DragonFly On-Line Manual Pages
UNW_RESUME(3) Programming Library UNW_RESUME(3)
unw_resume -- resume execution in a particular stack frame
int unw_resume(unw_cursor_t *cp);
The unw_resume() routine resumes execution at the stack frame
identified 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
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 cp was interrupted by a signal, then
unw_resume() will restore all registers as well as the signal mask.
Attempting 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
identified 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 remote 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
``preserved'' registers are restored.
Note that unw_resume() does not invoke any unwind handlers (aka,
``personality 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 appropriately 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
For local unwinding, unw_resume() does not return on success. For
remote 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
address-space, this routine is also safe to use from a signal handler.
An unspecified error occurred.
A register needed by unw_resume() wasn't accessible.
The instruction pointer identified by cp is not valid.
The stack frame identified by cp is not valid.
libunwind(3), unw_set_reg(3), sigprocmask(2)
Programming Library 16 August 2007 UNW_RESUME(3)