Hector Martin

It definitely has a file structure (at least a recent Windows Server 2016 image I'm looking at does). Try 7-zip to extract the ISO, it usually knows how to pull out El Torito images IIRC. For my image the EFI floppy images wind up at efi/microsoft/boot/efisys[_noprompt].bin

Dude see newest tweet, didn't need infodump just needed different machine.

Yeah, sorry, I saw it after the replies. Weird, what tool were you using to extract the contents?

Nautilus, which... Idfk what it was using for a backend. I was being lazy, ths machine I was testing this on was my airgap laptop since it was convenient, but it's horribly out of date too. I copied the windows iso's files and the uefi literally finds it without chainloading.

Yeah, the one nice thing about UEFI is it understands (some) filesystems, so these days you often can just not care about any of the bootloader/bootblock shenanigans and just throw files in there.

Yeah. Ironically, grub can't chainload it correctly because the Windows installer efi appears to try to copy parts of itself into memory by reading directly from the initial boot partition or something??? But it does boot fine if I let the uefi discover it, so I have no clue.

Probably relies on UEFI filesystem access that GRUB does differently. I'm not sure how it integrates with UEFI for these things but I suspect the answer is "not very well" (since GRUB mostly likes using its own drivers/etc).

Yeah, but apparently grub4dos can do it easily by emulating an ISO as a CD or something? Idk, im having a weird time with this one.