1\documentclass{article} 2\usepackage[fancyhdr,pdf]{latex2man} 3 4\input{common.tex} 5 6\begin{document} 7 8\begin{Name}{3}{unw\_resume}{David Mosberger-Tang}{Programming Library}{unw\_resume}unw\_resume -- resume execution in a particular stack frame 9\end{Name} 10 11\section{Synopsis} 12 13\File{\#include $<$libunwind.h$>$}\\ 14 15\Type{int} \Func{unw\_resume}(\Type{unw\_cursor\_t~*}\Var{cp});\\ 16 17\section{Description} 18 19The \Func{unw\_resume}() routine resumes execution at the stack frame 20identified by \Var{cp}. The behavior of this routine differs 21slightly for local and remote unwinding. 22 23For local unwinding, \Func{unw\_resume}() restores the machine state 24and then directly resumes execution in the target stack frame. Thus 25\Func{unw\_resume}() does not return in this case. Restoring the 26machine state normally involves restoring the ``preserved'' 27(callee-saved) registers. However, if execution in any of the stack 28frames younger (more deeply nested) than the one identified by 29\Var{cp} was interrupted by a signal, then \Func{unw\_resume}() will 30restore all registers as well as the signal mask. Attempting to call 31\Func{unw\_resume}() on a cursor which identifies the stack frame of 32another thread results in undefined behavior (e.g., the program may 33crash). 34 35For remote unwinding, \Func{unw\_resume}() installs the machine state 36identified by the cursor by calling the \Func{access\_reg} and 37\Func{access\_fpreg} accessor callbacks as needed. Once that is 38accomplished, the \Func{resume} accessor callback is invoked. The 39\Func{unw\_resume} routine then returns normally (that is, unlikely 40for local unwinding, \Func{unw\_resume} will always return for remote 41unwinding). 42 43Most platforms reserve some registers to pass arguments to exception 44handlers (e.g., IA-64 uses \texttt{r15}-\texttt{r18} for this 45purpose). These registers are normally treated like ``scratch'' 46registers. However, if \Prog{libunwind} is used to set an exception 47argument register to a particular value (e.g., via 48\Func{unw\_set\_reg}()), then \Func{unw\_resume}() will install this 49value as the contents of the register. In other words, the exception 50handling arguments are installed even in cases where normally only the 51``preserved'' registers are restored. 52 53Note that \Func{unw\_resume}() does \emph{not} invoke any unwind 54handlers (aka, ``personality routines''). If a program needs this, it 55will have to do so on its own by obtaining the \Type{unw\_proc\_info\_t} 56of each unwound frame and appropriately processing its unwind handler 57and language-specific data area (lsda). These steps are generally 58dependent on the target-platform and are regulated by the 59processor-specific ABI (application-binary interface). 60 61\section{Return Value} 62 63For local unwinding, \Func{unw\_resume}() does not return on success. 64For remote unwinding, it returns 0 on success. On failure, the 65negative value of one of the errors below is returned. 66 67\section{Thread and Signal Safety} 68 69\Func{unw\_resume}() is thread-safe. If cursor \Var{cp} is in the 70local address-space, this routine is also safe to use from a signal 71handler. 72 73\section{Errors} 74 75\begin{Description} 76\item[\Const{UNW\_EUNSPEC}] An unspecified error occurred. 77\item[\Const{UNW\_EBADREG}] A register needed by \Func{unw\_resume}() wasn't 78 accessible. 79\item[\Const{UNW\_EINVALIDIP}] The instruction pointer identified by 80 \Var{cp} is not valid. 81\item[\Const{UNW\_BADFRAME}] The stack frame identified by 82 \Var{cp} is not valid. 83\end{Description} 84 85\section{See Also} 86 87\SeeAlso{libunwind(3)}, 88\SeeAlso{unw\_set\_reg(3)}, 89sigprocmask(2) 90 91\section{Author} 92 93\noindent 94David Mosberger-Tang\\ 95Email: \Email{dmosberger@gmail.com}\\ 96WWW: \URL{http://www.nongnu.org/libunwind/}. 97\LatexManEnd 98 99\end{document} 100