---
name: "unw_set_reg"
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_set_reg"
---

# unw\_set\_reg(3)

## NAME

unw\_set\_reg -- set register contents

## SYNOPSIS

\#include \<libunwind.h\>\

int unw\_set\_reg(unw\_cursor\_t \*cp, unw\_regnum\_t reg, unw\_word\_t val);\

## DESCRIPTION

The unw\_set\_reg() routine sets the value of register  reg in the stack frame identified by cursor cp to the  value passed in val.

The register numbering is target dependent and described in separate  manual pages (e.g., libunwind-ia64(3libunwind) for the IA-64 target).  Furthermore, the exact set of accessible registers may depend on the  type of frame that cp is referring to. For ordinary stack  frames, it is normally possible to access only the preserved  (\`\`callee-saved'') registers and frame-related registers (such as the  stack pointer). However, for signal frames (see  unw\_is\_signal\_frame(3libunwind)), it is usually possible to access  all registers.

Note that unw\_set\_reg() can only write the contents of  registers whose values fit in a single word. See  unw\_set\_fpreg(3libunwind) for a way to write registers which do not  fit this constraint.

## RETURN VALUE

On successful completion, unw\_set\_reg() returns 0.  Otherwise the negative value of one of the error codes below is  returned.

## THREAD AND SIGNAL SAFETY

unw\_set\_reg() is thread-safe as well as safe to use  from a signal handler.

## ERRORS

- UNW\_EUNSPEC

   An unspecified error occurred.

- UNW\_EBADREG

   An attempt was made to write a register  that is either invalid or not accessible in the current frame.

- UNW\_EREADONLY

   An attempt was made to write to a  read-only register.

In addition, unw\_set\_reg() may return any error returned by  the access\_mem(), access\_reg(), and  access\_fpreg() callbacks (see  unw\_create\_addr\_space(3libunwind)).

## SEE ALSO

libunwind(3libunwind), libunwind-ia64(3libunwind), unw\_get\_reg(3libunwind), unw\_is\_signal\_frame(3libunwind), unw\_set\_fpreg(3libunwind)

## AUTHOR

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