[Xen-devel] Re: softirq change was Re: domu_debug support removed on march 25th from traps.c in -unstable

[Kip Macy <kip.macy@xxxxxxxxx>]

> You mean that the TF bit is not cleared by the domu_debug code when it
> should be? The correct place to fix this is in
> include/asm-x86/debugger.h in debugger_trap_entry().

Yes. Continuing after single-stepping no longer works.

> In general (not using domu_debug) it is not Xen's job to clear TF. We
> clear it when we 'bounce' the exception into the guest OS, but the
> saved application stack frame will include EFLAGS with the TF bit still
> set. This matches real hardware.

No it isn't Xen's job to clear it under normal circumstances as that
would break PTRACE_SINGLESTEP in user-space. However, it was what the
PDB code was doing and it seemed easy enough to clear it there to
emulate PTRACE_SINGLESTEP for the kernel.

I honestly don't care where it happens, it is easy enough to clear the
TF from xc_ptrace.c. I just happened to be *extremely* tired last
night and was dealing with other issues, so I was frustrated when that
didn't work. I'll just incorporate my fix to xc_ptrace.c in with the
FreeBSD fixes for -unstable.


             -Kip

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