Re: [PATCH] arm64: write_sysreg asm illegal for aarch32

[Mark Salyzyn]

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