set up multiboot information structure

[fabianfreyer]

• if the os image requests it
  • get the upper and lower memory using
    

    bhyve-multiboot/userboot.h

    Lines 186 to 190 in ff5a9bc

    	/*
    	* Return guest physical memory map details
    	*/
    	void (*getmem)(void *arg, uint64_t *lowmem,
    	uint64_t *highmem);

  • set mbi->mem_lower and mbi->mem_upper and set bit 0 of mbi->flags.
  • generate a memory map buffer as described in the multiboot spec, point mbi->mmap_addr to it, set mbi->mmap_length, and set bit 6 of mbi->flags.
• make sure bit 1 of mbi->flags is cleared, as specified:

  If bit 1 in the ‘flags’ word is set, then the ‘boot_device’ field is valid, and indicates which bios disk device the boot loader loaded the OS image from. If the OS image was not loaded from a bios disk, then this field must not be present (bit 3 must be clear).

• if cmdline is given, copy it into the hypervisor, and set mbi->cmdline and set bit 2 of mbi->flags.
• if modules are given, parse their command-line specification and load them:
  • copy them into the guest, page-align them if requested by the kernel.
  • set up an array of module structures, point mbi->mods_addr to it and set mbi->mods_count
• set bit 9 of mbi->flags. copy the bootloader name into the guest and point mbi->boot_loader_name to it.
• if the kernel requests it, set up video modes - although it isn't clear what this means for headless systems.

[fabianfreyer]

For the bhyve memory map, see grub2-bhyve's implementation:

  /*
   * bhyve is going to return the following memory segments
   *
   * 0 - 640K    - usable
   * 640K- 1MB   - vga hole, BIOS, not usable.
   * 1MB - lomem - usable
   * lomem - 4G  - not usable
   * 4G - himem  - usable [optional if himem != 0]
   */
  bhyve_info.nsegs = 2;
  bhyve_info.segs = bhyve_mm;

  bhyve_mm[0].start = 0x0;
  bhyve_mm[0].end = 640*1024;		/* 640K */
  bhyve_mm[0].type = GRUB_MEMORY_AVAILABLE;

  bhyve_mm[1].start = 1024*1024;
  bhyve_mm[1].end = (memsz > lomemsz) ? lomemsz : memsz;
  bhyve_mm[1].type = GRUB_MEMORY_AVAILABLE;

  if (memsz > lomemsz) {
    bhyve_info.nsegs++;
    bhyve_mm[2].start = 4*GB;
    bhyve_mm[2].end = (memsz - lomemsz) + bhyve_mm[2].start;
    bhyve_mm[2].type = GRUB_MEMORY_AVAILABLE;
  }

[fabianfreyer]

Seeing as qemu doesn't support vbe either, I think we can break with the spec here and just error out:

From qemu's hw/i386/multiboot.c:

if (flags & 0x00000004) { /* MULTIBOOT_HEADER_HAS_VBE */
    fprintf(stderr, "qemu: multiboot knows VBE. we don't.\n");
}