On Tuesday 19 May 2015 23:07:21 Russell King - ARM Linux wrote:
> If you look carefully at this, you'll notice that it's utter crap.
> (Sorry, but it is.) It has two problems:
>
> 1. It'll never match a Cortex-A9 CPU. Cortex-A9 has a MIDR value of
> 0x412fc09a, not 0x00000c09. The bit position of the part number
> field isn't even right.
>
> 2. If it does match, then we branch to "v7_invalidate_l1" without setting
> the link register: we'll never return back here (we'll return to whatever
> random value the link register contains) and so we'll never make it to
> secondary_startup. *Thankfully*, because of (1), this branch will
> never be taken - this is it's saving grace.
Yes, I've understood both before.
> Your patch introduces a /third/ form of crapiness:
>
> 3. If the PSR happens to have Z=1, the "beq" instruction will be taken,
> thereby crashing the system because of (2).
Right, this was the result of sloppiness on my side when fat-fingering
a patch for illustration.
> The /simplest/ change which would fix this problem is to just change
> proc-v7.S. The remainder is effectively a cleanup removing redundant
> code.
Fair enough. I wasn't sure if we're confident enough about that
change already to put it into stable backports. If the risk is low
enough, that's fine.
Arnd
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