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       getunwind - copy the unwind data to caller's buffer


       Standard C library (libc, -lc)


       #include <linux/unwind.h>
       #include <sys/syscall.h>      /* Definition of SYS_* constants */
       #include <unistd.h>

       [[deprecated]] long syscall(SYS_getunwind, void buf[.buf_size],
                                   size_t buf_size);


       Note: this system call is obsolete.

       The IA-64-specific getunwind() system call copies the kernel's call frame unwind data into
       the buffer pointed to by buf and returns the size of the unwind data; this data  describes
       the gate page (kernel code that is mapped into user space).

       The  size of the buffer buf is specified in buf_size.  The data is copied only if buf_size
       is greater than or equal to the size of the unwind data and 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.

       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:

           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)

       An entry whose start value is zero indicates the end of the table.  For  more  information
       about the format, see the IA-64 Software Conventions and Runtime Architecture manual.


       On success, getunwind() returns the size of the unwind data.  On error, -1 is returned and
       errno is set to indicate the error.


       getunwind() fails with the error EFAULT if the unwind info can't be stored  in  the  space
       specified by buf.


       This system call is available since Linux 2.4.


       This system call is Linux-specific, and is available only on the IA-64 architecture.


       This  system  call has been deprecated.  The modern way to obtain the kernel's unwind data
       is via the vdso(7).