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doc: botching-up-ioctls: Make it clearer why structs must be padded

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This came up in discussions when reviewing drm patches.

Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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Daniel Vetter 2018-05-02 09:51:06 +02:00 committed by Jonathan Corbet
parent c9161088e5
commit 1897e8f394
1 changed files with 3 additions and 1 deletions
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4
Documentation/ioctl/botching-up-ioctls.txt
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@ -73,7 +73,9 @@ will have a second iteration or at least an extension for any given interface.
future extensions is going right down the gutters since someone will submit
an ioctl struct with random stack garbage in the yet unused parts. Which
then bakes in the ABI that those fields can never be used for anything else
but garbage.
but garbage. This is also the reason why you must explicitly pad all
structures, even if you never use them in an array - the padding the compiler
might insert could contain garbage.
* Have simple testcases for all of the above.