linux-kernel - Re: Crash in msm serial on dragonboard with ftrace bootargs

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Date:   Thu, 18 Oct 2018 09:17:06 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
Cc:     Stephen Boyd <sboyd@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Andy Gross <andy.gross@...aro.org>,
        David Brown <david.brown@...aro.org>,
        Jiri Slaby <jslaby@...e.com>,
        Kees Cook <keescook@...omium.org>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        Geliang Tang <geliangtang@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Pramod Gurav <gpramod@...eaurora.org>,
        linux-arm-msm@...r.kernel.org, linux-soc@...r.kernel.org,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Vivek Gautam <vivek.gautam@...eaurora.org>,
        Sibi Sankar <sibis@...eaurora.org>
Subject: Re: Crash in msm serial on dragonboard with ftrace bootargs

On Thu, 18 Oct 2018 10:51:18 +0530
Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org> wrote:

> > So something else is causing an issue besides just msm_read.
> > 
> > Can you do an objdump -dr of the entire vmlinux binary and gzip it and
> > post it somewhere. Not sure if it would be too big to email. You could
> > try sending it to me privately. I'd like to see the binary that you are
> > using.
> >   
> 
> I have sent the objdump and dot config to you privately.

Thanks. I don't see anything that pops out, but then again, my arm asm
foo is very rusty (it has been literally decades since I did any arm
asm). I wonder if it could simply be a timing issue?

ffff0000086eb538 <msm_read.isra.1>:
ffff0000086eb538:       a9be7bfd        stp     x29, x30, [sp,#-32]!
ffff0000086eb53c:       910003fd        mov     x29, sp
ffff0000086eb540:       a90153f3        stp     x19, x20, [sp,#16]
ffff0000086eb544:       aa0003f4        mov     x20, x0
ffff0000086eb548:       2a0103f3        mov     w19, w1
ffff0000086eb54c:       aa1e03e0        mov     x0, x30
ffff0000086eb550:       97e6bae4        bl      ffff00000809a0e0 <_mcount>

The above is changed to nop on boot, but then to:

	bl ftrace_caller

When ftrace is enabled.

ffff0000086eb554:       8b334280        add     x0, x20, w19, uxtw
ffff0000086eb558:       b9400000        ldr     w0, [x0]
ffff0000086eb55c:       a94153f3        ldp     x19, x20, [sp,#16]
ffff0000086eb560:       a8c27bfd        ldp     x29, x30, [sp],#32
ffff0000086eb564:       d65f03c0        ret



ffff00000809a0e4 <ftrace_caller>:
ffff00000809a0e4:       a9bf7bfd        stp     x29, x30, [sp,#-16]!
ffff00000809a0e8:       910003fd        mov     x29, sp
ffff00000809a0ec:       d10013c0        sub     x0, x30, #0x4
ffff00000809a0f0:       f94003a1        ldr     x1, [x29]
ffff00000809a0f4:       f9400421        ldr     x1, [x1,#8]
ffff00000809a0f8:       d1001021        sub     x1, x1, #0x4

ffff00000809a0fc <ftrace_call>:
ffff00000809a0fc:       d503201f        nop

The above nop gets patched to:

	bl ftrace_ops_no_ops

Which will iterate through all the registered functions.


ffff00000809a100 <ftrace_graph_call>:
ffff00000809a100:       d503201f        nop

The above only gets set when function graph tracer is enabled, which it
is not in this case.

ffff00000809a104:       a8c17bfd        ldp     x29, x30, [sp],#16
ffff00000809a108:       d65f03c0        ret


Anyone see any problems here?

-- Steve