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126 lines
5.3 KiB
TeX
126 lines
5.3 KiB
TeX
\documentclass{article}
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\usepackage[fancyhdr,pdf]{latex2man}
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\input{common.tex}
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\begin{document}
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\begin{Name}{3}{libunwind-ptrace}{David Mosberger-Tang}{Programming Library}{ptrace() support in libunwind}libunwind-ptrace -- ptrace() support in libunwind
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\end{Name}
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\section{Synopsis}
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\File{\#include $<$libunwind.h$>$}\\
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\noindent
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\Type{unw\_accessors\_t} \Var{_UPT\_accessors};\\
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\Type{void~*}\Func{\_UPT\_create}(\Type{pid\_t});\\
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\noindent
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\Type{void} \Func{\_UPT\_destroy}(\Type{void~*});\\
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\noindent
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\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~*});\\
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\noindent
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\Type{void} \Func{\_UPT\_put\_unwind\_info}(\Type{unw\_addr\_space\_t}, \Type{unw\_proc\_info\_t~*}, \Type{void~*});\\
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\noindent
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\Type{int} \Func{\_UPT\_get\_dyn\_info\_list\_addr}(\Type{unw\_addr\_space\_t}, \Type{unw\_word\_t~*}, \Type{void~*});\\
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\noindent
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\Type{int} \Func{\_UPT\_access\_mem}(\Type{unw\_addr\_space\_t}, \Type{unw\_word\_t}, \Type{unw\_word\_t~*}, \Type{int}, \Type{void~*});\\
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\noindent
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\Type{int} \Func{\_UPT\_access\_reg}(\Type{unw\_addr\_space\_t}, \Type{unw\_regnum\_t}, \Type{unw\_word\_t~*}, \Type{int}, \Type{void~*});\\
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\noindent
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\Type{int} \Func{\_UPT\_access\_fpreg}(\Type{unw\_addr\_space\_t}, \Type{unw\_regnum\_t}, \Type{unw\_fpreg\_t~*}, \Type{int}, \Type{void~*});\\
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\noindent
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\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~*});\\
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\noindent
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\Type{int} \Func{\_UPT\_resume}(\Type{unw\_addr\_space\_t}, \Type{unw\_cursor\_t~*}, \Type{void~*});\\
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\section{Description}
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The \Func{ptrace}(2) system-call makes it possible for a process to
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gain access to the machine-state and virtual memory of \emph{another}
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process. With the right set of call-back routines, it is therefore
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possible to hook up \Prog{libunwind} to another process via
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\Func{ptrace}(2). While it's not very difficult to do so directly,
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\Prog{libunwind} further facilitates this task by providing
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ready-to-use callbacks for this purpose. The routines and variables
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implementing this facility use a name-prefix of \Func{\_UPT}, which is
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stands for ``unwind-via-ptrace''.
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An application that wants to use the \Func{\_UPT}-facility first needs
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to create a new \Prog{libunwind} address-space that represents the
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target process. This is done by calling
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\Func{unw\_create\_addr\_space}(). In many cases, the application
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will simply want to pass the address of \Var{\_UPT\_accessors} as the
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first argument to this routine. Doing so will ensure that
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\Prog{libunwind} will be able to properly unwind the target process.
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However, in special circumstances, an application may prefer to use
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only portions of the \Prog{\_UPT}-facility. For this reason, the
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individual callback routines (\Func{\_UPT\_find\_proc\_info}(),
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\Func{\_UPT\_put\_unwind\_info}(), etc.) are also available for direct
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use. Of course, the addresses of these routines could also be picked
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up from \Var{\_UPT\_accessors}, but doing so would prevent static
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initialization. Also, when using \Var{\_UPT\_accessors}, \emph{all}
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the callback routines will be linked into the application, even if
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they are never actually called.
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Next, the application can turn on ptrace-mode on the target process,
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either by forking a new process, invoking \Const{PTRACE\_TRACEME}, and
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then starting the target program (via \Func{execve}(2)), or by
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directly attaching to an already running process (via
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\Const{PTRACE\_ATTACH}). Either way, once the process-ID (pid) of the
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target process is known, a \Prog{\_UPT}-info-structure can be created
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by calling \Func{\_UPT\_create}(), passing the pid of the target process
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as the only argument. The returned void-pointer then needs to be
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passed as the ``argument'' pointer (third argument) to
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\Func{unw\_init\_remote}().
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The \Func{\_UPT\_resume}() routine can be used to resume execution of
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the target process. It simply invokes \Func{ptrace}(2) with a command
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value of \Const{PTRACE\_CONT}.
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When the application is done using \Prog{libunwind} on the target
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process, \Func{\_UPT\_destroy}() needs to be called, passing it the
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void-pointer that was returned by the corresponding call to
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\Func{\_UPT\_create}(). This ensures that all memory and other
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resources are freed up.
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\section{Availability}
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Since \Func{ptrace}(2) works within a single machine only, the
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\Prog{\_UPT}-facility by definition is not available in
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\Prog{libunwind}-versions configured for cross-unwinding.
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\section{Thread Safety}
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The \Prog{\_UPT}-facility assumes that a single \Prog{\_UPT}-info
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structure is never shared between threads. Because of this, no
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explicit locking is used. As long as only one thread uses
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a \Prog{\_UPT}-info structure at any given time, this facility
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is thread-safe.
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\section{Return Value}
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\Func{\_UPT\_create}() may return a \Const{NULL} pointer if it fails
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to create the \Prog{\_UPT}-info-structure for any reason. For the
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current implementation, the only reason this call may fail is when the
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system is out of memory.
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\section{See Also}
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execve(2),
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\SeeAlso{libunwind(3)},
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ptrace(2)
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\section{Author}
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\noindent
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David Mosberger-Tang\\
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Hewlett-Packard Labs\\
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Palo-Alto, CA 94304\\
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Email: \Email{davidm@hpl.hp.com}\\
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WWW: \URL{http://www.hpl.hp.com/research/linux/libunwind/}.
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\LatexManEnd
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\end{document}
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