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assembler/qemu: extract grub2 boot image writing

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Extract the small piece of code that writes the grub2's boot image,
i.e. the first stage of the bootloader that will in turn jump to
the second stage. Currently the position of the core is hard-coded
to be the MBR gap, i.e. the gap between the MBR and the start of
the first partition. This is not a necessity, e.g. when using a
dedicated BIOS boot partition on GPT partition layouts. This re-
factoring should make it easier to add code dealing with such
situations.
This commit is contained in:
Christian Kellner 2020-01-03 12:01:33 +01:00 • committed by Lars Karlitski
parent b9b2f99123
commit c83019a264
1 changed files with 12 additions and 5 deletions
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17
assemblers/org.osbuild.qemu
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@ -350,6 +350,17 @@ def partition_table_from_options(options) -> PartitionTable:
return PartitionTable(pttype, ptuuid, parts)
def grub2_write_boot_image(boot_f: BinaryIO,
image_f: BinaryIO):
"""Write the boot image (grub2 stage 1) to the MBR"""
# The boot.img file is 512 bytes, but we must only copy the first 440
# bytes, as these contain the bootstrapping code. The rest of the
# first sector contains the partition table, and must not be
# overwritten.
image_f.write(boot_f.read(440))
def grub2_write_core_mbrgap(core_f: BinaryIO,
image_f: BinaryIO,
pt: PartitionTable):
@ -445,11 +456,7 @@ def install_grub2(image: str, pt: PartitionTable, options):
# The purpose of this is simply to jump into the stage-2 bootloader.
# On ppc64le & Open Firmware stage-2 is loaded by the firmware
with open(boot_path, "rb") as boot_f:
# The boot.img file is 512 bytes, but we must only copy the first 440
# bytes, as these contain the bootstrapping code. The rest of the
# first sector contains the partition table, and must not be
# overwritten.
image_f.write(boot_f.read(440))
grub2_write_boot_image(boot_f, image_f)
with open(core_path, "rb") as core_f:
if platform == "powerpc-ieee1275":