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SubjectRe: Compat 32-bit syscall entry from 64-bit task!?
Date
On Thursday 26 January 2012 01:59, Jamie Lokier wrote:
> Denys Vlasenko wrote:
> > (2) syscall exit compat-ness is known from entry type - no need to indicate it; and
> > (3) if we would flag syscall entry with an event value in wait status, then syscall
> > exit will be already distinquisable.
> >
> > Thus, minimally we need one new option, PTRACE_O_TRACE_SYSENTRY -
> > "on syscall entry ptrace stop, set a nonzero event value in wait status"
> > , and two event values: PTRACE_EVENT_SYSCALL_ENTRY (for native entry),
> > PTRACE_EVENT_SYSCALL_ENTRY1 for compat one.
>
> PTRACE_EVENT_SYSCALL_EXIT would cleanly indicate that the new option
> is actually working without the tracer needing to do a fork+test, if
> PTRACE_ATTACH is used and for some reason the tracer sees a syscall
> exit first.

Can't happen. After PTRACE_ATTACH, you can only see tracee dying, or
getting a signal delivery (usually a SIGSTOP). Anything else
would be a kernel bug.

--
vda


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