[U-Boot] [PATCH] arm: use common instructions applicable to armv7m & other arm archs

Albert ARIBAUD
2016-01-29T17:15:46Z

Hello Vikas,

On Mon, 18 Jan 2016 18:52:57 -0800, Vikas Manocha
<vikas.manocha@st.com> wrote:
> BIC instruction to clear the SP is not allowed in armv7m & is deprecated
> in ARMv6T2 & above. This patch cleans the code by using instructions allowed
> for armv7m as well as other Arm archs.

I am not against this patch, which has merits on its own; but the
commit message above raises a couple of questions.

1. It seems to imply that in the current arch/arm/lib/crt0.S, BIC is
incorrectly being used on sp. However, it is *not*; it is used on r3,
precisely because it cannot be used directly on sp, as the comment
before the bic instruction clearly states. Why does the commit
message raise this non-issue?

2. I could not find any information on BIC being deprecated in
Architecture Reference Manuals of either ArmV7 (section "Deprecated
Features in ARMv7-M", or ARMv6-M (section "Deprecated and Obsolete
Features"). Where does this information come from?

Amicalement,
--
Albert.