On Wed, 2017-02-15 at 01:01 +0900, Masami Hiramatsu wrote:
> On Tue, 14 Feb 2017 13:47:07 +0000
> "Jon Medhurst (Tixy)" <t...@linaro.org> wrote:
>
> > On Tue, 2017-02-14 at 10:32 +0000, Jon Medhurst (Tixy) wrote:
> > > On Tue, 2017-02-14 at 00:05 +0900, Masami Hiramatsu wrote:
> > > > This is arm port of commit 737480a0d525 ("kprobes/x86:
> > > > Fix the return address of multiple kretprobes").
> > > >
> > > > Fix the return address of subsequent kretprobes when multiple
> > > > kretprobes are set on the same function.
> > > >
> > > > For example:
> > > >
> > > > # cd /sys/kernel/debug/tracing
> > > > # echo "r:event1 sys_symlink" > kprobe_events
> > > > # echo "r:event2 sys_symlink" >> kprobe_events
> > > > # echo 1 > events/kprobes/enable
> > > > # ln -s /tmp/foo /tmp/bar
> > > >
> > > > (without this patch)
> > > >
> > > > # cat trace | grep -v ^#
> > > > ln-82 [000] dn.2 68.446525: event1:
> > > > (kretprobe_trampoline+0x0/0x18 <- SyS_symlink)
> > > > ln-82 [000] dn.2 68.447831: event2:
> > > > (ret_fast_syscall+0x0/0x1c <- SyS_symlink)
> > > >
> > > > (with this patch)
> > > >
> > > > # cat trace | grep -v ^#
> > > > ln-81 [000] dn.1 39.463469: event1:
> > > > (ret_fast_syscall+0x0/0x1c <- SyS_symlink)
> > > > ln-81 [000] dn.1 39.464701: event2:
> > > > (ret_fast_syscall+0x0/0x1c <- SyS_symlink)
> > > >
> > > > Signed-off-by: Masami Hiramatsu <mhira...@kernel.org>
> > > > Cc: KUMANO Syuhei <kumano.p...@gmail.com>
> > > > ---
> > >
> > > I don't fully understand this function, but I've checked that the ARM
> > > version now matches the x86 version (apart from the x86 specific
> > > register fixup and some comments). So, FWIW
> > >
> > > Acked-by: Jon Medhurst <t...@linaro.org>
> > >
> > > I ran the before and after test case in the commit log on ARM and
> > > verified the result is correct. I also tried running the ARM kprobe
> > > tests with these 3 fixes but the tests fail. However, they also fail
> > > without any of these changes, so I'll investigate that further...
> >
> > Bisecting the issue led me back to Linux 4.5 and commit 25362dc496ed
> > ("ARM: 8501/1: mm: flip priority of CONFIG_DEBUG_RODATA")
> >
> > This sets CONFIG_DEBUG_RODATA to be enabled by default. If I disable
> > that on 4.10-rc4, with the three patches in this series, then the ARM
> > kprobes tests pass OK.
> >
> > I'll stick the DEBUG_RODATA issue on my todo list (it's been around for
> > a year, so can probably wait a little longer).
>
> Hmm, I'm running arm kernel on qemu, which maybe the reason why
> the test case passed in my environment, since my kconfig also sets
> CONFIG_DEBUG_RODATA=y.
>
> BTW, would you see that any kprobe_events didn't work with
> CONFIG_DEBUG_RODATA=y? (what the failure messages were?)
The tests I'm running are the ARM specific tests that are enabled by
CONFIG_ARM_KPROBES_TEST=y. I'm running the tests on real multicore ARM
hardware (Versatile Express with a TC2 CoreTile)
For me, sometimes the first test gave:
Beginning kprobe tests...
Probe ARM code
kprobe
FAIL: test regs not OK
Other times, for the specific instruction emulation tests they return
FAIL: test_before_handler not run
Not sure how much of the diagnostic appear without setting the tests to
be verbose, which I do with:
sed -e 's/VERBOSE 0/VERBOSE 1/' -i arch/arm/probes/kprobes/test-core.h
Whilst writing a reply, I looked at the test code in
arch/arm/probes/kprobes/test-core.c (which I wrote some years ago) and
there is possibly a clue staring at us in the comments at the top of the
file...
*
* The above would expand to assembler looking something like:
*
* @ TESTCASE_START
* bl __kprobes_test_case_start
* .pushsection .rodata
* "10:
* .ascii "mov r0, r7" @ text title for test case
* .byte 0
* .popsection
* @ start of inline data...
* .word 10b @ pointer to title in .rodata
section
Note the ".pushsection .rodata" (though I don't see an immediate obvious
reason why that would cause a problem. It certainly seems likely that
the problem is with the ARM test code rather than actual kprobe
implementation itself.
Like I said, this issue has been there for a year or more, so I wasn't
planning on spending time on it for a few more days yet whilst I get on
with other urgent matters.
--
Tixy
Basically, m
