Re: KGTP (Linux debugger and tracer) 20130508 release (add single step support)

[Hui Zhu <teawater at gmail dot com>]

Hi,

I make a video to introduce how to use KGTP debug the Linux kernel of Android.
Please goto http://youtu.be/_UGN2j8Ctg0 or
http://www.tudou.com/programs/view/FjkQ6HhPnfE/ see the English
version.
Or goto http://www.tudou.com/programs/view/qCumSPhByFI/ or
http://youtu.be/9YMpAvsl37I see the Chinese version.

Thanks,
Hui

On Wed, May 8, 2013 at 5:41 PM, Hui Zhu <teawater@gmail.com> wrote:
> Hi guys,
>
> KGTP (http://code.google.com/p/kgtp/) is a flexible, lightweight and
> realtime Linux debugger and tracer.
> To use it, you don't need patch or rebuild the Linux kernel. Just
> build KGTP module and insmod it is OK.
>
> Please go to http://code.google.com/p/kgtp/wiki/HOWTO or
> http://code.google.com/p/kgtp/wiki/HOWTO (Chinese) to get more info
> about howto use KGTP.
>
> Please goto https://code.google.com/p/kgtp/wiki/HOWTO#Table_of_different_between_GDB_debug_normal_program_and_KGTP
> or https://code.google.com/p/kgtp/wiki/HOWTOCN#GDB调试普通程序和KGTP的区别表;
> (Chinese) get the table of different between GDB debug normal program
> and KGTP if you have experience using GDB debug normal program.
>
> Now, KGTP 20130508 release.
> You can get the package for it from
> http://kgtp.googlecode.com/files/kgtp_20130508.tar.bz2
> or
> svn co https://kgtp.googlecode.com/svn/tags/20130508
>
> The main change of this release is complete the support of
> while-stepping.  KGTP can let Linux kernel do single step now.
> Please note that while-stepping is just support by X86 and X86_64 now.
> Howto use while-stepping:
> while-stepping is a special tracepoint action that include some actions with it.
> When tracepoints that its actions include "while-stepping n" execute,
> it will do n times single steps and executes the actions of
> while-stepping. For example:
> trace vfs_read
> #Because single step will make system slow, so use passcount or
> condition to limit the execution times of tracepoint is better.
> passcount 1
>   commands
>     collect $bt
>     collect $step_count
>     #do 2000 times single steps.
>     while-stepping 2000
>       #Following part is actions of "while-stepping 2000".
>       #Because step maybe execute to other functions, so does not
> access local variables is better.
>       collect $bt
>       collect $step_count
>     end
>   end
> You can switch KGTP to replay mode to select all the traceframe of a
> while-stepping tracepoint with GDB execution and reverse-execution
> commands. For example:
> Use tfind select one the traceframe of a while-stepping tracepoint.
> (gdb) tfind
> Found trace frame 0, tracepoint 1
> #0  vfs_read (file=0xffff8801f7bd4c00, buf=0x7fff74e4edb0 <Address
> 0x7fff74e4edb0 out of bounds>, count=16,
>     pos=0xffff8801f4b45f48) at /build/buildd/linux-3.2.0/fs/read_write.c:365
> 365     {
> Following commands will swith KGTP to replay mode.
>
> (gdb) monitor replay
> (gdb) tfind -1
> No longer looking at any trace frame
> #0  vfs_read (file=0xffff8801f7bd4c00, buf=0x7fff74e4edb0 <Address
> 0x7fff74e4edb0 out of bounds>, count=16,
>     pos=0xffff8801f4b45f48) at /build/buildd/linux-3.2.0/fs/read_write.c:365
> 365     {
> Then you can use execution commands.
>
> (gdb) n
> 368             if (!(file->f_mode & FMODE_READ))
> (gdb) p file->f_mode
> $5 = 3
> Set breakpoints (Just valid in replay mode, will not affect Linux
> kernel execution).
>
> (gdb) b 375
> Breakpoint 2 at 0xffffffff81179b75: file
> /build/buildd/linux-3.2.0/fs/read_write.c, line 375.
> (gdb) c
> Continuing.
>
> Breakpoint 2, vfs_read (file=0xffff8801f7bd4c00, buf=0x7fff74e4edb0
> <Address 0x7fff74e4edb0 out of bounds>, count=16,
>     pos=0xffff8801f4b45f48) at /build/buildd/linux-3.2.0/fs/read_write.c:375
> 375             ret = rw_verify_area(READ, file, pos, count);
> (gdb) s
> rw_verify_area (read_write=0, file=0xffff8801f7bd4c00,
> ppos=0xffff8801f4b45f48, count=16)
>     at /build/buildd/linux-3.2.0/fs/read_write.c:300
> 300             inode = file->f_path.dentry->d_inode;
> Use reverse-execution commands.
>
> (gdb) rs
>
> Breakpoint 2, vfs_read (file=0xffff8801f7bd4c00, buf=0x7fff74e4edb0
> <Address 0x7fff74e4edb0 out of bounds>, count=16,
>     pos=0xffff8801f4b45f48) at /build/buildd/linux-3.2.0/fs/read_write.c:375
> 375             ret = rw_verify_area(READ, file, pos, count);
> (gdb) rn
> 372             if (unlikely(!access_ok(VERIFY_WRITE, buf, count)))
> GDB commands tstart, tfind or quit can auto close the replay mode.
>
> Please goto https://code.google.com/p/kgtp/wiki/HOWTO#Use_while-stepping_let_Linux_kernel_do_single_step
> or https://code.google.com/p/kgtp/wiki/HOWTOCN#使用while-stepping让Linux内核做单步;
> (Chinese version) get more info about it.
>
> Please goto http://code.google.com/p/kgtp/wiki/UPDATE get more info
> about this release.
>
> According to the comments of Christoph, Geoff and Andi.  I make lite
> patch for review.  Please goto https://lkml.org/lkml/2012/5/9/90 to
> see it.
>
> Thanks,
> Hui