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[Bug testsuite/4794] backtrace of yyy_func3 and print_stack of yyy_func3 fails on ppc64.


------- Additional Comments From srinivasa at in dot ibm dot com  2008-01-17 12:40 -------
I have investigated further on this. 
  Stack generating function __stp_stack_print() looks similar dump_stack() and 
I found that, this problem is present when we call dump_stack() from kprobe 
handler.

Hence this problem could be due to, 
1) we might have stored the ip somewhere else in the stack and reading the 
different value. ( Hence regs->nip at the first frame shows the correct value 
and value read from the stack shows inavlid value)

2) We might have overwritten the ip value in that stack.

dump_stack() from kprobe handler.
=============================================
 LR = .yyy_func2+0x10/0x28 [systemtap_test_module2]
[c0000000355dbab0] [0000000000000080] 0x80 (unreliable)
[c0000000355dbb30] [d0000000006e006c] .yyy_func1+0x10/0x28 
[systemtap_test_module2]
[c0000000355dbbb0] [d000000000790164] .stm_write_cmd+0xbc/0x440 
[systemtap_test_module1]
[c0000000355dbc40] [c000000000141cbc] .proc_reg_write+0xc0/0x100
[c0000000355dbcf0] [c0000000000f4dc0] .vfs_write+0xf8/0x1c4
[c0000000355dbd90] [c0000000000f57c0] .sys_write+0x4c/0x8c
[c0000000355dbe30] [c000000000008734] syscall_exit+0x0/0x40
========================================

stack generated by systemtap.
==========================================
 0xd0000000006e000c : .yyy_func3+0x0/0x28 
[systemtap_test_module2]0xc0000000355dbab0
[0xc0000000355db838] [0x00000000000004d2] 0x00000000000004d2  (unreliable)
[0xc0000000355dbab0] [0x0000000000000080] 0x0000000000000080
[0xc0000000355dbb30] [0xd0000000006e006c] 0xd0000000006e006c : .yyy_func1+0x10/
0x28 [systemtap_test_module2]
[0xc0000000355dbbb0] [0xd000000000790164] 0xd000000000790164
 : .stm_write_cmd+0xbc/0x0 [systemtap_test_module1]
[0xc0000000355dbc40] [0xc000000000141cbc] 0xc000000000141cbc
 : .proc_reg_write+0xc0/0x100 []
[0xc0000000355dbcf0] [0xc0000000000f4dc0] 0xc0000000000f4dc0 : .vfs_write+0xf8/
0x1c4 []
[0xc0000000355dbd90] [0xc0000000000f57c0] 0xc0000000000f57c0 : .sys_write+0x4c/
0x8c []
[0xc0000000355dbe30] [0xc000000000008734] 0xc000000000008734 : syscall_exit+0x0/
0x40 []
--- Exception: c00 at 0x000000000ff1a758
===============================

-- 


http://sourceware.org/bugzilla/show_bug.cgi?id=4794

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