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Date: Wed, 1 Nov 2017 13:32:50 -0700 From: Mark Salyzyn <salyzyn@...roid.com> To: Mark Rutland <mark.rutland@....com> Cc: Robin Murphy <robin.murphy@....com>, linux-kernel@...r.kernel.org, Christoffer Dall <cdall@...aro.org>, Stefan Traby <stefan@...lo-penguin.com>, Suzuki K Poulose <suzuki.poulose@....com>, Marc Zyngier <marc.zyngier@....com>, Catalin Marinas <catalin.marinas@....com>, Will Deacon <will.deacon@....com>, Dave Martin <Dave.Martin@....com>, linux-arm-kernel@...ts.infradead.org Subject: Re: [PATCH] arm64: write_sysreg asm illegal for aarch32 On 11/01/2017 11:16 AM, Mark Salyzyn wrote: > On 11/01/2017 10:56 AM, Mark Rutland wrote: >> On Wed, Nov 01, 2017 at 10:49:00AM -0700, Mark Salyzyn wrote: >>> On 11/01/2017 10:14 AM, Robin Murphy wrote: >>>> On 01/11/17 16:58, Mark Salyzyn wrote: >>>>> Cross compiling to aarch32 (for vdso32) using clang correctly >>>>> identifies that (the unused) write_sysreg inline asm directive is >>>>> illegal in that architectural context: >>>>> >>>>> arch/arm64/include/asm/arch_timer.h: error: invalid input >>>>> constraint 'rZ' in asm >>>>> write_sysreg(cntkctl, cntkctl_el1); >>>>> ^ >>>>> arch/arm64/include/asm/sysreg.h: note: expanded from macro >>>>> 'write_sysreg' >>>>> : : "rZ" (__val)); >>>>> ^ >>>>> >>>>> GCC normally checks for correctness everywhere. But uniquely for >>>>> unused asm, will optimize out and suppress the error report. >>>> It sounds more like some paths are wrong in the compat vDSO build if >>>> it's pulling in this header in the first place - nothing in this >>>> file is >>>> relevant to AArch32. >>>> >>>> Robin. >>>> >>> And yet, when you CROSS_COMPILE_ARM32 a vdso32, you have no choice >>> but to >>> utilize the arm64 headers since they contain all the relevant kernel >>> structures and environment. >> This itself is the underlying issue. >> >> When building the compat VDSO, we must ensure that we only include >> headers that make sense for 32-bit arm. >> >> If the build system can't do that today, we should rework it so that it >> can. Anything else cannot be a complete fix. >> >>> asm/arch_timer.h (remember we are using arm instructions to access >>> arch64 >>> timers) >>> >>> linux/time.h (really only for struct timespec()) >>> >>> asm/processor.h (eg: cpu_relax()) >>> >>> pull in a _lot_ of architectural related cruft that always somehow >>> picks up >>> asm/sysreg.h somewhere in the multitude of includes to fulfill some >>> unused >>> inline's needs. >> ... these are just the particular symptoms this problem results in >> today. >> >> Thanks, >> Mark. > > Ok, will attack it and see just how bad the scale is... > > . . . > > -- Mark > > Scoped, not as bad as I thought, but there is some open-coded evilness to fix: 1) linux/jiffies.h can not be included, replace with open coding: #include <asm/param.h> #define TICK_NSEC TICK_NSEC ((NSEC_PER_SEC+HZ/2)/HZ) 2) linux/hrtimer.h can not be included, replace with open coding (must have above to work): #define LOW_RES_NSEC TICK_NSEC #ifdef CONFIG_HIGH_RES_TIMERS # define HIGH_RES_NSEC 1 # define MONOTONIC_RES_NSEC HIGH_RES_NSEC #else # define MONOTONIC_RES_NSEC LOW_RES_NSEC #endif 3) asm/processor.h can not be included, replace with open coding: static inline void cpu_relax(void) { asm volatile("yield" ::: "memory"); } 4) linux/time.h can not be included, replace with open coding: #include <linux/compiler.h> #include <linux/math64.h> #include <uapi/linux/time.h> #define NSEC_PER_SEC 1000000000L static __always_inline void timespec_add_ns(struct timespec *a, u64 ns) { a->tv_sec += __iter_div_u64_rem(a->tv_nsec + ns, NSEC_PER_SEC, &ns); a->tv_nsec = ns; } I am at a loss to determine if there is an acceptable way to split off the open-coding. For instance asm-generic/processor.h (for cpu_relax()), uapi/linux/hrtimer.h and uapi/linux/jiffies.h for the #defines (uapi is a bad choice, flipping coin?). The time open-coding is probably OK given that they have not changed since near the limits of git history. -- Mark
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