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.TH getunwind 2 2023-10-31 "Linux man-pages 6.7"
.SH NAME
getunwind \- copy the unwind data to caller's buffer
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.B #include <linux/unwind.h>
.BR "#include <sys/syscall.h>" "      /* Definition of " SYS_* " constants */"
.B #include <unistd.h>
.P
.BI "[[deprecated]] long syscall(SYS_getunwind, void " buf [. buf_size ],
.BI "                            size_t " buf_size );
.fi
.SH DESCRIPTION
.I Note: this system call is obsolete.
.P
The
IA-64-specific
.BR getunwind ()
system call copies the kernel's call frame
unwind data into the buffer pointed to by
.I buf
and returns the size of the unwind data;
this data describes the gate page (kernel code that
is mapped into user space).
.P
The size of the buffer
.I buf
is specified in
.IR buf_size .
The data is copied only if
.I buf_size
is greater than or equal to the size of the unwind data and
.I buf
is not NULL;
otherwise, no data is copied, and the call succeeds,
returning the size that would be needed to store the unwind data.
.P
The first part of the unwind data contains an unwind table.
The rest contains the associated unwind information, in no particular order.
The unwind table contains entries of the following form:
.P
.in +4n
.EX
u64 start;      (64\-bit address of start of function)
u64 end;        (64\-bit address of end of function)
u64 info;       (BUF\-relative offset to unwind info)
.EE
.in
.P
An entry whose
.I start
value is zero indicates the end of the table.
For more information about the format, see the
.I IA-64 Software Conventions and Runtime Architecture
manual.
.SH RETURN VALUE
On success,
.BR getunwind ()
returns the size of the unwind data.
On error, \-1 is returned and
.I errno
is set to indicate the error.
.SH ERRORS
.BR getunwind ()
fails with the error
.B EFAULT
if the unwind info can't be stored in the space specified by
.IR buf .
.SH STANDARDS
Linux on IA-64.
.SH HISTORY
Linux 2.4.
.P
This system call has been deprecated.
The modern way to obtain the kernel's unwind data is via the
.BR vdso (7).
.SH SEE ALSO
.BR getauxval (3)