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# getunwind() - Unix, Linux System Call

# NAME

getunwind - copy the unwind data to caller’s buffer

# SYNOPSIS

    #include <syscall.h>
    #include <linux/unwind.h>

    long getunwind (void *buf, size_t buf_size);

# DESCRIPTION

The sys_getunwind function returns size of unwind table, which describes gate page (kernel code that is mapped into user space).

The unwind data is copied to the buffer buf, which has size 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. The system call returns the size of the unwind data in both cases.

The first part of the unwind data contains an unwind table. The rest contains the associated unwind info in random order. The unwind table contains a table looking like:

            u64 start;      (64-bit address of start of function)
            u64 end;        (64-bit address of start of function)
            u64 info;       (BUF-relative offset to unwind info)

An entry with a START address of zero is the end of table. For more information about the format you can see the IA-64 Software Conventions and Runtime Architecture.

# RETURN VALUE

The sys_getunwind function returns size of unwind table.

# ERRORS

The sys_getunwind function fails with EFAULT if the unwind info can’t be stored in the space specified by the buf argument.

# AVAILABILITY

This system call is available only on the IA-64 architecture.

# APPLICATION USAGE

This system call has been deprecated. It’s highly recommended to get at the kernel’s unwind info by the gate DSO. The address of the ELF header for this DSO is passed to user level via AT_SYSINFO_EHDR.

The system call is not available to application programs as a function; it can be called using the syscall(2) function.

# SEE ALSO

- syscall (2)

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