IBM AIX Continuous Availability Features - IBM Redbooks

Load the kernel extension so that a system call can use it form user mode, as shown in
Example 3-27.
Example 3-27 Loading kernel extension using tool “service”
# ./service --load kkey_set64
Preserving 2378 bytes of symbol table [kkey_set64]
[kkey_set64] loaded successfully kernel mid=[546676736]
Run myprog without any argument, which means it will run the kernel extension (syscall) with
the appropriate protection gate {{KKEYSET_KERNEXT}+KKEY_VMM}. Because the private
heap of the kernel extension has been protected by KKEY_VMM, you can access it and the
system call will return without any DSI/crash.
Execute the user-level program that will call the kernel system call with protection gate
enabled with KKEY_VMM, as shown in Example 3-28.
Example 3-28 First iteration with KKEY_VMM
#./myprog
Testing Kernel Storage key
Current hardware keyset =0008000000000000
hardware keyset after KERNEXT =F00F000000000000
hardware keyset after KKEY_VMM=F00C000000000000
Now execute the user-level program that will call the kernel system call with a protection gate
without KKEY_VMM key in its keyset (see Example 3-29 on page 96). This will cause the
kernel to crash. Running myprog with argument>2 will do that.
Because the private heap of the kernel extension has not been protected by KKEY_VMM, a
DSI will result and the kernel will crash. Keep in mind that exception type EXCEPT_SKEY
cannot be caught with setjmpx(), so the kernel programmer cannot catch EXCEPT_SKEY
using setjmpx().
Note: There are kernel services provided for catching storage-key exceptions. However,
their use is not recommended and they are provided only for testing purposes.
Example 3-29 Second iteration without KKEY_VMM
# ./myprog 1
Current hardware keyset =0008000000000000
hardware keyset after KERNEXT =F00F000000000000
hardware keyset after KKEY_VMM=F00C000000000000
hardware keyset w/o KKEY_VMM =F00F000000000000
Data Storage Interrupt - PROC
.kkey_test+0002C8 stb r3,A(r4)
r3=000000000000000A,A(r4)=F10006C00134A00A
KDB(6)>
When you are debugging in kernel mode (see Example 3-30), you can see the value of the
AMR (current hardware key or protection gate), the current process which caused the
exception, and the exception type. Refer to 3.7.8, “Kernel debugger commands” on page 108
96 IBM AIX Continuous Availability Features