Messages in this thread | | | From | Hui Zhu <> | Date | Wed, 8 May 2013 17:41:03 +0800 | Subject | KGTP (Linux debugger and tracer) 20130508 release (add single step support) |
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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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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