[dpdk-dev] [PATCH v3 1/2] eal: add API to align integer to previous power of 2

[Matan Azrad]

Hi Pavan

From: Pavan Nikhilesh, Wednesday, April 4, 2018 9:36 PM
> On Wed, Apr 04, 2018 at 06:23:19PM +0000, Matan Azrad wrote:
> > Hi Pavan
> >
> > From: Pavan Nikhilesh, Wednesday, April 4, 2018 9:16 PM
> > > Hi Matan,
> > >
> > > >
> > > > Got you.
> > > > Looks like you found issue here...
> > > > The experimental tag probably should be in a root .h file.
> > > > Probably, need a fix patch to move it for a different\new .h file.
> > > >
> > > > What do you think?
> > > >
> > >
> > > Actually thats just start of the rabbit hole, if we succeed to tag a
> > > inline function in rte_common.h as experimental every lib/driver
> > > that uses rte_common.h (almost everything) needs to have CFLAGS set
> > > to - DALLOW_EXPERIMENTAL_API.
> > >
> >
> > Isn't it relevant only for the libs which are using the new tagged APIs?
> 
> Static inline functions in .h files will be added to each and every .c example
> preprocessor output for rte_pci.c which includes rte_common.h:
> 
> # 231 "/home/pavan/Work/clean/dpdk/build/include/rte_common.h"
> extern int RTE_BUILD_BUG_ON_detected_error; # 249
> "/home/pavan/Work/clean/dpdk/build/include/rte_common.h"
> static inline uint32_t __attribute__((deprecated("Symbol is not yet part of
> stable ABI"), section(".text.experimental"))) rte_combine32ms1b(register
> uint32_t x) {  x |= x >> 1;  x |= x >> 2;  x |= x >> 4;  x |= x >> 8;  x |= x >> 16;
> 
>  return x;
> }
> # 271 "/home/pavan/Work/clean/dpdk/build/include/rte_common.h"
> static inline uint64_t
> rte_combine64ms1b(register uint64_t v)
> {
>  v |= v >> 1;
>  v |= v >> 2;
>  v |= v >> 4;
>  v |= v >> 8;
>  v |= v >> 16;
>  v |= v >> 32;
> 
>  return v;
> }
> 
> Which causes compiler to throw error as DALLOW_EXPERIMENTAL_API is not
> added to cflags.
> 

Are you sure?

I added the next code and the compilation passed:
static inline uint32_t
__attribute__((deprecated("Symbol is not yet part of stable ABI"), \
section(".text.experimental")))
rte_combine32ms1b(register uint32_t x)
{
	x |= x >> 1;
	x |= x >> 2;
	x |= x >> 4;
	x |= x >> 8;
	x |= x >> 16;

	return x;
}

Actually, the combine functions should not be experimental (already used in the existed code).
It also will prevent us to add the cflag in every lib which uses the old align functions. 
Only the new align functions should be tagged.
And then, you need to add the cflag only in the places which use these functions.

Am I missing something?

> >
> > > Regards,
> > > Pavan.