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Re: [Xen-devel] Odgovor: Basic bare metal ARM domain interface

On 30/05/16 21:21, Ivan Pavić2 wrote:

Hello Ivan,

Sorry for the late answer.

I used FreeRTOS code for console output. It is based on Mini OS code. There are 
two problems as I've >determined
with debugging. First is that vsnprintf blocks for some reason in print 
function so i commented it out. After the

snprintf blocks...

hypercall function blocked as well. I modified hypercall function so it looks 
like this:
(void)HYPERVISOR_console_io(CONSOLEIO_write, 3, "yes");

As the call failed I decided to make hypervisor call directly in boot procedure, 
so I put this assembler code just >before
branch to main:

        mov r12, #18 ; console io code
        mov r0, #0 ; write operation(first parameter)
        mov r1, #5 ; length of message (second parameter)
       ldr r2, =msg ; message address (third parameter)
        .long 0xe140ea71 ; hvc instruction
        b main ; branch to main

For your information, hypervisor calls have to be done with data cache enabled. Otherwise you not may get garbage (or nothing at all) on the console.

msg is defined as:

    .asciz "hello"

I get deadbeef in registers, apperently something happened (xenctx output):
PC:       4000c5bc
CPSR:     600001f3
USR:               SP:00000000 LR:00000000
SVC: SPSR:00000000 SP:4011c200 LR:400080a8
FIQ: SPSR:00000000 SP:40124200 LR:00000000
IRQ: SPSR:00000000 SP:40120200 LR:00000000
ABT: SPSR:00000000 SP:40128200 LR:00000000
UND: SPSR:00000000 SP:4012c200 LR:00000000

  >r0_usr: 00000000        r1_usr: deadbeef        r2_usr: deadbeef
  >r3_usr: 00000000        r4_usr: 00000000        r5_usr: 00000000
  >r6_usr: 00000000        r7_usr: 00000000        r8_usr: 00000000
  >r9_usr: 00000064       r10_usr: 00000064       r11_usr: 00000000
r12_usr: deadbeef

According to arch-arm.h r0 is return value of call. It is 0, operation 
successful???? Still I don't get output on

Thank you in advance,


Ivan Pavic

I still didn't solve why I don't see no output on emergency console, I think I 
should because if deadbeef in registers it
do_console_io should have been called.

The emergency console and any Xen debug facilities (hvc 0xffxx) only works when the hypervisor has been built with debug enabled.

By default, release version are built with debug disabled. You will have to pass debug=y on the build command line to enable debug.

However new problem emerged i tried to add iomem
parameter in configuration file to get access over gpio but domain won't start 
because operation is not permitted.
Should I somehow release disable that memory space for dom0, perhaps in dts for 

Snippet from dom.cfg file:

iomem = ["0x13400000,1@0x41400000"]

0x13400000 is base address of GPIO that I want to use.

iomem expects a physical page number (see the documentation in docs/man/xl.cfg.pod.5). So it should be:

iomem = ["0x13400,1@0x41400"]

I get this error: (snippet from xl -vvv create -c dom.cfg)

libxl: debug: libxl_create.c:1213:domcreate_launch_dm: dom4 iomem 
libxl: error: libxl_create.c:1220:domcreate_launch_dm: failed give dom4 access 
to iomem range 13400000-13400000: Operation not permitted
libxl: debug: libxl.c:1719:devices_destroy_cb: forked pid 3835 for destroy of 
domain 4

Thank you in advance,


Julien Grall

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