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13

Smallest UTF32 to UTF8 converter

by Bastian Blank — last modified Sep 13, 2008 12:30 PM
Filed Under:

I found some weird opcodes in the s390 instruction set some time ago. I finally want to use it as I have access to such a machine. The result is rather slim:

.globl cu41
        .type   cu41, @function
cu41:
.L2:
        cu41    %r2,%r4
        ipm     %r1
        srl     %r1,28
        chi     %r1,3
        je      .L2
        ltr     %r1,%r1
        je      .L3
        lcr     %r1,%r1
        lgfr    %r3,%r1
.L3:
        lgr     %r2,%r3
        br      %r14

The cu41 opcode translates UTF32 to UTF8. Each "parameter" is a register pair [1], which describes address and length of the buffer. This opcode will return after a not specified number of translated characters. The rest is boiler plate code for condition code checking. The loop makes sure that anything is converted within the function unless another error occured.

[1]An even pair. gcc is not yet able to allocate such pairs on its own, so it is hardcoded.
Comments: 0

PV-GRUB and partitions

by Bastian Blank — last modified Sep 13, 2008 11:35 AM
Filed Under:

Xen 3.3 added a tool called PV-GRUB. It is a GRUB (legacy aka 0.97) built against MiniOS and bootable as a PV kernel. It works fine on a Xen 3.2.1.

It is easy to use, I just set this in my config:

kernel = "/usr/local/lib/xen/boot/pv-grub-x86_64.gz"
extra = "(hd0)/boot/grub/menu.lst"

However it decided to not load my config as defined in the config and simply show me that:

    GNU GRUB  version 0.97  (524288K lower / 0K upper memory)

       [ Minimal BASH-like line editing is supported.   For
         the   first   word,  TAB  lists  possible  command
         completions.  Anywhere else TAB lists the possible
         completions of a device/filename. ]

grubdom>

The reason is quite easy:

grubdom> root (hd0)
 Filesystem type unknown, using whole disk

Some debugging later, the reason is known and fixed.

grubdom> root (hd0)
 Filesystem type is ext2fs, using whole disk

grubdom> kernel /boot/vmlinuz-2.6.27-rc5-amd64

grubdom> initrd /boot/initrd.img-2.6.27-rc5-amd64

grubdom> boot
block error -1 for op 2
close blk: backend at /local/domain/0/backend/vbd/23/51712
[    0.000000] Initializing cgroup subsys cpuset
[    0.000000] Initializing cgroup subsys cpu
[    0.000000] Linux version 2.6.27-rc5-amd64 [...]
[    0.000000] Command line:
[    0.000000] KERNEL supported cpus:
[    0.000000]   Intel GenuineIntel
[    0.000000]   AMD AuthenticAMD
[    0.000000]   Centaur CentaurHauls
[    0.000000] ACPI in unprivileged domain disabled
[...]
[    0.022093] Booting paravirtualized kernel on Xen
[    0.022101] Xen version: 3.2-1
Comments: 0