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    SubjectRe: [PATCH v4 2/3] arm64: split syscall_trace() into separate functions for enter/exit
    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@linaro.org>
    > ---
    > 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.

    Will


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