On 6 Mar 2018, at 9:28, Rodney W. Grimes wrote:

bios_crtc_base would be part of the isa legacy vga
controller card.  Bhyve does not, at this time, or
in the near future expect to have, support for this
legacy device.


I am wrong on this, the framebuffer device does
infact have support for the legacy i/o addresses
that this should point to.  You should see the
"vgaconf" section of the FrameBuffer section
of the bhyve(8) manpage.

I believe you need to be running bhyve with the
uefi bios options, the with CMS version, and
have vgaconf=on to get your code to work as is.

For diskless multiboot kernels I’m going with a
separate userboot.so-compatible loader. Specifying
a UEFI bootrom implicitly resets the CPU.
(See usr.sbin/bhyve/bhyverun.c:960)

I think deciding to use the serial output (which is
what most of rumpkernel’s cons_init is doing) based
on the hypervisor is probably the right way to go.
Something similar is already done for XEN:

    /*
     * If running under Xen use the serial console.
     */
    if (hypervisor == HYPERVISOR_XEN)
        prefer_serial = 1;

rumprun/platform/hw/arch/x86/cons.c:59:
649 0 350887182668 vm testing[0]: handled exception vmexit at 0x102a56

Therefore, I?m assuming this is the origin of the fault.

Tracking down bios_crtc_base, I find that it?s loaded in
rumprun/platform/hw/arch/amd64/locore.S:70:

        /* save BIOS data area values */
        movw BIOS_COM1_BASE, %bx
        movw %bx, bios_com1_base
        movw BIOS_CRTC_BASE, %bx
        movw %bx, bios_crtc_base

Where BIOS_CRTC_BASE is 0x463 and BIOS_COM1_BASE is 0x400. Checking the bhyve device node in /dev/vmm with xxd(1), I find the words at these addresses to be
Uninitialised:

00000400: 0000                                     ..
00000483: 0000                                     ..
Typo here, should this be 00000463?
Yes, sorry about that.

Fabian

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