Re: [Xenomai-help] page faults

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

Jeff Weber wrote:
 > On Monday 16 April 2007 15:05, Philippe Gerum wrote:
 > 
 > > Could you disassemble the code around location 0x80fb8c5?
 > The latest version of my code has moved the the addresses a bit:
 > Xenomai: Switching mythread to secondary mode after exception #14 from user-space at 0x80fb8cd (pid 3590)
 > 
 > (gdb) disas
 > Dump of assembler code for function _ZN4AMSC8CRtDequeIcE9push_backERKc:
 > 0x080fb8b4 <_ZN4AMSC8CRtDequeIcE9push_backERKc+0>:      push   %ebp
 > 0x080fb8b5 <_ZN4AMSC8CRtDequeIcE9push_backERKc+1>:      mov    %esp,%ebp
 > 0x080fb8b7 <_ZN4AMSC8CRtDequeIcE9push_backERKc+3>:      sub    $0x8,%esp
 > 0x080fb8ba <_ZN4AMSC8CRtDequeIcE9push_backERKc+6>:      mov    0x8(%ebp),%edx
 > 0x080fb8bd <_ZN4AMSC8CRtDequeIcE9push_backERKc+9>:      mov    0x8(%ebp),%eax
 > 0x080fb8c0 <_ZN4AMSC8CRtDequeIcE9push_backERKc+12>:     mov    0x8(%eax),%eax
 > 0x080fb8c3 <_ZN4AMSC8CRtDequeIcE9push_backERKc+15>:     mov    (%edx),%edx
 > 0x080fb8c5 <_ZN4AMSC8CRtDequeIcE9push_backERKc+17>:     add    %eax,%edx
 > 0x080fb8c7 <_ZN4AMSC8CRtDequeIcE9push_backERKc+19>:     mov    0xc(%ebp),%eax
 > 0x080fb8ca <_ZN4AMSC8CRtDequeIcE9push_backERKc+22>:     movzbl (%eax),%eax
 > 0x080fb8cd <_ZN4AMSC8CRtDequeIcE9push_backERKc+25>:     mov    %al,(%edx)
 > 0x080fb8cf <_ZN4AMSC8CRtDequeIcE9push_backERKc+27>:     mov    0x8(%ebp),%eax
 > 0x080fb8d2 <_ZN4AMSC8CRtDequeIcE9push_backERKc+30>:     add    $0x8,%eax
 > 0x080fb8d5 <_ZN4AMSC8CRtDequeIcE9push_backERKc+33>:     mov    %eax,0x4(%esp)
 > 0x080fb8d9 <_ZN4AMSC8CRtDequeIcE9push_backERKc+37>:     mov    0x8(%ebp),%eax
 > 0x080fb8dc <_ZN4AMSC8CRtDequeIcE9push_backERKc+40>:     mov    %eax,(%esp)
 > 0x080fb8df <_ZN4AMSC8CRtDequeIcE9push_backERKc+43>:     call   0x80fcb18 <_ZN4AMSC8CRtDequeIcE3incERi>
 > 
 > >
 > > > as well as the delivery of SIGXCPU to my application (at my request).
 > > >
 > > > How do I prevent this page fault?
 > > >
 > > > Is this issue covered by the recent NOCOW activity?
 > >
 > > Possibly. You need I-pipe 1.7-03 and Xenomai >= v2.3.1 to get the
 > > ondemand mapping scheme disabled by the nucleus when your thread starts.
 > I am not familiar with the purpose and implementation of the NOCOW patch.
 > How would the patch affect my page fault issue?

If the fault you observe is due to an access to some memory after a call
to fork or one of its derivative (such as system, popen, etc...), the
patch would have copied the whole real-time process address space at
fork time instead of setting up COW mappings.

-- 


					    Gilles Chanteperdrix.