[PATCH v7 7/9] ARM: add vdso user-space code

[Russell King - ARM Linux]

On Sun, Jun 29, 2014 at 10:48:13AM -0500, Nathan Lynch wrote:
> On 06/29/2014 03:34 AM, Russell King - ARM Linux wrote:
> > On Sat, Jun 28, 2014 at 04:35:12PM -0500, Nathan Lynch wrote:
> >> That's consistent with my results on iMX6.  The reported 1.00x "speedup"
> >> for clock-gettime-monotonic etc indicates the VDSO is falling back to
> >> syscall.
> >>
> >> Thanks for testing.
> > 
> > Here's another issue which cropped up when I ran this patch set through
> > the autobuilder last night - allnoconfig's now fail with:
> > 
> > mm/memory.c: In function 'gate_vma_init':
> > mm/memory.c:3410:22: error: 'FIXADDR_USER_START' undeclared (first use in this function)
> > mm/memory.c:3411:20: error: 'FIXADDR_USER_END' undeclared (first use in this function)
> > mm/memory.c: In function 'in_gate_area_no_mm':
> > mm/memory.c:3432:15: error: 'FIXADDR_USER_START' undeclared (first use in this function)
> > mm/memory.c:3432:46: error: 'FIXADDR_USER_END' undeclared (first use in this function)
> > make[2]: *** [mm/memory.o] Error 1
> 
> arch/arm/include/page.h:
> #ifdef CONFIG_KUSER_HELPERS
> #define __HAVE_ARCH_GATE_AREA 1
> #endif
> 
> mm/memory.c:
> #if !defined(__HAVE_ARCH_GATE_AREA)
> 
> #if defined(AT_SYSINFO_EHDR)
> static struct vm_area_struct gate_vma;
> 
> static int __init gate_vma_init(void)
> {
> 	gate_vma.vm_mm = NULL;
> 	gate_vma.vm_start = FIXADDR_USER_START;
> 	gate_vma.vm_end = FIXADDR_USER_END;
> ...
> 
> The vdso patches add an ARM definition for AT_SYSINFO_EHDR.  So when
> CONFIG_KUSER_HELPERS=n, this code is pulled in now...
> 
> Not sure what the fix would be right now.  I don't understand why there
> is this relationship between AT_SYSINFO_EHDR and gate vma code.

Me neither.  It looks like changing those tests for AT_SYSINFO_EHDR to
something like __HAVE_GATE_VMA or CONFIG_HAVE_GATE_VMA would be a good
step, so we can keep this disabled on ARM.  I don't see a need for the
gate VMA stuff just because we have a vDSO.

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