Re: [RFC PATCH 6/9] memory: apple: Add apple-mcc driver to manage MCC perf in Apple SoCs

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On 14/10/2021 17.04, Krzysztof Kozlowski wrote:
It is; only modules with a GPL-compatible MODULE_LICENSE get to use
symbols exported via EXPORT_SYMBOL_GPL.

Although there might be such correlation but it's not a rule. You can
have a GPL module exporting symbols without GPL requirement
(EXPORT_SYMBOLS). You can have a GPL+MIT module exporting symbols as
GPL. Obviously you cannot have a non-GPL module, as we do not accept
these and there is no such choice.

What I mean is that modules can only import GPL symbols if they themselves are GPL compatible. What I didn't know is that "Dual MIT/GPL" is a valid string for MODULE_LICENSE to qualify as such.

See kernel/module.c for the symbol lookup logic and
include/linux/license.h for the logic to check the string (seems like
"Dual MIT/GPL" is explicitly whitelisted there).

Not related to export symbol. It is used for determining the tainted
kernel via other licenses.


Not just that; that module taint is used as a filter so that non-GPL-compatible modules are technically prevented from resolving EXPORT_SYMBOL_GPL symbols.

Of course, this is a futile effort, as ~every time I see a proprietary
module in some embedded device, it either falsely declares itself to be
GPL, or they have a shim module that re-exports GPL symbols as non-GPL.


This is being removed soon (or already).

? Good luck getting proprietary embedded vendors to start following licenses... :)

--
Hector Martin (marcan@xxxxxxxxx)
Public Key: https://mrcn.st/pub



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