Re: [dpdk-dev] [PATCH v3 08/10] eal/windows: fix rte_page_sizes with Clang on Windows

[Dmitry Kozlyuk <dmitry.kozliuk@gmail.com>]

> On Wed, Apr 15, 2020 at 4:02 PM Dmitry Kozlyuk <dmitry.kozliuk@gmail.com> wrote:
> >  
> > > On Wed, Apr 15, 2020 at 1:16 AM Dmitry Kozlyuk <dmitry.kozliuk@gmail.com> wrote:  
> > > >
> > > > Clang on Windows follows MS ABI where enum values are limited to 2^31-1.
> > > > Enum rte_page_size has members valued above this limit, which get
> > > > wrapped to zero, resulting in compilation error (duplicate values in
> > > > enum). Using MS ABI is mandatory for Windows EAL to call Win32 APIs.
> > > >
> > > > Define these values outside of the enum for Clang on Windows only.
> > > > This does not affect runtime, because Windows doesn't run on machines
> > > > with 4GiB and 16GiB hugepages.
> > > >
> > > > Signed-off-by: Dmitry Kozlyuk <dmitry.kozliuk@gmail.com>
> > > > ---
> > > >  lib/librte_eal/include/rte_memory.h | 6 ++++++
> > > >  1 file changed, 6 insertions(+)
> > > >
> > > > diff --git a/lib/librte_eal/include/rte_memory.h b/lib/librte_eal/include/rte_memory.h
> > > > index 1b7c3e5df..3ec673f51 100644
> > > > --- a/lib/librte_eal/include/rte_memory.h
> > > > +++ b/lib/librte_eal/include/rte_memory.h
> > > > @@ -34,8 +34,14 @@ enum rte_page_sizes {
> > > >         RTE_PGSIZE_256M  = 1ULL << 28,
> > > >         RTE_PGSIZE_512M  = 1ULL << 29,
> > > >         RTE_PGSIZE_1G    = 1ULL << 30,
> > > > +/* Work around Clang on Windows being limited to 32-bit underlying type. */  
> > >
> > > It does look like "enum rte_page_sizes" NOT used as enum anywhere.
> > >
> > > [master][dpdk.org] $ grep -ri "enum rte_page_sizes" lib/
> > > lib/librte_eal/include/rte_memory.h:enum rte_page_sizes {
> > >
> > > Why not remove this workaround and define all items as #define to
> > > avoid below ifdef clutter.
> > >  
> > > > +#if !defined(RTE_CC_CLANG) || !defined(RTE_EXEC_ENV_WINDOWS)  
> > >
> > > See above.
> > >  
> > > >         RTE_PGSIZE_4G    = 1ULL << 32,
> > > >         RTE_PGSIZE_16G   = 1ULL << 34,
> > > > +#else
> > > > +#define RTE_PGSIZE_4G  (1ULL << 32)
> > > > +#define RTE_PGSIZE_16G (1ULL << 34)
> > > > +#endif
> > > >  };
> > > >
> > > >  #define SOCKET_ID_ANY -1                    /**< Any NUMA socket. */
> > > > --
> > > > 2.25.1
> > > >  
> >
> > This is a public header and removing enum rte_page_sizes will break API.
> > Moving members out of enum while keeping enum itself might break compilation
> > because of integer constants being converted to enum (with -Werror).  
> 
> If none of the public API is using this enum then I think, we may not
> need to make this enum as public.

Agreed.

> Since it has ULL, I believe both cases(enum or define), it will be
> treated as unsigned long long. ie. NO ABI breakage.

I was talking about API only (compile-time compatibility). Getting rid of
#ifdef and workarounds sounds right, we'll just need a notice in release
notes.

-- 
Dmitry Kozlyuk