From mboxrd@z Thu Jan 1 00:00:00 1970 From: catalin.marinas@arm.com (Catalin Marinas) Date: Tue, 15 Oct 2013 18:46:29 +0100 Subject: [RFC v3 PATCH 1/7] ARM: add support for kernel mode NEON in atomic context In-Reply-To: References: <1381666503-23726-1-git-send-email-ard.biesheuvel@linaro.org> <1381666503-23726-2-git-send-email-ard.biesheuvel@linaro.org> <20131015172604.GA4765@arm.com> Message-ID: <20131015174629.GC4765@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Tue, Oct 15, 2013 at 06:30:50PM +0100, Ard Biesheuvel wrote: > On 15 October 2013 19:26, Catalin Marinas wrote: > > On Sun, Oct 13, 2013 at 01:14:57PM +0100, Ard Biesheuvel wrote: > >> diff --git a/arch/arm/include/asm/neon.h b/arch/arm/include/asm/neon.h > >> index 8f730fe..800d85c 100644 > >> --- a/arch/arm/include/asm/neon.h > >> +++ b/arch/arm/include/asm/neon.h > >> @@ -8,10 +8,30 @@ > >> * published by the Free Software Foundation. > >> */ > >> > >> +#include > >> +#include > >> +#include > >> #include > >> > >> #define cpu_has_neon() (!!(elf_hwcap & HWCAP_NEON)) > >> > >> +/* > >> + * Avoid wasting stack space by making the size of the allocated area depend on > >> + * whether we are currently running in process context. (If this is the case, we > >> + * will use the normal preserve/restore mechanism, leaving the allocated stack > >> + * space unused.) > >> + */ > >> +#define __QREG_SIZE(num) \ > >> + ((!in_interrupt()) ? 0 : (num) > 16 ? 256 : 16 * (((num) + 1) & ~1U)) > >> + > >> +#define DEFINE_NEON_REGSTACK_PARTIAL(v, num) \ > >> + struct { \ > >> + struct vfp_partial_state regs; \ > >> + u8 qregs[__QREG_SIZE(num)]; \ > >> + } v > > > > Oh, interesting gcc feature. What does it generate? > > > > Well, it's not a feature particular to GCC, as far as I am aware. The > anonymous struct is just runtime variably sized depending on > in_interrupt() and the requested number of registers. OK, it looks like it's valid C99. I was worried the compiler may generate something like an alloca() library call. -- Catalin