baremetal-helloworld: Enable x86 and x86-64 ports

- The qemux86 port for helloworld-baremetal builds in the standard way, however,
  it uses NASM syntax for the startup code, hence we include a dependency to
  nasm-native, QEMU forces us to use an ELF file rather than a bin file to boot
  from this architecture using the -kernel parameter.

- QEMU refuses to boot using the -kernel parameter for files containing an ELF64
  header [1], instead, it requires a multiboot2 compatible image.

  We could create an image that contains a multiboot2 header by piggybacking
  into grub2-native, specifically grub-mkrescue, but it requires some extra
  runtime dependencies (xorriso which is currently part of meta-oe), and assumes
  a grub installation exists on the host.

  Due to host contamination and dependency complications, we dont rely on grub2,
  but rather do this process manually instead, the x86-64 port contains a stage1
  bootloader, stage2 bootloader and a 64 bit baremetal app (multiboot2
  compatible), booting into real (16 bit), protected (32 bit) and long (64 bit)
  modes, eventually running the helloworld-baremetal app. This is the reason why
  we need the code changes to use a separate Makefile, and create an image
  specifically for qemux86-64.

$ runqemu nographic
Booting from ROM..
Hello OpenEmbedded on x86!

$ runqemu nographic
Starting Stage 1 Bootloader
Loading Stage 2 Bootloader
Stage 2 Loaded.
Jumping to Stage2 Bootloader
In Stage 2
Done

Hello OpenEmbedded on x86-64!

[1] https://gitlab.com/qemu-project/qemu/-/blob/v7.2.0/hw/i386/multiboot.c#L199

(From OE-Core rev: 1dffd81b2991f90ab95cb36d8ff7626efd21434f)

Signed-off-by: Alejandro Enedino Hernandez Samaniego <alejandro@enedino.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

1 files changed, 5 insertions, 0 deletions

diff --git a/meta/classes-recipe/baremetal-image.bbclass b/meta/classes-recipe/baremetal-image.bbclass
index 513155e9ae..70791f999a 100644
--- a/meta/classes-recipe/baremetal-image.bbclass
+++ b/meta/classes-recipe/baremetal-image.bbclass
@@ -86,6 +86,11 @@ QB_DEFAULT_FSTYPE ?= "bin"
 QB_DTB ?= ""
 QB_OPT_APPEND:append = " -nographic"
 
+# QEMU x86 requires an .elf kernel to boot rather than a .bin
+QB_DEFAULT_KERNEL:qemux86 ?= "${IMAGE_LINK_NAME}.elf"
+# QEMU x86-64 refuses to boot from -kernel, needs a multiboot compatible image
+QB_DEFAULT_FSTYPE:qemux86-64 ?= "iso"
+
 # RISC-V tunes set the BIOS, unset, and instruct QEMU to
 # ignore the BIOS and boot from -kernel
 QB_DEFAULT_BIOS:qemuriscv64 = ""