[Qemu-devel] [Bug 1823998] [NEW] qemu-system-aarch64: support kernels bigger than 128MiB

[Mark Rutland]

Public bug reported:

Presently QEMU reserves up to 128MiB of space for an arm64 Linux kernel,
placing the initrd following this, and the dtb following the initrd.

This is not sufficient for some debug configurations of the kernel,
which can be larger than 128MiB. Depending on the relative size of the
kernel Image and unpopulated BSS, the dtb (or kernel) will be clobbered
by the other, resulting in a silent boot failure.

Since v3.17, the kernel Image header exposes a field called image_size,
which describes the entire size of the kernel (including unpopulated
sections such as the BSS) as a 64-bit little-endian value. For kernels
prior to v3.17, this field is zero. This is documented at:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/arm64/booting.txt?h=v5.0#n68

It would be great if QEMU could take the image_size field into account
when placing the initrd and dtb to avoid overlap with the kernel.

** Affects: qemu
     Importance: Undecided
         Status: New


** Tags: feature-request

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https://bugs.launchpad.net/bugs/1823998

Title:
  qemu-system-aarch64: support kernels bigger than 128MiB

Status in QEMU:
  New

Bug description:
  Presently QEMU reserves up to 128MiB of space for an arm64 Linux
  kernel, placing the initrd following this, and the dtb following the
  initrd.

  This is not sufficient for some debug configurations of the kernel,
  which can be larger than 128MiB. Depending on the relative size of the
  kernel Image and unpopulated BSS, the dtb (or kernel) will be
  clobbered by the other, resulting in a silent boot failure.

  Since v3.17, the kernel Image header exposes a field called
  image_size, which describes the entire size of the kernel (including
  unpopulated sections such as the BSS) as a 64-bit little-endian value.
  For kernels prior to v3.17, this field is zero. This is documented at:

  
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/arm64/booting.txt?h=v5.0#n68

  It would be great if QEMU could take the image_size field into account
  when placing the initrd and dtb to avoid overlap with the kernel.

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