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Diffstat (limited to 'stapprobes.3stap.in')
| -rw-r--r-- | stapprobes.3stap.in | 52 |
1 files changed, 52 insertions, 0 deletions
diff --git a/stapprobes.3stap.in b/stapprobes.3stap.in index 8b39545e..23de56b0 100644 --- a/stapprobes.3stap.in +++ b/stapprobes.3stap.in @@ -660,6 +660,55 @@ and a string of name=value pairs for all parameters of the tracepoint is available in .BR $$vars " or " $$parms . +.SS HARDWARE BREAKPOINTS +This family of probes is used to set hardware watchpoints for a given + (global) kernel symbol. The probes take three components as inputs : + +1. The +.BR virtual address / name +of the kernel symbol to be traced is supplied as argument to this class +of probes. ( Probes for only data segment variables are supported. Probing +local variables of a function cannot be done.) + +2. Nature of access to be probed : +a. +.I .write +probe gets triggered when a write happens at the specified address/symbol +name. +b. +.I rw +probe is triggered when either a read or write happens. + +3. +.BR .length +(optional) +Users have the option of specifying the address interval to be probed +using "length" constructs. The user-specified length gets approximated +to the closest possible address length that the architecture can +support. If the specified length exceeds the limits imposed by +architecture, an error message is flagged and probe registration fails. +Wherever 'length' is not specified, the translator requests a hardware +breakpoint probe of length 1. It should be noted that the "length" +construct is not valid with symbol names. + +Following constructs are supported : +.SAMPLE +probe kernel.data(ADDRESS).write +probe kernel.data(ADDRESS).rw +probe kernel.data(ADDRESS).length(LEN).write +probe kernel.data(ADDRESS).length(LEN).rw +probe kernel.data("SYMBOL_NAME").write +probe kernel.data("SYMBOL_NAME").rw +.ESAMPLE + +This set of probes make use of the debug registers of the processor, +which is a scarce resource. (4 on x86 , 1 on powerpc ) The script +translation flags a warning if a user requests more hardware breakpoint probes +than the limits set by architecture. For example,a pass-2 warning is flashed +when an input script requests 5 hardware breakpoint probes on an x86 +system while x86 architecture supports a maximum of 4 breakpoints. +Users are cautioned to set probes judiciously. + .SH EXAMPLES .PP Here are some example probe points, defining the associated events. @@ -696,6 +745,9 @@ refers to the statement of line 2917 within "kernel/sched.c". kernel.statement("bio_init@fs/bio.c+3") refers to the statement at line bio_init+3 within "fs/bio.c". .TP +kernel.data("pid_max").write +refers to a hardware preakpoint of type "write" set on pid_max +.TP syscall.*.return refers to the group of probe aliases with any name in the third position |