1 \documentclass{article}
2 \usepackage[fancyhdr,pdf]{latex2man}
8 \begin{Name}{3}{libunwind-ptrace}{David Mosberger-Tang}{Programming Library}{ptrace() support in libunwind}libunwind-ptrace -- ptrace() support in libunwind
13 \File{\#include $<$libunwind-ptrace.h$>$}\\
16 \Type{unw\_accessors\_t} \Var{\_UPT\_accessors};\\
18 \Type{void~*}\Func{\_UPT\_create}(\Type{pid\_t});\\
20 \Type{void} \Func{\_UPT\_destroy}(\Type{void~*});\\
23 \Type{int} \Func{\_UPT\_find\_proc\_info}(\Type{unw\_addr\_space\_t}, \Type{unw\_word\_t}, \Type{unw\_proc\_info\_t~*}, \Type{int}, \Type{void~*});\\
25 \Type{void} \Func{\_UPT\_put\_unwind\_info}(\Type{unw\_addr\_space\_t}, \Type{unw\_proc\_info\_t~*}, \Type{void~*});\\
27 \Type{int} \Func{\_UPT\_get\_dyn\_info\_list\_addr}(\Type{unw\_addr\_space\_t}, \Type{unw\_word\_t~*}, \Type{void~*});\\
29 \Type{int} \Func{\_UPT\_access\_mem}(\Type{unw\_addr\_space\_t}, \Type{unw\_word\_t}, \Type{unw\_word\_t~*}, \Type{int}, \Type{void~*});\\
31 \Type{int} \Func{\_UPT\_access\_reg}(\Type{unw\_addr\_space\_t}, \Type{unw\_regnum\_t}, \Type{unw\_word\_t~*}, \Type{int}, \Type{void~*});\\
33 \Type{int} \Func{\_UPT\_access\_fpreg}(\Type{unw\_addr\_space\_t}, \Type{unw\_regnum\_t}, \Type{unw\_fpreg\_t~*}, \Type{int}, \Type{void~*});\\
35 \Type{int} \Func{\_UPT\_get\_proc\_name}(\Type{unw\_addr\_space\_t}, \Type{unw\_word\_t}, \Type{char~*}, \Type{size\_t}, \Type{unw\_word\_t~*}, \Type{void~*});\\
37 \Type{int} \Func{\_UPT\_resume}(\Type{unw\_addr\_space\_t}, \Type{unw\_cursor\_t~*}, \Type{void~*});\\
41 The \Func{ptrace}(2) system-call makes it possible for a process to
42 gain access to the machine-state and virtual memory of \emph{another}
43 process. With the right set of call-back routines, it is therefore
44 possible to hook up \Prog{libunwind} to another process via
45 \Func{ptrace}(2). While it's not very difficult to do so directly,
46 \Prog{libunwind} further facilitates this task by providing
47 ready-to-use callbacks for this purpose. The routines and variables
48 implementing this facility use a name-prefix of \Func{\_UPT}, which is
49 stands for ``unwind-via-ptrace''.
51 An application that wants to use the \Func{\_UPT}-facility first needs
52 to create a new \Prog{libunwind} address-space that represents the
53 target process. This is done by calling
54 \Func{unw\_create\_addr\_space}(). In many cases, the application
55 will simply want to pass the address of \Var{\_UPT\_accessors} as the
56 first argument to this routine. Doing so will ensure that
57 \Prog{libunwind} will be able to properly unwind the target process.
58 However, in special circumstances, an application may prefer to use
59 only portions of the \Prog{\_UPT}-facility. For this reason, the
60 individual callback routines (\Func{\_UPT\_find\_proc\_info}(),
61 \Func{\_UPT\_put\_unwind\_info}(), etc.) are also available for direct
62 use. Of course, the addresses of these routines could also be picked
63 up from \Var{\_UPT\_accessors}, but doing so would prevent static
64 initialization. Also, when using \Var{\_UPT\_accessors}, \emph{all}
65 the callback routines will be linked into the application, even if
66 they are never actually called.
68 Next, the application can turn on ptrace-mode on the target process,
69 either by forking a new process, invoking \Const{PTRACE\_TRACEME}, and
70 then starting the target program (via \Func{execve}(2)), or by
71 directly attaching to an already running process (via
72 \Const{PTRACE\_ATTACH}). Either way, once the process-ID (pid) of the
73 target process is known, a \Prog{\_UPT}-info-structure can be created
74 by calling \Func{\_UPT\_create}(), passing the pid of the target process
75 as the only argument. The returned void-pointer then needs to be
76 passed as the ``argument'' pointer (third argument) to
77 \Func{unw\_init\_remote}().
79 The \Func{\_UPT\_resume}() routine can be used to resume execution of
80 the target process. It simply invokes \Func{ptrace}(2) with a command
81 value of \Const{PTRACE\_CONT}.
83 When the application is done using \Prog{libunwind} on the target
84 process, \Func{\_UPT\_destroy}() needs to be called, passing it the
85 void-pointer that was returned by the corresponding call to
86 \Func{\_UPT\_create}(). This ensures that all memory and other
87 resources are freed up.
89 \section{Availability}
91 Since \Func{ptrace}(2) works within a single machine only, the
92 \Prog{\_UPT}-facility by definition is not available in
93 \Prog{libunwind}-versions configured for cross-unwinding.
95 \section{Thread Safety}
97 The \Prog{\_UPT}-facility assumes that a single \Prog{\_UPT}-info
98 structure is never shared between threads. Because of this, no
99 explicit locking is used. As long as only one thread uses
100 a \Prog{\_UPT}-info structure at any given time, this facility
103 \section{Return Value}
105 \Func{\_UPT\_create}() may return a \Const{NULL} pointer if it fails
106 to create the \Prog{\_UPT}-info-structure for any reason. For the
107 current implementation, the only reason this call may fail is when the
108 system is out of memory.
113 \item[\File{libunwind-ptrace.h}] Headerfile to include when using the
114 interface defined by this library.
115 \item[\Opt{-l}\File{unwind-ptrace} \Opt{-l}\File{unwind-generic}]
116 Linker-switches to add when building a program that uses the
117 functions defined by this library.
123 \SeeAlso{libunwind(3)},
129 David Mosberger-Tang\\
130 Email: \Email{dmosberger@gmail.com}\\
131 WWW: \URL{http://www.nongnu.org/libunwind/}.