[Qemu-devel] [Bug 1838277] Re: qemu-system-aarch64: regression: TCG sometimes using wrong values for VBAR_EL2 despite it being correctly reported to GDB

[Peter Maydell]

This bug is specific to our handling of the 'brk' insn (and other debug
exceptions within the guest like singlestep or watchpoints or
breakpoints) at EL2, so you can work around it for the moment by
avoiding using hardcoded brk insns in your EL2 code.

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https://bugs.launchpad.net/bugs/1838277

Title:
  qemu-system-aarch64: regression: TCG sometimes using wrong values for
  VBAR_EL2 despite it being correctly reported to GDB

Status in QEMU:
  New

Bug description:
  Affects 3.1.0 (latest stable release) and latest commit
  (893dc8300c80e3dc32f31e968cf7aa0904da50c3) but did *not* affect 2.11
  (qemu from bionic ubuntu LTS).

  With the following code and shell commands:

  test.s:

  .text
  mov x0, #0x60000000
  msr vbar_el2, x0
  dsb sy
  isb sy

  $ aarch64-none-elf-as test.s -o test.o
  $ aarch64-none-elf-objcopy -S -O binary test.o test.bin
  $ qemu-system-aarch64 -nographic -machine virt,virtualization=on -cpu 
cortex-a57 -kernel test.bin -s -S

  vbar_el2 is still 0 after the code, instead of being the expected
  0x60000000. (see screenshot).

  This regression doesn't seem to happen for vbar_el1 &
  virtualization=off.

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