[Mesa-dev] [PATCH] st/mesa: init hash keys with memset(), not designated initializers

[Roland Scheidegger]

Am 12.03.19 um 18:34 schrieb Eric Anholt:
> Ilia Mirkin <imirkin at alum.mit.edu> writes:
> 
>> I believe the distinction here is between initializing all the fields
>> and using them individually (thus leaving the padding uninitialized),
>> vs using the fields to create a structure to hash as a sequence of
>> bytes. For the latter, you really need all the memory initialized, not
>> just the "valid" parts of the structure. In at least my mind, it's
>> fairly well-established that compilers don't always initialize all of
>> a structure's underlying bytes, but I also don't have a specific
>> instance of that situation I can point to.
>>
>> For most usage, foo = {0} is fine since you're not hashing the bytes
>> but rather accessing the fields directly. But for hashing, you really
>> want all the bits initialized.
> 
> Gah.  The commit message even said it was about padding, and I failed to
> read.  Sorry for the noise, this does seem right.

The alternative is to use explicit padding in the struct, so that
structure initialization is guaranteed to initialize everything to zero.
I believe some places still do that too, but it's not very nice neither
(can easily make mistakes there). So - pick your poison...

Roland

> 
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