[PATCH 53-55] (Was: Q: what user_enable_single_step() actually means?)

[Roland McGrath]

> > it being after the syscall insn, but (in vanilla ptrace, and at the
> > time of report_clone callbacks at utrace level) without the return
> > value register having been written yet.
> 
> And how we can implement this?
> 
> regs->ax is updated right after "call *sys_call_table[]", and we
> report PTRACE_EVENT_FORK or PTRACE_EVENT_EXEC much later.

I didn't intend to.  This is a change I think is more desireable than the
bug-compatibility.  In today's ptrace these extra stops are the sole
exceptions where the register state you fiddle with ptrace gets clobbered
later.  I've never thought that was useful.

> The current logic which delays the stop adds so many complications...

Of course, everything is open for debate.  IMHO it is the old ptrace ABI's
totally wrong model that introduces complexity.  We don't want that same
wrongness in the utrace API model.  It's only the legacy ptrace behavior
that necessitates these hacks.


Thanks,
Roland