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varwatch.txt
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varwatch.stp - Watch a Variable Changing Value in a Thread This script places a set of probes (specified by $1), each of which monitors the state of some context $variable expression (specified by $2). Whenever the value changes, with respect to the active thread, the event is traced. $ stap -w varwatch.stp 'kernel.function("sys_*@fs/open.c:*")' \ '$$parms' -c "ls > /dev/null" sh[32715] kernel.function("SyS_access@fs/open.c:395") $$parms: filename=0x7f340e5cb750 mode=0x4 sh[32715] kernel.function("SyS_open@fs/open.c:992") $$parms: filename=0x7f340e5ca048 flags=0x80000 mode=0x1 sh[32715] kernel.function("SyS_close@fs/open.c:1053") $$parms: fd=0x3 sh[32715] kernel.function("SyS_close@fs/open.c:1058") $$parms: fd=? sh[32715] kernel.function("SyS_open@fs/open.c:992") $$parms: filename=0x7f340e7c22cb flags=0x80000 mode=0x7f340e7d0168 sh[32715] kernel.function("SyS_close@fs/open.c:1053") $$parms: fd=0x3 sh[32715] kernel.function("SyS_close@fs/open.c:1058") $$parms: fd=? sh[32715] kernel.function("SyS_open@fs/open.c:992") $$parms: filename=0x7f340e7c9e89 flags=0x80000 mode=0x7f340e7d0168 sh[32715] kernel.function("SyS_close@fs/open.c:1053") $$parms: fd=0x3 sh[32715] kernel.function("SyS_close@fs/open.c:1058") $$parms: fd=? sh[32715] kernel.function("SyS_open@fs/open.c:992") $$parms: filename=0x7f340e7caf39 flags=0x80000 mode=0x7f340e7d0168 sh[32715] kernel.function("SyS_close@fs/open.c:1053") $$parms: fd=0x3 sh[32715] kernel.function("SyS_close@fs/open.c:1058") $$parms: fd=? sh[32715] kernel.function("SyS_open@fs/open.c:992") $$parms: filename=0x4a8ddf flags=0x802 mode=0x6eb0c8 sh[32715] kernel.function("SyS_close@fs/open.c:1053") $$parms: fd=0x3 sh[32715] kernel.function("SyS_close@fs/open.c:1058") $$parms: fd=? sh[32715] kernel.function("SyS_open@fs/open.c:992") $$parms: filename=0x7f340df403d0 flags=0x80000 mode=0x7f340e17a768 sh[32715] kernel.function("SyS_close@fs/open.c:1053") $$parms: fd=0x3 sh[32715] kernel.function("SyS_close@fs/open.c:1058") $$parms: fd=? sh[32715] kernel.function("SyS_open@fs/open.c:992") $$parms: filename=0x7f340df3d2ea flags=0x80000 mode=0x1b6 sh[32715] kernel.function("SyS_close@fs/open.c:1053") $$parms: fd=0x3 sh[32715] kernel.function("SyS_close@fs/open.c:1058") $$parms: fd=? sh[32715] kernel.function("SyS_open@fs/open.c:992") $$parms: filename=0x7f340df3ea80 flags=0x0 mode=0x0 sh[32715] kernel.function("SyS_close@fs/open.c:1053") $$parms: fd=0x3 sh[32715] kernel.function("SyS_close@fs/open.c:1058") $$parms: fd=? [...] The output monitors the parameters to functions sys_*. This can be narrowed down to follow a certain function, in this example maybe sys_close, throughout a process's lifetime.