Re: [PATCH v3 04/23] linux/net.h: use unique identifier for each struct _ddebug

[Rasmus Villemoes]

On 10/11/2018 00.22, Joe Perches wrote:
> On Sat, 2018-11-10 at 00:10 +0100, Rasmus Villemoes wrote:
>> Changes on x86-64 later in this series require that all struct _ddebug
>> descriptors in a translation unit uses distinct identifiers. Realize
>> that for net_dbg_ratelimited by generating such an identifier via
>> __UNIQUE_ID and pass that to an extra level of macros.
>>
>> No functional change.
> 
> Why does this require an extra indirection _<macro>?
> 

Because the identifier used in the

>>  	DEFINE_DYNAMIC_DEBUG_METADATA(descriptor, fmt);

line must be the same as the one in the

>>  	if (DYNAMIC_DEBUG_BRANCH(descriptor) &&	

line. That identifier used to be simply "descriptor", with C scope rules
making that ok. But because of the asm games I'm playing later, I need
to generate a fresh identifier for each instance. That identifier must
be referenced in two places in the C source - hence the need to use an
extra level of macros to have the __UNIQUE_ID() expanded before
_net_dbg_ratelimited gets expanded.

More or less every use of __UNIQUE_ID requires such an extra level
(because one very rarely needs to use an identifier exactly once - the
point of giving stuff a name is to refer to it again.)

Rasmus