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

[Elouan Appéré]

Sure.

* For both: extract the archive in the same folder, chmod to it & run

qemu-system-aarch64 -nographic -machine virt,secure=on,virtualization=on
,gic-version=2 -cpu cortex-a57 -smp 2 -m 1024 -bios bl1.bin -d unimp
-semihosting-config enable,target=native -serial mon:stdio -s -S

* In another terminal window, same folder:

aarch64-none-elf-gdb thermosphere.elf

* while in GDB:

target remote :1234

This .elf corresponds to bl33.bin which runs in EL2 (the other binary
files are Arm Trusted Firmware).

===================

For
https://bugs.launchpad.net/qemu/+bug/1838277/+attachment/5279996/+files/example.zip:

* in GDB:

b *0x6000010C

* GDB should report it placed a breakpoint in main.c, line 11 (this is
on a brk instruction). Then:

continue
disas

* Here you should see => 0x000000006000010c <+36>:    brk     #0x3e8

* Notice VBAR_EL2 has a valid, non-zero value:

p $VBAR_EL2

* gdb reports: $1 = 0x60001000

* Step the instruction, the control-C:

stepi

__Expected behavior__: qemu should have jumped to 0x60001000+0x200
__Actual behavior__: qemu jumps to 0+0x200


====================

Erratum: there was an issue in example #2, which was a bug on my part.
Above regression still stands

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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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