Messages in this thread Patch in this message | | | Date | Thu, 1 Jun 2023 12:32:38 +0200 | Subject | Re: [PATCH v2 07/12] parisc/percpu: Work around the lack of __SIZEOF_INT128__ | From | Helge Deller <> |
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On 6/1/23 12:14, Peter Zijlstra wrote: > On Wed, May 31, 2023 at 04:21:22PM +0200, Arnd Bergmann wrote: > >> It would be nice to have the hack more localized to parisc >> and guarded with a CONFIG_GCC_VERSION check so we can kill >> it off in the future, once we drop either gcc-10 or parisc >> support. > > I vote for dropping parisc -- it's the only 64bit arch that doesn't have > sane atomics.
Of course I'm against dropping parisc.
> Anyway, the below seems to work -- build tested with GCC-10.1
I don't think we need to care about gcc-10 on parisc. Debian and Gentoo are the only supported distributions, while Debian requires gcc-12 to build > 6.x kernels, and I assume Gentoo uses at least gcc-12 as well.
So raising the gcc limit for parisc only (at least temporarily for now) should be fine and your workaround below wouldn't be necessary, right?
Helge
> --- > Subject: parisc/percpu: Work around the lack of __SIZEOF_INT128__ > From: Peter Zijlstra <peterz@infradead.org> > Date: Tue May 30 22:27:40 CEST 2023 > > HPPA64 is unique in not providing __SIZEOF_INT128__ across all > supported compilers, specifically it only started doing this with > GCC-11. > > Since the per-cpu ops are universally availably, and > this_cpu_{,try_}cmpxchg128() is expected to be available on all 64bit > architectures a wee bodge is in order. > > Sadly, while C reverts to memcpy() for assignment of POD types, it does > not revert to memcmp() for for equality. Therefore frob that manually. > > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > --- > arch/parisc/include/asm/percpu.h | 77 +++++++++++++++++++++++++++++++++++++++ > 1 file changed, 77 insertions(+) > > --- /dev/null > +++ b/arch/parisc/include/asm/percpu.h > @@ -0,0 +1,77 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > +#ifndef _ASM_PARISC_PERCPU_H > +#define _ASM_PARISC_PERCPU_H > + > +#include <linux/types.h> > + > +#if defined(CONFIG_64BIT) && CONFIG_GCC_VERSION < 1100000 > + > +/* > + * GCC prior to 11 does not provide __SIZEOF_INT128__ on HPPA64 > + * as such we need to provide an alternative implementation of > + * {raw,this}_cpu_{,try_}cmpxchg128(). > + * > + * This obviously doesn't function as u128 should, but for the purpose > + * of per-cpu cmpxchg128 it might just do. > + */ > +typedef struct { > + u64 a, b; > +} u128 __attribute__((aligned(16))); > + > +#define raw_cpu_generic_try_cmpxchg_memcmp(pcp, ovalp, nval) \ > +({ \ > + typeof(pcp) *__p = raw_cpu_ptr(&(pcp)); \ > + typeof(pcp) __val = *__p, __old = *(ovalp); \ > + bool __ret; \ > + if (!__builtin_memcmp(&__val, &__old, sizeof(pcp))) { \ > + *__p = nval; \ > + __ret = true; \ > + } else { \ > + *(ovalp) = __val; \ > + __ret = false; \ > + } \ > + __ret; \ > +}) > + > +#define raw_cpu_generic_cmpxchg_memcmp(pcp, oval, nval) \ > +({ \ > + typeof(pcp) __old = (oval); \ > + raw_cpu_generic_try_cmpxchg_memcpy(pcp, &__old, nval); \ > + __old; \ > +}) > + > +#define raw_cpu_cmpxchg128(pcp, oval, nval) \ > + raw_cpu_generic_cmpxchg_memcmp(pcp, oval, nval) > +#define raw_cpu_try_cmpxchg128(pcp, ovalp, nval) \ > + raw_cpu_generic_try_cmpxchg_memcmp(pcp, ovalp, nval) > + > +#define this_cpu_generic_try_cmpxchg_memcmp(pcp, ovalp, nval) \ > +({ \ > + bool __ret; \ > + unsigned long __flags; \ > + raw_local_irq_save(__flags); \ > + __ret = raw_cpu_generic_try_cmpxchg_memcmp(pcp, ovalp, nval); \ > + raw_local_irq_restore(__flags); \ > + __ret; \ > +}) > + > +#define this_cpu_generic_cmpxchg_memcmp(pcp, oval, nval) \ > +({ \ > + typeof(pcp) __ret; \ > + unsigned long __flags; \ > + raw_local_irq_save(__flags); \ > + __ret = raw_cpu_generic_cmpxchg_memcmp(pcp, oval, nval); \ > + raw_local_irq_restore(__flags); \ > + __ret; \ > +}) > + > +#define this_cpu_cmpxchg128(pcp, oval, nval) \ > + this_cpu_generic_cmpxchg_memcmp(pcp, oval, nval) > +#define this_cpu_try_cmpxchg128(pcp, ovalp, nval) \ > + this_cpu_generic_try_cmpxchg_memcmp(pcp, ovalp, nval) > + > +#endif /* !__SIZEOF_INT128__ */ > + > +#include <asm-generic/percpu.h> > + > +#endif /* _ASM_PARISC_PERCPU_H */
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