Re: [PATCH] eal/x86: fix build on systems with WAITPKG support

[David Marchand <david.marchand@redhat.com>]

On Mon, Aug 28, 2023 at 9:08 AM David Marchand
<david.marchand@redhat.com> wrote:
>
> Hello Bruce,
>
> On Fri, Aug 25, 2023 at 5:29 PM Bruce Richardson
> <bruce.richardson@intel.com> wrote:
> >
> > When doing a build for a system with WAITPKG support and a modern
> > compiler, we get build errors for the "_umonitor" intrinsic, due to the
> > casting away of the "volatile" on the parameter.
> >
> > ../lib/eal/x86/rte_power_intrinsics.c: In function 'rte_power_monitor':
> > ../lib/eal/x86/rte_power_intrinsics.c:113:22: error: passing argument 1
> > of '_umonitor' discards 'volatile' qualifier from pointer target type
> > [-Werror=discarded-qualifiers]
> >   113 |         _umonitor(pmc->addr);
> >         |                   ~~~^~~~~~
> >
> > We can avoid this issue by using RTE_PTR_ADD(..., 0) to cast the pointer
> > through "uintptr_t" and thereby remove the volatile without warning.
> > We also ensure comments are correct for each leg of the
> > ifdef..else..endif block.
> >
> > Fixes: 60943c04f3bc ("eal/x86: use intrinsics for power management")
> > Cc: roretzla@linux.microsoft.com
> >
> > Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
>
> I'm looking for a system with WAITPKG in the RH lab.. so far, no luck.
> Do you have a way to force-reproduce this issue? Like some compiler
> options forcing support?

Ah.. reproduced with -Dcpu_instruction_set=sapphirerapids

[52/241] Compiling C object lib/librte_eal.a.p/eal_x86_rte_power_intrinsics.c.o
../lib/eal/x86/rte_power_intrinsics.c: In function ‘rte_power_monitor’:
../lib/eal/x86/rte_power_intrinsics.c:113:22: warning: passing
argument 1 of ‘_umonitor’ discards ‘volatile’ qualifier from pointer
target type [-Wdiscarded-qualifiers]
  113 |         _umonitor(pmc->addr);
      |                   ~~~^~~~~~
In file included from
/usr/lib/gcc/x86_64-redhat-linux/11/include/x86gprintrin.h:89,
                 from
/usr/lib/gcc/x86_64-redhat-linux/11/include/immintrin.h:27,
                 from ../lib/eal/x86/include/rte_rtm.h:8,
                 from ../lib/eal/x86/rte_power_intrinsics.c:7:
/usr/lib/gcc/x86_64-redhat-linux/11/include/waitpkgintrin.h:39:18:
note: expected ‘void *’ but argument is of type ‘volatile void *’
   39 | _umonitor (void *__A)
      |            ~~~~~~^~~
[241/241] Linking target lib/librte_ethdev.so.24.0


-- 
David Marchand