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SubjectRe: [PATCH v3 7/7] dynamic_debug: add jump label support
On 07/08/2016 05:41 PM, Andrew Morton wrote:
> On Wed, 6 Jul 2016 17:42:36 -0400 Jason Baron <> wrote:
>> Although dynamic debug is often only used for debug builds, sometimes its
>> enabled for production builds as well. Minimize its impact by using jump
>> labels. This reduces the text section by 7000+ bytes in the kernel image
>> below. It does increase data, but this should only be referenced when
>> changing the direction of the branches, and hence usually not in cache.
>> ...
>> +#ifdef HAVE_JUMP_LABEL
>> +
>> +#define dd_key_init(key, init) key = (init)
>> ...
>> +#else
>> +
>> +#define dd_key_init(key, init)
>> +
> umm, lazy. One is an lval and returns a value and the other does
> neither. Lack of parenthesization in the first version doubtless
> exposes various horrors.
> Care to do something more robust and conventional here? Presumably use
> symmetrical do{}while(0) things, neither of which is an lval, both of
> which don't return anything.


The 'dd_key_init()' macro is being used here to help initialize
the 'key' field in the 'struct _ddebug', and its not being used as a

In the 'HAVE_JUMP_LABEL' case, we are initializing the 'key' field, while in
the not-'HAVE_JUMP_LABEL' case, the 'key' field is simply not present
in the structure (to conserve space).



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