On 23.01.2023 19:30, Erdem Aktas wrote:
On Fri, Jan 20, 2023 at 4:28 PM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
On Sat, Jan 21, 2023, Ackerley Tng wrote:
Some SSE instructions assume a 16-byte aligned stack, and GCC compiles
assuming the stack is aligned:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=40838. This combination
results in a #GP in guests.
Adding this compiler flag will generate an alternate prologue and
epilogue to realign the runtime stack, which makes selftest code
slower and bigger, but this is okay since we do not need selftest code
to be extremely performant.
Huh, I had completely forgotten that this is why SSE is problematic. I ran into
this with the base UPM selftests and just disabled SSE. /facepalm.
We should figure out exactly what is causing a misaligned stack. As you've noted,
the x86-64 ABI requires a 16-byte aligned RSP. Unless I'm misreading vm_arch_vcpu_add(),
the starting stack should be page aligned, which means something is causing the
stack to become unaligned at runtime. I'd rather hunt down that something than
paper over it by having the compiler force realignment.
Is not it due to the 32bit execution part of the guest code at boot
time. Any push/pop of 32bit registers might make it a 16-byte
unaligned stack.
32-bit stack needs to be 16-byte aligned, too (at function call boundaries) -
see [1] chapter 2.2.2 "The Stack Frame"
Thanks,
Maciej
[1]: https://www.uclibc.org/docs/psABI-i386.pdf
