1 \documentclass{article} 2 \usepackage[fancyhdr,pdf]{latex2man} 3 4 \input{common.tex} 5 6 \begin{document} 7 8 \begin{Name}{3}{libunwind-ptrace}{David Mosberger-Tang}{Programming Library}{ptrace() support in libunwind}libunwind-ptrace -- ptrace() support in libunwind 9 \end{Name} 10 11 \section{Synopsis} 12 13 \File{\#include $<$libunwind-ptrace.h$>$}\\ 14 15 \noindent 16 \Type{unw\_accessors\_t} \Var{\_UPT\_accessors};\\ 17 18 \Type{void~*}\Func{\_UPT\_create}(\Type{pid\_t});\\ 19 \noindent 20 \Type{void} \Func{\_UPT\_destroy}(\Type{void~*});\\ 21 22 \noindent 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~*});\\ 24 \noindent 25 \Type{void} \Func{\_UPT\_put\_unwind\_info}(\Type{unw\_addr\_space\_t}, \Type{unw\_proc\_info\_t~*}, \Type{void~*});\\ 26 \noindent 27 \Type{int} \Func{\_UPT\_get\_dyn\_info\_list\_addr}(\Type{unw\_addr\_space\_t}, \Type{unw\_word\_t~*}, \Type{void~*});\\ 28 \noindent 29 \Type{int} \Func{\_UPT\_access\_mem}(\Type{unw\_addr\_space\_t}, \Type{unw\_word\_t}, \Type{unw\_word\_t~*}, \Type{int}, \Type{void~*});\\ 30 \noindent 31 \Type{int} \Func{\_UPT\_access\_reg}(\Type{unw\_addr\_space\_t}, \Type{unw\_regnum\_t}, \Type{unw\_word\_t~*}, \Type{int}, \Type{void~*});\\ 32 \noindent 33 \Type{int} \Func{\_UPT\_access\_fpreg}(\Type{unw\_addr\_space\_t}, \Type{unw\_regnum\_t}, \Type{unw\_fpreg\_t~*}, \Type{int}, \Type{void~*});\\ 34 \noindent 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~*});\\ 36 \noindent 37 \Type{int} \Func{\_UPT\_resume}(\Type{unw\_addr\_space\_t}, \Type{unw\_cursor\_t~*}, \Type{void~*});\\ 38 39 \section{Description} 40 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''. 50 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. 67 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}(). 78 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}. 82 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. 88 89 \section{Availability} 90 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. 94 95 \section{Thread Safety} 96 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 101 is thread-safe. 102 103 \section{Return Value} 104 105 \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. 109 110 \section{Files} 111 112 \begin{Description} 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. 118 \end{Description} 119 120 \section{See Also} 121 122 execve(2), 123 \SeeAlso{libunwind(3)}, 124 ptrace(2) 125 126 \section{Author} 127 128 \noindent 129 David Mosberger-Tang\\ 130 Email: \Email{dmosberger (a] gmail.com}\\ 131 WWW: \URL{http://www.nongnu.org/libunwind/}. 132 \LatexManEnd 133 134 \end{document} 135
