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SubjectRe: [PATCH v2] selftests/x86: Support Atom for syscall_arg_fault test
On Fri, Mar 8, 2019 at 6:52 AM Tong Bo <bo.tong@intel.com> wrote:
>
> Atom-based CPUs trigger stack fault when invoke 32-bit SYSENTER instruction
> with invalid register values. So we also need SIGBUS handling in this case.
>
> Following is assembly when the fault exception happens.
>
> (gdb) disassemble $eip
> Dump of assembler code for function __kernel_vsyscall:
> 0xf7fd8fe0 <+0>: push %ecx
> 0xf7fd8fe1 <+1>: push %edx
> 0xf7fd8fe2 <+2>: push %ebp
> 0xf7fd8fe3 <+3>: mov %esp,%ebp
> 0xf7fd8fe5 <+5>: sysenter
> 0xf7fd8fe7 <+7>: int $0x80
> => 0xf7fd8fe9 <+9>: pop %ebp
> 0xf7fd8fea <+10>: pop %edx
> 0xf7fd8feb <+11>: pop %ecx
> 0xf7fd8fec <+12>: ret
> End of assembler dump.
>
> According to Intel SDM, this could also be a Stack Segment Fault(#SS, 12),
> except a normal Page Fault(#PF, 14). Especially, in section 6.9 of Vol.3A,
> both stack and page faults are within the 10th(lowest priority) class, and
> as it said, "exceptions within each class are implementation-dependent and
> may vary from processor to processor". It's expected for processors like
> Intel Atom to trigger stack fault(SIGBUS), while we get page fault(SIGSEGV)
> from common Core processors.

Acked-by: Andy Lutomirski <luto@kernel.org>

but:

> - sethandler(SIGSEGV, sigsegv, SA_ONSTACK);
> + sethandler(SIGSEGV, sigsegv_or_sigbus, SA_ONSTACK);
> + /* The actual exception can vary. On Atom CPUs, we get #SS

Can whoever commits this fix the comment formatting? That should be:

/*
* first line here

--Andy

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