>
>> On Mon, 10 Feb 2014 08:21:39 -0500, Tom Rini <trini@ti.com> wrote:
>>
>>> On Mon, Feb 10, 2014 at 10:24:47AM +0100, Albert ARIBAUD wrote:
>>> > Hi Tom,
>>> >
>>> > On Tue, 4 Feb 2014 12:05:33 -0500, Tom Rini <trini@ti.com> wrote:
>>> >
>>> > > When we tell the compiler to optimize for ARMv7 it assumes a default of
>>> > > unaligned accesses being supported at the hardware level and can make
>>> > > use of this to perform what it deems as an optimization in any case,
>>> > > including allowing for data to become unaligned. We explicitly disallow
>>> > > this hardware feature so we must tell the compiler.
>>> > >
>>> > > Cc: Albert ARIBAUD <albert.u.boot@aribaud.net>
>>> > > Cc: Mans Rullgard <mans@mansr.com>
>>> > > Signed-off-by: Tom Rini <trini@ti.com>
>>> >
>>> > NAK -- the discrepancy between the compiler being told to allow native
>>> > unaligned accesses while at the same time telling the hardware to trap
>>> > them is conscious and voluntary. It was chosen to help detect unaligned
>>> > accesses which are rarely necessary and can be explicitly performed by
>>> > software on a case by case basis.
>>> >
>>> > If and when a specific file requires unaligned access which cannot be
>>> > made by some other mean than enabling -mno-unaligned-access, then this
>>> > file should have it added, not the whole of U-Boot.
>>>
>>> Right, I recall the discussion, and we chose wrong.
>>
>> I am quite prepared to discuss whether we chose wrong or right, and
>> to change my mind when the conditions are right, but I'll need more than
>> such a short and simple statement. :)
>
> I already gave you a detailed explanation some months ago. You refused
> to read it.

For reference: http://article.gmane.org/gmane.comp.boot-loaders.u-boot/171876

--
M?ns Rullg?rd
mans at mansr.com