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Describe behavior difference between local and remote unw_resume().

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hp.com!davidm 2003-02-22 03:08:22 +00:00
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doc/unw_resume.tex
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@ -19,22 +19,34 @@
\section{Description} \section{Description}
The \Func{unw\_resume}() routine resumes execution at the stack frame The \Func{unw\_resume}() routine resumes execution at the stack frame
identified by \Var{cursor}. Normally, this is accomplished by identified by \Var{cursor}. The behavior of this routine differs
restoring the ``preserved'' (callee-saved) machine state. However, if slightly for local and remote unwinding.
execution in any of the stack frames younger (more deeply nested) than
the one identified by \Var{cursor} was interrupted by a signal, then For local unwinding, \Func{unw\_resume}() restores the machine state
\Func{unw\_resume}() will restore the entire machine state, including and then directly resumes execution in the target stack frame. Thus
the ``preserved'' and ``scratch'' (caller-saved) registers, as well as \Func{unw\_resume}() does not return in this case. Restoring the
the signal mask. machine state normally involves restoring the ``preserved''
(callee-saved) registers. However, if execution in any of the stack
frames younger (more deeply nested) than the one identified by
\Var{cursor} was interrupted by a signal, then \Func{unw\_resume}()
will restore all registers as well as the signal mask.
For remote unwinding, \Func{unw\_resume}() installs the machine state
identified by the cursor by calling the \Func{access\_reg} and
\Func{access\_fpreg} accessor callbacks as needed. Once that is
accomplished, the \Func{resume} accessor callback is invoked. The
\Func{unw\_resume} routine then returns normally (that is, unlikely
for local unwinding, \Func{unw\_resume} will always return for remote
unwinding).
Most platforms reserve some registers to pass arguments to exception Most platforms reserve some registers to pass arguments to exception
handlers (e.g., IA-64 uses \texttt{r15}-\texttt{r18} for this handlers (e.g., IA-64 uses \texttt{r15}-\texttt{r18} for this
purpose). These registers are normally treated like ``scratch'' purpose). These registers are normally treated like ``scratch''
registers. However, if \Prog{libunwind} is used to define an registers. However, if \Prog{libunwind} is used to set an exception
exception argument register, e.g., by calling \Func{unw\_set\_reg}(), argument register to a particular value (e.g., via
then \Func{unw\_resume}() will always install the new value as the \Func{unw\_set\_reg}()), then \Func{unw\_resume}() will install this
contents of that register. In other words, the exception handling value as the contents of the register. In other words, the exception
arguments are installed even in cases where normally only the handling arguments are installed even in cases where normally only the
``preserved'' registers are restored. ``preserved'' registers are restored.
Note that \Func{unw\_resume}() does \emph{not} invoke any unwind Note that \Func{unw\_resume}() does \emph{not} invoke any unwind