Re: [Xen-devel] [PATCH, updated] i386 linux: eliminate hard coded items from __xen_guest section

["Christian Limpach" <christian.limpach@xxxxxxxxx>]

On 2/17/06, Jan Beulich <JBeulich@xxxxxxxxxx> wrote:
> To allow the new VMSPLIT_* Kconfig options to work, and to avoid problems 
> when the position of the hypercall page
> changes, this patch eliminates the hard-coded entries in the __xen_guest 
> section in head.S.
> Unfortunately the original version didn't work with gas newer than beginning 
> of August 2005, where in an attempt to fix
> another problem a regression was introduced.

The calculation doesn't seem to work on 32-bit for PAGE_OFFSET >=
2^31, at least not with:
cl349@firebug:~/ls/xen-unstable-clean.hg$ as --version
GNU assembler 2.15.92.0.2 20040927

I'll checkin the following:
.macro bigutoa value
    utoa (\value) >> 12
    .ascii "000"
.endm
.macro utoa value
 .if (\value) >= 16
        utoa (\value) >> 4
 .endif
 .if (\value) % 16 < 10
  .byte '0' + (\value) % 16
 .else
  .byte 'A' + (\value) % 16 - 10
 .endif
.endm

.section __xen_guest
        .ascii  "GUEST_OS=linux,GUEST_VER=2.6"
        .ascii  ",XEN_VER=xen-3.0"
        .ascii  ",VIRT_BASE=0x"; bigutoa __PAGE_OFFSET
        .ascii  ",HYPERCALL_PAGE=0x"; utoa
((__PHYSICAL_START+HYPERCALL_PAGE_OFFSET)>>PAGE_SHIFT)

It's a bit gross, maybe there's a neater solution.

     christian

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