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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}
The \Func{unw\_resume}() routine resumes execution at the stack frame
identified by \Var{cursor}. Normally, this is accomplished by
restoring the ``preserved'' (callee-saved) machine state. 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 the entire machine state, including
the ``preserved'' and ``scratch'' (caller-saved) registers, as well as
the signal mask.
identified by \Var{cursor}. The behavior of this routine differs
slightly for local and remote unwinding.
For local unwinding, \Func{unw\_resume}() restores the machine state
and then directly resumes execution in the target stack frame. Thus
\Func{unw\_resume}() does not return in this case. Restoring the
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
handlers (e.g., IA-64 uses \texttt{r15}-\texttt{r18} for this
purpose). These registers are normally treated like ``scratch''
registers. However, if \Prog{libunwind} is used to define an
exception argument register, e.g., by calling \Func{unw\_set\_reg}(),
then \Func{unw\_resume}() will always install the new value as the
contents of that register. In other words, the exception handling
arguments are installed even in cases where normally only the
registers. However, if \Prog{libunwind} is used to set an exception
argument register to a particular value (e.g., via
\Func{unw\_set\_reg}()), then \Func{unw\_resume}() will install this
value as the contents of the register. In other words, the exception
handling arguments are installed even in cases where normally only the
``preserved'' registers are restored.
Note that \Func{unw\_resume}() does \emph{not} invoke any unwind