[00/18] x86: Improve operation under QEMU

Message

Simon Glass Nov. 12, 2024, 1:58 p.m. UTC

U-Boot can start and boot an OS in both qemu-x86 and qemu-x86_64 but it
is not perfect.

With both builds, executing the VESA ROM causes an intermittent hang, at
least on some AMD CPUs.

With qemu-x86_64 kvm cannot be used since the move to long mode (64-bit)
is done in a way that works on real hardware but not with QEMU. This
means that performance is 4-5x slower than it could be, at least on my
CPU.

We can work around the first problem by using Bochs, which is anyway a
better choice than VESA for QEMU. But this results in the Ubuntu
installer failing to boot via EFI. It isn't clear whether this due to
a problem with the UEFI GOP, or something else. It hangs before the
Ubuntu logo appears.

So this series is unfinished. I thought it best to post what is here in
the hope that others can help work out the kinks.


Simon Glass (18):
  scripts: Add a script for building and booting QEMU
  x86: Expand x86_64 early memory
  RFC: x86: qemu: Switch to bochs display
  x86: qemu: Enable dhrystone
  x86: qemu: Avoid accessing BSS too early
  x86: Drop mpspec from the SPL build
  x86: Add some log categories
  x86: Drop use of CONFIG_REALMODE_DEBUG
  x86: Avoid clearing the VESA display
  x86: Add 64-bit entries to the GDT
  x86: Use defines for the cache flags
  x86: spl: Drop duplicate CPU init
  x86: Drop the message about features missing in 64-bit
  x86: Include stdbool.h in interrupt header
  x86: Tidy up the GDT size in start/16.S
  x86: Disable paging before changing to long mode
  x86: Use the same GDT when jumping to long mode
  x86: Use a simple jump into long mode

 MAINTAINERS                      |   8 ++
 arch/x86/cpu/i386/call64.S       |  35 +++----
 arch/x86/cpu/i386/cpu.c          |  18 +++-
 arch/x86/cpu/qemu/qemu.c         |  20 ++--
 arch/x86/cpu/start.S             |   4 +-
 arch/x86/cpu/start16.S           |   3 +-
 arch/x86/include/asm/interrupt.h |   1 +
 arch/x86/include/asm/processor.h |   5 +-
 arch/x86/lib/Makefile            |   2 +
 arch/x86/lib/bios.c              |  27 +++--
 arch/x86/lib/bios_interrupts.c   |   8 +-
 arch/x86/lib/i8259.c             |   2 +
 arch/x86/lib/spl.c               |   4 +-
 configs/qemu-x86_64_defconfig    |  10 +-
 configs/qemu-x86_defconfig       |   6 +-
 doc/board/emulation/index.rst    |   1 +
 doc/board/emulation/script.rst   |  61 +++++++++++
 scripts/build-qemu.sh            | 175 +++++++++++++++++++++++++++++++
 18 files changed, 331 insertions(+), 59 deletions(-)
 create mode 100644 doc/board/emulation/script.rst
 create mode 100755 scripts/build-qemu.sh