Re: strace 4.15 released

[Dmitry V. L. <ld...@al...>]

Hi,

On Tue, Jan 03, 2017 at 06:02:44PM +0000, James Cowgill wrote:
> On 20/12/16 00:36, Steve McIntyre wrote:
> > On Tue, Dec 20, 2016 at 03:16:17AM +0300, Dmitry V. Levin wrote:
> >> On Tue, Dec 20, 2016 at 12:50:29AM +0100, Nahim El Atmani wrote:
> >>> On Mon, 19 Dec 2016 18:30:29 +0000, Steve McIntyre wrote:
> >>>> I'm seeing test suite failures on mips[1], mipsel[2] and mips64el[3]
> >>>> on Debian machines.
> >>>>
> >>>> The 32-bit builds are both showing issues with fault injection. I
> >>>> can't follow what the code is meant to be doing here, so no
> >>>> ideas on what's wrong. :-(
> >>>
> >>> As Dmitry said earlier:
> >>>
> >>> On Tue, 15 Nov 2016 15:43:59 +0300, Dmitry V. Levin wrote:
> >>>> Well, the mips kernel does not implement substitution of syscall numbers
> >>>
> >>> So it looks like the test has failed to SKIP on this target.
> >>
> >> As I'm not 100% sure there is no kernel support for mips, I decided
> >> not to skip the test on mips until somebody investigates.
> > 
> > Ah, OK. James Cowgill is my friendly local mips expert - let's see
> > what he thinks... :-)
> 
> I've had a look and I think there is a kernel bug here - specifically
> affecting 32-bit programs run on 64-bit kernels (like all the Debian
> buildds and the porterbox are). An extra PTRACE_SYSCALL stop is
> happening which confuses everything. I'll look some more tomorrow.

Indeed, it seems to be a kernel bug in scall64-o32.S and scall64-n32.S.

According to current arch/mips/kernel/scall64-o32.S:trace_a_syscall
(the same applies to arch/mips/kernel/scall64-n32.S),

if the syscall number after the first syscall_trace_enter call is out
of range, there is a jump to not_o32_scall which in turn jumps to
arch/mips/kernel/scall64-64.S:handle_sys64 (or to handle_sysn32 which
then jumps on to handle_sys64).

Handle_sys64, unsurprisingly, does all over again, starting with
a syscall_trace_enter call, which appears to be the second one
and causes that extra syscall stop you observe with 32-bit tracees
running on 64-bit kernels.


-- 
ldv