IBM AIX Continuous Availability Features - IBM Redbooks

strlen() at 0xd010da00
_doprnt(??, ??, ??) at 0xd0126350
printf(0x200003f4, 0x30000000, 0xffffffff, 0x2ff47600, 0x0, 0x0, 0x0, 0x0) at
0xd011eabc
main(argc = 2, argv = 0x2ff22554), line 126 in "ukey1.c"
(dbx)q
#
Notice that a segmentation fault occurred at strlen(), which was trying to read shared memory
and calculate its size. Because read permission was not provided, it caused SIGSEGV.
Next, we gave the child process read (no-write) access to the shared memory segment and
executed the code as shown in Example 3-33.
Example 3-33 Program with read access to shared segment
# ./ukey1 read
parent:pagesize=4096
child:data=0x30000000
child :READ1 =[]
parent:READ1 =[]
parent:WRITE1=[ABCD]
# ls core
core
# dbx ukey1 core
Type 'help' for help.
[using memory image in core]
reading symbolic information ...
Segmentation fault in noname.strcpy [ukey1] at 0x10001004
0x10001004 (strcpy+0x4) 99030000 stb r8,0x0(r3)
(dbx) where
noname.strcpy() at 0x10001004
main(argc = 2, argv = 0x2ff2255c), line 127 in "ukey1.c"
(dbx)q
#
Notice that a segmentation fault occurred at the strcpy() function, which was trying to write to
shared memory. The strlen() function did not fail this time, because we gave read access to
the shared page. However, the child process does not have write access to strcpy(), which
caused SIGSEGV.
We executed the program by giving read and write access, as shown in Example 3-34 on
page 106.
Example 3-34 Program gets read and write access to shared segment
# ./ukey1 readwrite
parent:pagesize=4096
child:data=0x30000000
child :READ1 =[]
child :WRITE1=[abcd]
parent:READ1 =[abcd]
parent:WRITE1=[ABCD]
child :READ2 =[abcdABCD]
child :WRITE2=[efgh]
106 IBM AIX Continuous Availability Features