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** Changed in: qemu
Status: New => Incomplete
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https://bugs.launchpad.net/bugs/1699867
Title:
x86_64 qemu crashes at far call into long-mode
Status in QEMU:
Incomplete
Bug description:
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.
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