diff options
| -rw-r--r-- | NEWS | 6 | ||||
| -rw-r--r-- | stap.1.in | 42 |
2 files changed, 48 insertions, 0 deletions
@@ -1,5 +1,11 @@ * What's new in version 0.9 +- Typecasting is now supported using the @cast operator. A script can + define a pointer type for a "long" value, and then access type members + using the same syntax as with $target variables. For example, this will + retrieve the parent pid from a kernel task_struct: + @cast(pointer, "task_struct", "kernel")->parent->pid + - process().mark() probes are now possible to trace static user space markers put in programs with the STAP_PROBE macro using the new sys/sdt.h include file. This also provides dtrace compatible markers @@ -755,6 +755,46 @@ probe end { } .ESAMPLE +.SS TYPECASTING +Once a pointer has been saved into a script integer variable, the +translator loses the type information necessary to access members from +that pointer. Using the +.I @cast() +operator tells the translator how to read a pointer. +.SAMPLE +@cast(p, "type_name"[, "module"])->member +.ESAMPLE +.PP +This will interpret +.I p +as a pointer to a struct/union named +.I type_name +and dereference the +.I member +value. The optional +.I module +tells the translator where to look for information about that type. If +the module is not specified, it will default either to the probe module +for dwarf probes, or to "kernel" for functions and all other probes +types. +.PP +When in guru mode, the translator will also allow scripts to assign new +values to members of typecasted pointers. +.PP +Typecasting is also useful in the case of +.I void* +members whose type may be determinable at runtime. +.SAMPLE +probe foo { + if ($var->type == 1) { + value = @cast($var->data, "type1")->bar + } else { + value = @cast($var->data, "type2")->baz + } + print(value) +} +.ESAMPLE + .SS EMBEDDED C When in guru mode, the translator accepts embedded code in the script. Such code is enclosed between @@ -1076,6 +1116,8 @@ probe specifications that refer to inline functions .IP \(bu 4 statements that refer to $target variables .IP \(bu 4 +statements that refer to @cast() variables +.IP \(bu 4 tapset-defined variables defined using any of the above constructs. In particular, at this writing, the prologue blocks for certain aliases in the syscall tapset |