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