[superh-gnu-discuss] Problems with gdbserver

[Phil Edworthy]

> -----Original Message-----
> From: Phil Edworthy
> Sent: 01 October 2010 08:20
> To: 'Paul Mundt'
> Cc: superh-gnu-discuss at codesourcery.com
> Subject: RE: [superh-gnu-discuss] Problems with gdbserver
> 
> Hi Paul,
> 
> > -----Original Message-----
> > From: Paul Mundt [mailto:lethal at linux-sh.org]
> > Sent: 30 September 2010 17:46
> > To: Phil Edworthy
> > Cc: superh-gnu-discuss at codesourcery.com
> > Subject: Re: [superh-gnu-discuss] Problems with gdbserver
> >
> > On Thu, Sep 30, 2010 at 04:35:55PM +0100, Phil Edworthy wrote:
> > > Unable to handle kernel NULL pointer dereference at virtual address
> > 00000084
> > > pc = 88004260
> > > *pde = 8f197000
> > > Oops: 0001 [#18]
> > > last sysfs file: /sys/class/vc/vcs3/dev
> > > Modules linked in:
> > >
> > > Pid : 607, Comm:                gdbserver
> > > CPU : 0                 Tainted: G      D      (2.6.35 #1)
> > >
> > > PC  : 88004260 SP  : 8f1e1f88 SR  : 40008100 TEA : 296608c0
> > > R0  : 00000000 R1  : 00000000 R2  : 00000000 R3  : fffffffc
> > > R4  : 8f0676c0 R5  : 00000006 R6  : 00000084 R7  : 00000000
> > > R8  : 8f0676c0 R9  : 00000006 R10 : 00000000 R11 : 000000e0
> > > R12 : 00000000 R13 : 00000004 R14 : 7bf21a40
> > > MACH: 00000004 MACL: 5c405562 GBR : 296f5470 PR  : 8801dabc
> > >
> > > Call trace:
> > >  [<8801dabc>] 0x8801dabc
> > >  [<8800725a>] 0x8800725a
> > >  [<8801da20>] 0x8801da20
> > >
> > Can you attach your System.map for this kernel? What does addr2line
> > report for the PC?
> 
> Only after I sent this was it pointed out to me that the null ptr is being
> picked up in the kernel.
> 
> System.map attached.
> 
> $ sh-linux-gnu-addr2line -f -e vmlinux 88004260
> arch_ptrace
> ??:0
> 
> The call trace corresponds to:
> 0x8801dabc  sys_ptrace    ??:0
> 0x8800725a  syscall_call  probe.c:0
> 0x8801da20  sys_ptrace    ??:0

I traced it back a bit further in arch/sh/kernel/ptrace_32.c: arch_ptrace.
When sent a PTRACE_POKEUSR request for user space, child->thread.xstate is
null.

BTW, this also happens on a stock 2.6.35 kernel

Thanks
Phil