Re: [dpdk-dev] [PATCH v3] Fix two compile issues with i686 platform

[Neil Horman <nhorman@tuxdriver.com>]

On Fri, Dec 05, 2014 at 03:02:33PM +0000, Bruce Richardson wrote:
> On Fri, Dec 05, 2014 at 09:22:05AM -0500, Neil Horman wrote:
> > On Fri, Dec 05, 2014 at 04:31:47PM +0800, Chao Zhu wrote:
> > > 
> > > On 2014/12/4 17:12, Michael Qiu wrote:
> > > >lib/librte_eal/linuxapp/eal/eal_memory.c:324:4: error: comparison
> > > >is always false due to limited range of data type [-Werror=type-limits]
> > > >     || (hugepage_sz == RTE_PGSIZE_16G)) {
> > > >     ^
> > > >cc1: all warnings being treated as errors
> > > >
> > > >lib/librte_eal/linuxapp/eal/eal.c(461): error #2259: non-pointer
> > > >conversion from "long long" to "void *" may lose significant bits
> > > >    RTE_PTR_ALIGN_CEIL((uintptr_t)addr, RTE_PGSIZE_16M);
> > > >
> > > >This was introuduced by commit b77b5639:
> > > >         mem: add huge page sizes for IBM Power
> > > >
> > > >The root cause is that size_t and uintptr_t are 32-bit in i686
> > > >platform, but RTE_PGSIZE_16M and RTE_PGSIZE_16G are always 64-bit.
> > > >
> > > >Define RTE_PGSIZE_16G only in 64 bit platform to avoid
> > > >this issue.
> > > >
> > > >Signed-off-by: Michael Qiu <michael.qiu@intel.com>
> > > >---
> > > >  v3 ---> v2
> > > >	Change RTE_PGSIZE_16G from ULL to UL
> > > >	to keep all entries consistent
> > > >
> > > >  V2 ---> v1
> > > >	Change two type entries to one, and
> > > >	leave RTE_PGSIZE_16G only valid for
> > > >	64-bit platform
> > > >
> > NACK, this is the wrong way to fix this problem.  Pagesizes are independent of
> > architecutre.  While a system can't have a hugepage size that exceeds its
> > virtual address limit, theres no need to do per-architecture special casing of
> > page sizes here.  Instead of littering the code with ifdef RTE_ARCH_64
> > everytime you want to check a page size, just convert the size_t to a uint64_t
> > and you can allow all of the enumerated page types on all architecutres, and
> > save yourself some ifdeffing in the process.
> > 
> > Neil
> 
> While I get your point, I find it distasteful to use a uint64_t for memory sizes,
> when there is the size_t type defined for that particular purpose.
> However, I suppose that reducing the number of #ifdefs compared to using the
> "correct" datatypes for objects is a more practical optino - however distastful
> I find it.

size_t isn't defined for memory sizes in the sense that we're using them here.
size_t is meant to address the need for a type to describe object sizes on a
particular system, and it itself is sized accordingly (32 bits on a 32 bit arch,
64 on 64), so that you can safely store a size that the system in question might
maximally allocate/return.  In this situation we are describing memory sizes
that might occur no a plurality of arches, and so size_t is inappropriate
because it as a type is not sized for anything other than the arch it is being
built for.  The pragmatic benefits of ennumerating page sizes in a single
canonical location far outweigh the desire to use a misappropriated type to
describe them.

Neil