---
name: "unw_resume"
section: "3"
platform: "linux"
package: "libunwind"
version: "1.8.3-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/unw_resume"
---

# 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  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 (application-binary interface).

## RETURN VALUE

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.

## 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)](/sigprocmask/2.md)

## AUTHOR

David Mosberger-Tang\
 Email: **dmosberger@gmail.com**\
 WWW: **http://www.nongnu.org/libunwind/**.