linux-kernel - RE: [PATCH] um: don't use CONFIG_X86

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Date:   Fri, 3 Sep 2021 08:27:24 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Johannes Berg' <johannes@...solutions.net>,
        "linux-um@...ts.infradead.org" <linux-um@...ts.infradead.org>
CC:     "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Johannes Berg <johannes.berg@...el.com>
Subject: RE: [PATCH] um: don't use CONFIG_X86_{32,64} symbols on x86

From: Johannes Berg
> Sent: 02 September 2021 09:28
> 
> The CONFIG_X86_32 and CONFIG_X86_64 symbols are used by
> both "real" x86 architecture builds and ARCH=um today.
> However, clearly most people and places in the code are
> treating it as the architecture Kconfig (technically
> that's just CONFIG_X86) and use it to indicate that the
> architecture is X86 in 32- or 64-bit flavour.
> 
> This has caused a fair amount of issues in the past,
> for example drivers not building because use x86 macros
> or similar under CONFIG_X86_{32,64} ifdef, and then we
> find build reports and add "!UML" to their Kconfig etc.
> 
> However, this is error-prone and a kind of whack-a-mole
> game, even with the build bots reporting things.

I suspect you've just changed the 'mole'.

You've now got lots of lines like:

#if defined(CONFIG_X86_64) || defined(CONFIG_X86_64_UML)

Missing off the UML define is going to cause the 32bit code
to get compiled by mistake - which is likely to be more
confusing that the places where you need to do special 'stuff'
for UML.

	David

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