Wire up sys_execveat(). This passes the selftests for the system call.

Check success of execveat(3, '../execveat', 0)... [OK]
Check success of execveat(5, 'execveat', 0)... [OK]
Check success of execveat(6, 'execveat', 0)... [OK]
Check success of execveat(-100, '/home/pranith/linux/...ftests/exec/execveat', 0)... [OK]
Check success of execveat(99, '/home/pranith/linux/...ftests/exec/execveat', 0)... [OK]
Check success of execveat(8, '', 4096)... [OK]
Check success of execveat(17, '', 4096)... [OK]
Check success of execveat(9, '', 4096)... [OK]
Check success of execveat(14, '', 4096)... [OK]
Check success of execveat(14, '', 4096)... [OK]
Check success of execveat(15, '', 4096)... [OK]
Check failure of execveat(8, '', 0) with ENOENT... [OK]
Check failure of execveat(8, '(null)', 4096) with EFAULT... [OK]
Check success of execveat(5, 'execveat.symlink', 0)... [OK]
Check success of execveat(6, 'execveat.symlink', 0)... [OK]
Check success of execveat(-100, '/home/pranith/linux/...xec/execveat.symlink', 0)... [OK]
Check success of execveat(10, '', 4096)... [OK]
Check success of execveat(10, '', 4352)... [OK]
Check failure of execveat(5, 'execveat.symlink', 256) with ELOOP... [OK]
Check failure of execveat(6, 'execveat.symlink', 256) with ELOOP... [OK]
Check failure of execveat(-100, '/home/pranith/linux/tools/testing/selftests/exec/execveat.symlink', 256) with ELOOP... [OK]
Check success of execveat(3, '../script', 0)... [OK]
Check success of execveat(5, 'script', 0)... [OK]
Check success of execveat(6, 'script', 0)... [OK]
Check success of execveat(-100, '/home/pranith/linux/...elftests/exec/script', 0)... [OK]
Check success of execveat(13, '', 4096)... [OK]
Check success of execveat(13, '', 4352)... [OK]
Check failure of execveat(18, '', 4096) with ENOENT... [OK]
Check failure of execveat(7, 'script', 0) with ENOENT... [OK]
Check success of execveat(16, '', 4096)... [OK]
Check success of execveat(16, '', 4096)... [OK]
Check success of execveat(4, '../script', 0)... [OK]
Check success of execveat(4, 'script', 0)... [OK]
Check success of execveat(4, '../script', 0)... [OK]
Check failure of execveat(4, 'script', 0) with ENOENT... [OK]
Check failure of execveat(5, 'execveat', 65535) with EINVAL... [OK]
Check failure of execveat(5, 'no-such-file', 0) with ENOENT... [OK]
Check failure of execveat(6, 'no-such-file', 0) with ENOENT... [OK]
Check failure of execveat(-100, 'no-such-file', 0) with ENOENT... [OK]
Check failure of execveat(5, '', 4096) with EACCES... [OK]
Check failure of execveat(5, 'Makefile', 0) with EACCES... [OK]
Check failure of execveat(11, '', 4096) with EACCES... [OK]
Check failure of execveat(12, '', 4096) with EACCES... [OK]
Check failure of execveat(99, '', 4096) with EBADF... [OK]
Check failure of execveat(99, 'execveat', 0) with EBADF... [OK]
Check failure of execveat(8, 'execveat', 0) with ENOTDIR... [OK]
Invoke copy of 'execveat' via filename of length 4093:
Check success of execveat(19, '', 4096)... [OK]
Check success of execveat(5, 'xxxxxxxxxxxxxxxxxxxx...yyyyyyyyyyyyyyyyyyyy', 0)... [OK]
Invoke copy of 'script' via filename of length 4093:
Check success of execveat(20, '', 4096)... [OK]
/bin/sh: 0: Can't open /dev/fd/5/xxxxxxx(... a long line of x's and y's, 0)... [OK]
Check success of execveat(5, 'xxxxxxxxxxxxxxxxxxxx...yyyyyyyyyyyyyyyyyyyy', 0)... [OK]

Tested on a 32-bit powerpc system.
Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>