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unw_set_reg(3) [debian man page]

UNW_SET_REG(3)						       Programming Library						    UNW_SET_REG(3)

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(3) for the IA-64 target). Further- more, the exact set of accessible registers may depend on the type of frame that cp is referring to. For ordinary stack frames, it is nor- mally 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(3)), 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(3) 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() call-backs (see unw_cre- ate_addr_space(3)). SEE ALSO
libunwind(3), libunwind-ia64(3), unw_get_reg(3), unw_is_signal_frame(3), unw_set_fpreg(3) AUTHOR
David Mosberger-Tang Email: WWW: Programming Library 16 August 2007 UNW_SET_REG(3)

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UNW_RESUME(3)						       Programming Library						     UNW_RESUME(3)

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) regis- ters. However, if execution in any of the stack frames younger (more deeply nested) than the one identified by cp was interrupted by a sig- nal, 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 han- dling 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 (applica- tion-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(3), unw_set_reg(3), sigprocmask(2) AUTHOR
David Mosberger-Tang Email: WWW: Programming Library 16 August 2007 UNW_RESUME(3)

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