Fix building on armv7

[hpux735]

This patch enables compilation from build-script on armv7. I don't expect this patch to be without controversy; rather I'd like this to be the opening point for some discussion about the specific implementation.

In particular, I'd like to draw attention to this PR at foundation: https://github.com/apple/swift-corelibs-foundation/pull/399/files which addresses val_list in the same way as presented here.

Furthermore, PAGE_SIZE is, for some reason, undefined on ARM. The definition provided here is an assumption, and kind of a hack. I'd happy to receive some guidance whether there is a better way to move forward.

Thanks!

[MadCoder]

PAGE_SIZE is in <sys/user.h> on linux I think.

[MadCoder]

yup just checked, it's where it is, don't ask me how I can ever remember things like that...
it should be added to internal.h explicitly, for all platforms this is fine, BSDs have it too

[hpux735]

Very interesting. PAGE_SIZE is not defined in sys/user.h on arm. It's referenced in a few places, but I can't see how it's defined in those cases.

 wdillon@tegra-ubuntu  /usr/include  ack-grep "PAGE_SIZE"
scsi/sg.h
188:#define SG_SCATTER_SZ (8 * 4096)  /* PAGE_SIZE not available to user */
190:   The value must be a power of 2 and <= (PAGE_SIZE * 32) [131072 bytes on
191:   i386]. The minimum value is PAGE_SIZE. If scatter-gather not supported
194:   PAGE_SIZE by calling getpagesize() defined in unistd.h . */

elf.h
1882:#define PF_HP_PAGE_SIZE        0x00100000

arm-linux-gnueabihf/bits/xopen_lim.h
50:   PAGE_SIZE Size of bytes of a page.

arm-linux-gnueabihf/bits/confname.h
135:#define     _SC_PAGE_SIZE           _SC_PAGESIZE

asm-generic/shmparam.h
4:#define SHMLBA PAGE_SIZE       /* attach addr a multiple of this */

linux/resource.h
71:#define MLOCK_LIMIT  ((PAGE_SIZE > 64*1024) ? PAGE_SIZE : 64*1024)

linux/vhost.h
58:#define VHOST_PAGE_SIZE 0x1000

linux/kvm.h
352:    ((PAGE_SIZE - sizeof(struct kvm_coalesced_mmio_ring)) / \
499:#define KVM_PPC_PAGE_SIZES_MAX_SZ   8
509:    struct kvm_ppc_one_page_size enc[KVM_PPC_PAGE_SIZES_MAX_SZ];
512:#define KVM_PPC_PAGE_SIZES_REAL         0x00000001
519:    struct kvm_ppc_one_seg_page_size sps[KVM_PPC_PAGE_SIZES_MAX_SZ];

linux/binfmts.h
14:#define MAX_ARG_STRLEN (PAGE_SIZE * 32)

[MadCoder]

then you should use getpagesize() or sysconf(_SC_PAGESIZE) for the define. I assume arm doesn't define it because there are both 4k and 16k devices out there and it's not tied to the ABI.

[hpux735]

Thanks, @MadCoder !