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Date: Wed, 1 Nov 2017 10:49:00 -0700 From: Mark Salyzyn <salyzyn@...roid.com> To: Robin Murphy <robin.murphy@....com>, linux-kernel@...r.kernel.org Cc: Mark Rutland <mark.rutland@....com>, 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 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. 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. -- Mark
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