[Bug 1916112] Re: Illegal instruction crash of QEMU on Jetson Nano

[Stefan Weil]

TCG works and I get a Linux boot prompt in the guest Raspbian when
vector instructions for TCG are disabled, so obviously the undefined
instruction is simply unsupported for Jetson Nano and Xavier.

Patch used to disable it:

diff --git a/tcg/aarch64/tcg-target.h b/tcg/aarch64/tcg-target.h
index 5ec30dba25..2240adad1e 100644
--- a/tcg/aarch64/tcg-target.h
+++ b/tcg/aarch64/tcg-target.h
@@ -125,8 +125,8 @@ typedef enum {
 #define TCG_TARGET_HAS_mulsh_i64        1
 #define TCG_TARGET_HAS_direct_jump      1
 
-#define TCG_TARGET_HAS_v64              1
-#define TCG_TARGET_HAS_v128             1
+#define TCG_TARGET_HAS_v64              0
+#define TCG_TARGET_HAS_v128             0
 #define TCG_TARGET_HAS_v256             0
 
 #define TCG_TARGET_HAS_andc_vec         1

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https://bugs.launchpad.net/bugs/1916112

Title:
  Illegal instruction crash of QEMU on Jetson Nano

Status in QEMU:
  Confirmed

Bug description:
  I have a jetson nano (arm64 SBC) and I want to check the native
  emulation performance of Raspbian Buster. I used the info available
  here:

  https://github.com/dhruvvyas90/qemu-rpi-kernel/tree/master/native-
  emuation

  I have Xubuntut 20.04 with KVM enabled kernel running on the Jetson
  Nano

  However QEMU crashes with "Illegal Instruction" during kernel boot. I
  have a built latest QEMU from sources with following configuration

  ./configure --prefix=/usr/local --target-list=aarch64-softmmu,arm-
  softmmu  --enable-guest-agent --enable-vnc  --enable-vnc-jpeg
  --enable-vnc-png --enable-kvm --enable-spice --enable-sdl --enable-gtk
  --enable-virglrenderer --enable-opengl

  qemu-system-aarch64 --version
  QEMU emulator version 5.2.50 (v5.2.0-1731-g5b19cb63d9)

  When I run as follows:

  ../build/qemu-system-aarch64 -M raspi3
  -append "rw earlyprintk loglevel=8 console=ttyAMA0,115200 
dwc_otg.lpm_enable=0 root=/dev/mmcblk0p2 rootdelay=1"
  -dtb ./bcm2710-rpi-3-b-plus.dtb
  -sd 
/media/96747D21747D0571/JetsonNano/2020-08-20-raspios-buster-armhf-full.qcow2
  -kernel ./kernel8.img
  -m 1G -smp 4 -serial stdio -usb -device usb-mouse -device usb-kbd

  I get :
  [ 74.994834] systemd[1]: Condition check resulted in FUSE Control File System 
being skipped.
  [ 76.281274] systemd[1]: Starting Apply Kernel Variables...
  Starting Apply Kernel Variables...
  Illegal instruction (core dumped)

  When I use GDB I see this:

  Thread 8 "qemu-system-aar" received signal SIGILL, Illegal instruction.
  [Switching to Thread 0x7fad7f9ba0 (LWP 28037)]
  0x0000007f888ac690 in code_gen_buffer ()
  (gdb) bt
  #0 0x0000007f888ac690 in code_gen_buffer ()
  #1 0x0000005555d7c038 in cpu_tb_exec (tb_exit=, itb=, cpu=0x7fb4502c40)
  at ../accel/tcg/cpu-exec.c:191
  #2 cpu_loop_exec_tb (tb_exit=, last_tb=, tb=, cpu=0x7fb4502c40)
  at ../accel/tcg/cpu-exec.c:708
  #3 cpu_exec (cpu=cpu@entry=0x7fb4502c40) at ../accel/tcg/cpu-exec.c:819
  ..

  I have just two questions:

  Is this a problem with QEMU or is there anything specific build or
  options I need to use. Any specific version of QEMU should be used ?

  Why is TCG used as the accelerator when KVM is present. Is it possible
  and how to use KVM ?

  If I enabled the KVM then I get this error:

  ../build/qemu-system-aarch64 -M raspi3 -enable-kvm -append "rw earlyprintk 
loglevel=8 console=ttyAMA0,115200 dwc_otg.lpm_enable=0 root=/dev/mmcblk0p2 
rootdelay=1" -dtb ./bcm2710-rpi-3-b-plus.dtb -sd 
/media/96747D21747D0571/JetsonNano/2020-08-20-raspios-buster-armhf-full.qcow2 
-kernel ./kernel8.img -m 1G -smp 4 -serial stdio -usb -device usb-mouse -device 
usb-kbd
  WARNING: Image format was not specified for 
'/media/96747D21747D0571/JetsonNano/2020-08-20-raspios-buster-armhf-full.img' 
and probing guessed raw.
           Automatically detecting the format is dangerous for raw images, 
write operations on block 0 will be restricted.
           Specify the 'raw' format explicitly to remove the restrictions.
  qemu-system-aarch64: ../softmmu/physmem.c:750: cpu_address_space_init: 
Assertion `asidx == 0 || !kvm_enabled()' failed.

  Thanks a lot.

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