Messages in this thread | | | Date | Wed, 23 Feb 2022 16:45:27 -0800 | Subject | Re: [PATCH v4] hwmon: (dell-smm) Improve assembly code | From | Guenter Roeck <> |
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On 2/23/22 14:35, David Laight wrote: > From: Armin Wolf >> Sent: 23 February 2022 21:39 > ... >>> As far as this patch goes I think I'd add a 'stc' (set carry) >>> instruction before the first 'outb'. >>> Then if the 'something magic happens here' doesn't happen (because >>> you aren't on the right kind of motherboard) the action fails. >>> >>> David >> >> We already check for such scenarios by checking if eax changed. >> I would not set the carry flag before doing a SMM call since im >> not sure if the firmware code always clears the carry flag when >> the call was successful. >> If for example the firmware code only sets the carry flag on >> error and otherwise ignores the carry flag, we might create some >> false negatives when a successful SMM call leaves the carry flag set. > > If you are worried about that you should be clearing carry on entry. >
I agree, but now we have an argument for clearing carry (because the SMM code might not do it) and for setting carry (because the SMM code might not execute). I don't know which way to go, if any, but that would be a functional change and should be submitted as separate patch.
Guenter
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