From: Mark Rutland
Sent: 24 May 2021 13:29
On Mon, May 24, 2021 at 12:46:26PM +0100, Christoph Hellwig wrote:
quoted
On Thu, May 20, 2021 at 03:43:37AM -0700, Joe Richey wrote:
quoted
This patch series changes all UAPI uses of BIT() to just be open-coded.
However, there really should be a check for this in checkpatch.pl
Currently, the script actually _encourages_ users to use the BIT macro
even if adding things to UAPI.
Yes. In fact it should warn about BIT() in general. It is totally
pointless obsfucation that doesn't even save any typing at all.
That's not quite true; the point is that if you use BIT() consistently,
then even when you refer to bits 32 to 63 you won't accidentally
introduce shifts of more than the width of int, and the definition will
work equally well for assembly and C, which isn't true if you use `1UL`
in the definition.
With that in mind it's shorter and clearer than its functional
equivalent:
BIT(x)
(UL(1) << (x))
So IMO it's preferable to use BIT() generally, or _BITUL() in uapi
headers.
And then, suddenly the compiler warns about truncation of the
high bits when ~BIT(x) is used to mask a 32bit value on 64bit systems.
Once the C standard committee had decided to change from K&R's
'sign preserving' integer promotions to 'value preserving'
you always lose somewhere.
Personally I prefer hex constants - I can't count bits at all.
David
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