C preprocessor

[zeusk]

In my OS, SPINLOCK_DECLARE depends on whether the build is SMP or not, when it's for UP, the macro expands to nothing so if i have something like

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static SPINLOCK_DECLARE(blah_blah);

Compiler gives me an error about expecting an identifier/type before ';' Is there a better way to fix this besides having to write a new macro like DECLARE_STATIC_SPINLOCK ?

[iansjack]

Isn't this what #ifdef/#endif sections are intended for?

[bluemoon]

Is there a better way to fix this besides having to write a new macro like DECLARE_STATIC_SPINLOCK ?

Yes, do not use macro, and properly define a data-type for it, and you get type-checking for free.

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typedef volatile uint32_t _SPINLOCK __attribute__ ((aligned(16)));

And you macro the function to {empty} instead - but wait, even for single processor a normal spinlock is not empty.

EDIT: Usually, the multi-processor version runs just fine on uni-processor, and unless you care that extra nano-second you may just use MP version and reduce maintanence effort.

[zeusk]

Yes, do not use macro, and properly define a data-type for it, and you get type-checking for free.

Code: Select all

typedef volatile uint32_t _SPINLOCK __attribute__ ((aligned(16)));

And you macro the function to {empty} instead - but wait, even for single processor a normal spinlock is not empty.

EDIT: Usually, the multi-processor version runs just fine on uni-processor, and unless you care that extra nano-second you may just use MP version and reduce maintanence effort.

I'm actually working on an embedded ARM kernel, which will run on high-end devices (1GHz QSD8650b with 576M Ram) to low-end devices (48MHz Cortex-M0 with 8K RAM, besides no MMU ... Good old 90s). I cannot waste those precious 4 bytes.

[JamesM]

In my OS, SPINLOCK_DECLARE depends on whether the build is SMP or not, when it's for UP, the macro expands to nothing so if i have something like

Code: Select all

static SPINLOCK_DECLARE(blah_blah);

Compiler gives me an error about expecting an identifier/type before ';' Is there a better way to fix this besides having to write a new macro like DECLARE_STATIC_SPINLOCK ?

Having a separate declarator for static spinlocks seems like the only real way to me.

[evoex]

I reckon this would be optimized away completely by most compilers (actually, I'm not sure how any compiler would make it do anything), and should work for both static and non-static:

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#define SPINLOCK_DECLARE(x) struct {} x

Hope that helps.