UNW_RESUME(3) Programming Library UNW_RESUME(3)
NAME
unw_resume -- resume execution in a particular stack frame
SYNOPSIS
#include <libunwind.h>
int unw_resume(unw_cursor_t *cp);
DESCRIPTION
The unw_resume() routine resumes execution at the stack frame identi-
fied by cp. The behavior of this routine differs slightly for local
and remote unwinding.
For local unwinding, unw_resume() restores the machine state and then
directly resumes execution in the target stack frame. Thus unw_resume()
does not return in this case. Restoring the machine state normally in-
volves restoring the ``preserved'' (callee-saved) registers. However,
if execution in any of the stack frames younger (more deeply nested)
than the one identified by cp was interrupted by a signal, then unw_re-
sume() will restore all registers as well as the signal mask. Attempt-
ing to call unw_resume() on a cursor which identifies the stack frame
of another thread results in undefined behavior (e.g., the program may
crash).
For remote unwinding, unw_resume() installs the machine state identi-
fied by the cursor by calling the access_reg and access_fpreg accessor
callbacks as needed. Once that is accomplished, the resume accessor
callback is invoked. The unw_resume routine then returns normally (that
is, unlikely for local unwinding, unw_resume will always return for re-
mote unwinding).
Most platforms reserve some registers to pass arguments to exception
handlers (e.g., IA-64 uses r15-r18 for this purpose). These registers
are normally treated like ``scratch'' registers. However, if libunwind
is used to set an exception argument register to a particular value
(e.g., via unw_set_reg()), then 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 ``pre-
served'' registers are restored.
Note that unw_resume() does not invoke any unwind handlers (aka, ``per-
sonality routines''). If a program needs this, it will have to do so on
its own by obtaining the unw_proc_info_t of each unwound frame and ap-
propriately processing its unwind handler and language-specific data
area (lsda). These steps are generally dependent on the target-platform
and are regulated by the processor-specific ABI (application-binary in-
terface).
RETURN VALUE
For local unwinding, unw_resume() does not return on success. For re-
mote unwinding, it returns 0 on success. On failure, the negative value
of one of the errors below is returned.
THREAD AND SIGNAL SAFETY
unw_resume() is thread-safe. If cursor cp is in the local ad-
dress-space, this routine is also safe to use from a signal handler.
ERRORS
UNW_EUNSPEC
An unspecified error occurred.
UNW_EBADREG
A register needed by unw_resume() wasn't accessible.
UNW_EINVALIDIP
The instruction pointer identified by cp is not valid.
UNW_BADFRAME
The stack frame identified by cp is not valid.
SEE ALSO
libunwind(3), unw_set_reg(3), sigprocmask(2)
AUTHOR
David Mosberger-Tang
Email: dmosberger@gmail.com
WWW: http://www.nongnu.org/libunwind/.
Programming Library 16 August 2007 UNW_RESUME(3)
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