On Tue, 2019-07-09 at 22:04 -0700, Joe Perches wrote:
These GENMASK uses are inverted argument order and the
actual masks produced are incorrect. Fix them.
Add checkpatch tests to help avoid more misuses too.
Joe Perches (12):
checkpatch: Add GENMASK tests
IMHO this doesn't make a lot of sense as a checkpatch test - just throw
in a BUILD_BUG_ON()?
johannes
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On Wed, Jul 10, 2019 at 11:17:31AM +0200, Johannes Berg wrote:
On Tue, 2019-07-09 at 22:04 -0700, Joe Perches wrote:
quoted
These GENMASK uses are inverted argument order and the
actual masks produced are incorrect. Fix them.
Add checkpatch tests to help avoid more misuses too.
Joe Perches (12):
checkpatch: Add GENMASK tests
IMHO this doesn't make a lot of sense as a checkpatch test - just throw
in a BUILD_BUG_ON()?
My personal take on this is that GENMASK() is really not useful, it's
just pure obfuscation and leads to exactly these kinds of mistakes.
Yes, I fully understand the argument that you can just specify the
start and end bits, and it _in theory_ makes the code more readable.
However, the problem is when writing code. GENMASK(a, b). Is a the
starting bit or ending bit? Is b the number of bits? It's confusing
and causes mistakes resulting in incorrect code. A BUILD_BUG_ON()
can catch some of the cases, but not all of them.
For example:
GENMASK(6, 2)
would satisify the requirement that a > b, so a BUILD_BUG_ON() will
not trigger, but was the author meaning 0x3c or 0xc0?
Personally, I've decided I am _not_ going to use GENMASK() in my code
because I struggle to get the macro arguments correct - I'm _much_
happier, and it is way more reliable for me to write the mask in hex
notation.
I think this is where use of a ternary operator would come in use. The
normal way of writing a number of bits tends to be "a:b", so if GENMASK
took something like GENMASK(6:2), then I'd have less issue with it,
because it's argument is then in a familiar notation.
Yes, I'm sure that someone will point out that the GENMASK arguments
are just in the same order, but that doesn't prevent _me_ frequently
getting it wrong - and that's the point. The macro seems to me to
cause more problems than it solves.
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On Wed, 2019-07-10 at 10:43 +0100, Russell King - ARM Linux admin wrote:
On Wed, Jul 10, 2019 at 11:17:31AM +0200, Johannes Berg wrote:
quoted
On Tue, 2019-07-09 at 22:04 -0700, Joe Perches wrote:
quoted
These GENMASK uses are inverted argument order and the
actual masks produced are incorrect. Fix them.
Add checkpatch tests to help avoid more misuses too.
Joe Perches (12):
checkpatch: Add GENMASK tests
IMHO this doesn't make a lot of sense as a checkpatch test - just throw
in a BUILD_BUG_ON()?
I tried that.
It'd can't be done as it's used in declarations
and included in asm files and it uses the UL()
macro.
I also tried just making it do the right thing
whatever the argument order.
Oh well.
My personal take on this is that GENMASK() is really not useful, it's
just pure obfuscation and leads to exactly these kinds of mistakes.
Yes, I fully understand the argument that you can just specify the
start and end bits, and it _in theory_ makes the code more readable.
However, the problem is when writing code. GENMASK(a, b). Is a the
starting bit or ending bit? Is b the number of bits? It's confusing
and causes mistakes resulting in incorrect code. A BUILD_BUG_ON()
can catch some of the cases, but not all of them.
It's a horrid little macro and I agree with Russell.
I also think if it existed at all it should have been
GENMASK(low, high) not GENMASK(high, low).
I
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On Wed, 2019-07-10 at 08:45 -0700, Joe Perches wrote:
On Wed, 2019-07-10 at 10:43 +0100, Russell King - ARM Linux admin wrote:
quoted
On Wed, Jul 10, 2019 at 11:17:31AM +0200, Johannes Berg wrote:
quoted
On Tue, 2019-07-09 at 22:04 -0700, Joe Perches wrote:
quoted
These GENMASK uses are inverted argument order and the
actual masks produced are incorrect. Fix them.
Add checkpatch tests to help avoid more misuses too.
Joe Perches (12):
checkpatch: Add GENMASK tests
IMHO this doesn't make a lot of sense as a checkpatch test - just throw
in a BUILD_BUG_ON()?
I tried that.
It'd can't be done as it's used in declarations
and included in asm files and it uses the UL()
macro.
I also tried just making it do the right thing
whatever the argument order.
I forgot.
I also made all those arguments when it was
introduced in 2013.
https://lore.kernel.org/patchwork/patch/414248/
Oh well.
yeah.
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