Question: strace detach as soon as attach

[Jovi Zhang]

On Fri, Oct 19, 2012 at 4:28 PM, Jovi Zhang <bookjovi at gmail.com> wrote:

> Hi,
>
> I encounter a problem in strace 4.5.19 version(for arm), strace detach as
> soon as attach.
>
> I got below old bug report in this mailing list, which have same problem
> with my situation.
>
>
> http://www.mail-archive.com/strace-devel@lists.sourceforge.net/msg01669.html
>
> Unfortunately, I don't get answer on that bug report, so is there anyone
> can tell me that this bug is already fixed in strace or kernel?
> Thanks!
>
>  [bug] strace detach as soon as attach
>
> OneGun Lee
> Wed, 07 Jul 2010 23:13:48 -0700
>
> Hi, all
>
> I tried to use strace-4.5.15(and .20) on linux-2.6.29.4, arm-cortex-a8.
>
> but strace was detached as soon as was attached one process.
>
> # strace -p 1711 -d
> Process 1711 attached - interrupt to quit
>  [wait(0x137f) = 1711]
> pid 1711 stopped, [SIGSTOP]
>  [wait(0x57f) = 1711]
> pid 1711 stopped, [SIGTRAP]
> Process 1711 detached
>
> So, I debuged strace.
> After attach, strace try to ptrace(PTRACE_PEEKTEXT) and input param
> is kernel space's address(0xFFFFxxxx).
> This kernel space address's data is scno(restart_syscall).
>
> address = 0xffff051c, data = 0xef900000(restart_syscall)
>
> This command is sent kernel mode.
> and than, arch_ptrace,kernel function, try to get data this address.
> so this function call access_process_vm() -> get_user_pages().
>
> get_user_pages() function make error because start address param is kernel
> space's address.
> so strace is detached.
> I think that it is bug to need fix.
> If address to want to get data is in kernel space, access_process_vm() just
> read data. don't call get_user_pages().
> Or
> strace have not try to peek data, if address is in kernel space.
>
> How do you think about this problem?
>
> It seems that there had one patch target for fix this issue, but I checked
git history of strace, I don't find this patch merged, so it means that
this
issue still on there.

http://marc.info/?l=strace&m=128703091611617
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