Steps to reproduce:

1. Grab a copy of iPXE
2. Compile it according to the instructions here. Don't forget to change the iPXE script (you may also want to download the Prekernel binary and boot it instead of the Kernel, the document is a bit outdated now).
3. Use qemu-system-i386 to boot it like so:

qemu-system-i386 -hda bin/ipxe.usb -m 4096

iPXE should boot and start to fetch the components over the network.

The problem:

[init_stage2(1:1)]: VirtualRangeAllocator: Failed to allocate anywhere: size=825114624, alignment=4096
[init_stage2(1:1)]: RamdiskController: Failed to allocate kernel region of size 825114624
[init_stage2(1:1)]: KERNEL PANIC! :^(
[init_stage2(1:1)]: StorageManagement: boot device hd0 not found
[init_stage2(1:1)]: at ./Kernel/Storage/StorageManagement.cpp:141 in void Kernel::StorageManagement::determine_boot_device()
[init_stage2(1:1)]: Kernel + 0x00498dad  Kernel::__panic(char const*, unsigned int, char const*) +0x11c
[init_stage2(1:1)]: Kernel + 0x00761b22  Kernel::StorageManagement::determine_boot_device() [clone .localalias] +0x38e
[init_stage2(1:1)]: Kernel + 0x00765325  Kernel::StorageManagement::initialize(AK::String, bool) +0xf7
[init_stage2(1:1)]: Kernel + 0x00658824  Kernel::init_stage2(void*) +0x1289
[init_stage2(1:1)]: Kernel + 0x0066b9cc  exit_kernel_thread +0x0

Suggestion how to fix:

1. Create a stripped version of the disk image, so the Kernel won't have to allocate almost 800 MiB of memory for the ramdisk.
2. Try to utilize x86_64 physical address space to copy the contents of the ramdisk above the 4 GiB boundary (this is ofc valid only for x86_64 platforms).