Re: [PATCH v4 2/3] arm64: split syscall_trace() into separate functions for enter/exit

[AKASHI Takahiro]

On 03/14/2014 03:41 AM, Will Deacon wrote:
> On Thu, Mar 13, 2014 at 10:11:30AM +0000, AKASHI Takahiro wrote:
> > As done in arm, this change makes it easy to confirm we invoke syscall
> > related hooks, including syscall tracepoint, audit and seccomp which would
> > be implemented later, in correct order. That is, undoing operations in the
> > opposite order on exit that they were done on entry.
> >
> > Signed-off-by: AKASHI Takahiro <takahiro.akashi@xxxxxxxxxx>
> > ---
> >   arch/arm64/kernel/entry.S  |   10 ++++-----
> >   arch/arm64/kernel/ptrace.c |   48 ++++++++++++++++++++++++++++++++++----------
> >   2 files changed, 41 insertions(+), 17 deletions(-)
>
> [...]
>
> > diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
> > index 6a8928b..9993a8f 100644
> > --- a/arch/arm64/kernel/ptrace.c
> > +++ b/arch/arm64/kernel/ptrace.c
> > @@ -1058,29 +1058,27 @@ long arch_ptrace(struct task_struct *child, long request,
> >   	return ptrace_request(child, request, addr, data);
> >   }
> >
> > -asmlinkage int syscall_trace(int dir, struct pt_regs *regs)
> > +asmlinkage int syscall_trace_enter(struct pt_regs *regs)
> >   {
> >   	unsigned long saved_reg;
> >
> >   	if (!test_thread_flag(TIF_SYSCALL_TRACE))
> >   		return regs->syscallno;
> >
> > +	/*
> > +	 * A scrach register (ip(r12) on AArch32, x7 on AArch64) is
> > +	 * used to denote syscall entry/exit:
> > +	 *   0 -> entry
> > +	 */
>
> You could add an enum, like we have on ARM (ptrace_syscall_dir) for the two
> directions.
>
> >   	if (is_compat_task()) {
> > -		/* AArch32 uses ip (r12) for scratch */
> >   		saved_reg = regs->regs[12];
> > -		regs->regs[12] = dir;
> > +		regs->regs[12] = 0;
> >   	} else {
> > -		/*
> > -		 * Save X7. X7 is used to denote syscall entry/exit:
> > -		 *   X7 = 0 -> entry, = 1 -> exit
> > -		 */
> >   		saved_reg = regs->regs[7];
> > -		regs->regs[7] = dir;
> > +		regs->regs[7] = 0;
>
> This code could also be refactored so we calculated the register number
> once, then avoid the if (is_compact_task()) check all over the place.
>
> Similarly on the exit path.

OK, I will implement tracehook_report_syscall() as in arm.

-Takahiro AKASHI


> Will
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