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UNW_RESUME(3libunwind) Programming Library UNW_RESUME(3libunwind) 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(3libunwind), unw_set_reg(3libunwind), sigprocmask(2) AUTHOR David Mosberger-Tang Email: dmosberger@gmail.com WWW: http://www.nongnu.org/libunwind/. Programming Library 29 August 2023 UNW_RESUME(3libunwind)
NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | THREAD AND SIGNAL SAFETY | ERRORS | SEE ALSO | AUTHOR
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