[PATCH] ARM: pass syscall return value to sys_exit tracepoint

[Gabbasov, Andrew]

> On Sat, Dec 01, 2012 at 01:38:54PM +0000, Andrew Gabbasov wrote:
> > sys_exit tracepoint expects the syscall return value as a second
> > argument, rather than syscall number.
> >
> > Signed-off-by: Andrew Gabbasov <andrew_gabbasov at mentor.com>
> > ---
> >  arch/arm/kernel/ptrace.c |    2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c
> > index 739db3a..4206da7 100644
> > --- a/arch/arm/kernel/ptrace.c
> > +++ b/arch/arm/kernel/ptrace.c
> > @@ -956,7 +956,7 @@ asmlinkage int syscall_trace_exit(struct pt_regs *regs, int scno)
> >  {
> >       scno = ptrace_syscall_trace(regs, scno, PTRACE_SYSCALL_EXIT);
> >       if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
> > -             trace_sys_exit(regs, scno);
> > +             trace_sys_exit(regs, regs->ARM_r0);
> >       audit_syscall_exit(regs);
> >       return scno;
> >  }
> 
> It might be worth stashing the return value into a local variable prior to
> the ptrace_syscall_trace invocation, just in case a debugger decides to
> rewrite the child's registers.
> 
> Will

The other registers in "regs" structure are not saved around ptrace_syscall_trace,
and both audit_syscall_exit and trace_sys_exit get the register values, potentially
changed by a debugger. Does it make sense to save the isolated return value
for trace_sys_exit call only and not to save other registers, passed, for example,
to audit_syscall_exit function that takes the return value from regs structure?
Isn't it a reasonable assumption that a debugger will preserve important
register values (or intentionally change them for some purpose) in case
of syscall_exit, as we rely on this for syscall_enter case?

Thanks,
Andrew