debug: 0.233
boot: 0.146
other: 0.112
graphic: 0.079
semantic: 0.078
device: 0.077
performance: 0.045
PID: 0.045
socket: 0.044
files: 0.041
KVM: 0.032
network: 0.025
permissions: 0.024
vnc: 0.020
debug: 0.627
boot: 0.240
files: 0.041
other: 0.018
PID: 0.015
semantic: 0.015
performance: 0.008
device: 0.006
network: 0.006
graphic: 0.006
vnc: 0.005
socket: 0.005
KVM: 0.004
permissions: 0.003

x86_64 qemu crashes at far call into long-mode

I am experimenting with this OS https://github.com/phil-opp/blog_os and spotted a weird behavior with qemu.

I am looking at code that does transition from 32bit mode to 64bit mode. Right now it does 'jmp $SELECTOR,64bitfunction'. https://github.com/phil-opp/blog_os/blob/557c6a58ea11e31685b9d014d307002d64df5c22/src/arch/x86_64/boot.asm#L32

This code works fine with qemu/kvm/vmware.

To transition from 32 to 64 bit code it is possible to use 'call' operation. So I am trying to replace that code with 'call $SELECTOR,64bitfunction'. It works fine with kvm and wmware. But it fails with Qemu emulation. See the interrup debug log attached. qemu crashes at 10302c (far call mnemonic).


  103016:       e8 18 00 00 00          callq  103033 <set_up_page_tables>
  10301b:       e8 5c 00 00 00          callq  10307c <enable_paging>
  103020:       e8 ec 00 00 00          callq  103111 <set_up_SSE>
  103025:       0f 01 15 28 00 10 00    lgdt   0x100028(%rip)        # 203054 <GCC_except_table2+0xdb5f8>
  10302c:       9a                      (bad)  
  10302d:       40 31 10                rex xor %edx,(%rax)
  103030:       00 08                   add    %cl,(%rax)


As the code works at hardware I expect it to work with qemu. Thus current qemu behavior looks like a bug.



The QEMU project is currently considering to move its bug tracking to another system. For this we need to know which bugs are still valid and which could be closed already. Thus we are setting older bugs to "Incomplete" now.
If you still think this bug report here is valid, then please switch the state back to "New" within the next 60 days, otherwise this report will be marked as "Expired". Or mark it as "Fix Released" if the problem has been solved with a newer version of QEMU already. Thank you and sorry for the inconvenience.

[Expired for QEMU because there has been no activity for 60 days.]