On Mon, Aug 28, 2023 at 11:29:05AM +0200, David Marchand wrote:
> On Fri, Aug 25, 2023 at 5:29 PM Bruce Richardson
> <bruce.richard...@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.
>
> As Morten, I prefer an explicit cast (keeping your comments) as it
> seems we are exploiting an implementation detail of RTE_PTR_ADD.
>
Ok, I'll do a respin with explicit cast.
>
> > We also ensure comments are correct for each leg of the
> > ifdef..else..endif block.
>
> Thanks.. I had fixed other places but I have missed this one.
>
>
> >
> > Fixes: 60943c04f3bc ("eal/x86: use intrinsics for power management")
> > Cc: roret...@linux.microsoft.com
> >
> > Signed-off-by: Bruce Richardson <bruce.richard...@intel.com>
> > ---
> > lib/eal/x86/rte_power_intrinsics.c | 12 ++++++------
> > 1 file changed, 6 insertions(+), 6 deletions(-)
> >
> > diff --git a/lib/eal/x86/rte_power_intrinsics.c
> > b/lib/eal/x86/rte_power_intrinsics.c
> > index 4066d1392e..4f0404bfb8 100644
> > --- a/lib/eal/x86/rte_power_intrinsics.c
> > +++ b/lib/eal/x86/rte_power_intrinsics.c
> > @@ -103,15 +103,15 @@ rte_power_monitor(const struct rte_power_monitor_cond
> > *pmc,
> > rte_spinlock_lock(&s->lock);
> > s->monitor_addr = pmc->addr;
> >
> > - /*
> > - * we're using raw byte codes for now as only the newest compiler
> > - * versions support this instruction natively.
> > - */
> > -
> > /* set address for UMONITOR */
> > #if defined(RTE_TOOLCHAIN_MSVC) || defined(__WAITPKG__)
> > - _umonitor(pmc->addr);
> > + /* use RTE_PTR_ADD to cast away "volatile" when using the intrinsic
> > */
> > + _umonitor(RTE_PTR_ADD(pmc->addr, 0));
> > #else
> > + /*
> > + * we're using raw byte codes for compiler versions which
> > + * don't support this instruction natively.
> > + */
> > asm volatile(".byte 0xf3, 0x0f, 0xae, 0xf7;"
> > :
> > : "D"(pmc->addr));
>
> Tested-by: David Marchand <david.march...@redhat.com>
>
> An additional question, would Intel CI catch such issue?
> Or was it caught only because you are blessed with bleeding edge hw? :-)
>
Not sure. I would hope so, though.
/Bruce
