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Some questions about kernel stack backtrace when using SystemTap
- From: Nan Xiao <xiaonan830818 at gmail dot com>
- To: systemtap at sourceware dot org
- Date: Thu, 12 Nov 2015 16:01:30 +0800
- Subject: Some questions about kernel stack backtrace when using SystemTap
- Authentication-results: sourceware.org; auth=none
Hi all,
I am trying to print kernel stack backtrace when executing
"generic_file_open" function.
And the output confuses me:
# stap -e 'probe kernel.function("generic_file_open") {if (execname()
== "cat") print_backtrace() print("\n");}'
0xffffffff80152140 : generic_file_open+0x0/0x20 [kernel]
0xffffffff800082e9 : dump_trace+0x79/0x1a0 [kernel]
0xffffffffa085ab1d [stap_92f96ed1154d2edf7d3c12071ce7fd2f_6907+0x8b1d/0x0]
0xffffffffa085ad79 [stap_92f96ed1154d2edf7d3c12071ce7fd2f_6907+0x8d79/0x0]
0xffffffff804bca5d : kprobe_ftrace_handler+0xcd/0x120 [kernel]
0xffffffff800c7e56 : ftrace_ops_list_func+0xf6/0x110 [kernel]
0xffffffff804c1562 : ftrace_regs_call+0x5/0x77 [kernel]
0xffffffff80152140 : generic_file_open+0x0/0x20 [kernel] (inexact)
0xffffffff80152140 : generic_file_open+0x0/0x20 [kernel] (inexact)
0xffffffff80152145 : generic_file_open+0x5/0x20 [kernel] (inexact)
0xffffffff80152423 : do_dentry_open+0x143/0x2a0 [kernel] (inexact)
0xffffffff8015f509 : __inode_permission+0x59/0xb0 [kernel] (inexact)
0xffffffff801634db : do_last+0x21b/0x1290 [kernel] (inexact)
0xffffffff8014599a : kmem_cache_alloc_trace+0x1ea/0x470 [kernel] (inexact)
0xffffffff8016460b : path_openat+0xbb/0x640 [kernel] (inexact)
0xffffffff80165aba : do_filp_open+0x3a/0x90 [kernel] (inexact)
0xffffffff80172767 : __alloc_fd+0x87/0x140 [kernel] (inexact)
0xffffffff80153b29 : do_sys_open+0x129/0x220 [kernel] (inexact)
0xffffffff804c1777 : system_call_fastpath+0x16/0x1b [kernel] (inexact)
My questions are as follow:
(1) What is "(inexact)" meaning?
(2) I find some stack frames like this:
0xffffffffa085ab1d [stap_92f96ed1154d2edf7d3c12071ce7fd2f_6907+0x8b1d/0x0]
0xffffffffa085ad79 [stap_92f96ed1154d2edf7d3c12071ce7fd2f_6907+0x8d79/0x0]
Why aren't they human understandable function names?
Thanks in advance!
Best Regards
Nan Xiao