NAME
aout — kernel support for executing binary files in legacy a.out formatSYNOPSIS
kldload a.out
DESCRIPTION
The a.out(5) executable format was used before the release of FreeBSD 3.0. Since i386 was the only supported architecture at that time, a.out(5) executables can only be activated on platforms that support execution of i386 code, such as i386 and amd64. To add kernel support for old syscalls and old syscall invocation methods, place the following options in the kernel configuration file:
options
COMPAT_43
options COMPAT_FREEBSD32
The COMPAT_FREEBSD32 option is only required on
64-bit CPU architectures.
The aout.ko module needs to be loaded with the
kldload(8) utility in order to support the
a.out(5) image activator:
kldload
aout
Alternatively, to load the module at boot time, place the following line in
loader.conf(5):
aout_load="YES"
- security.bsd.map_at_zero
- Set to 1 to allow mapping of process pages at address 0. Some very old ZMAGIC executable images require text mapping at address 0.
- kern.pid_max
- Old versions of FreeBSD used signed 16-bit type for pid_t. Current kernels use 32-bit type for pid_t, and allow process id's up to 99999. Such values cannot be represented by old pid_t, mostly causing issues for processes using wait(2) syscalls, for example shells. Set the sysctl to 30000 to work around the problem.
- kern.elf32.read_exec
- Set to 1 to force any accessible memory mapping performed by 32-bit process to allow execution, see mmap(2). Old i386 CPUs did not have a bit in PTE which disallowed execution from the page, so many old programs did not specify PROT_EXEC even for mapping of executable code. The sysctl forces PROT_EXEC if mapping has any access allowed at all. The setting is only needed if the host architecture allows non-executable mappings.
SEE ALSO
execve(2), a.out(5), elf(5), sysctl(8)HISTORY
The a.out(5) executable format was used on ancient AT&T UNIX and served as the main executable format for FreeBSD from the beginning up to FreeBSD 2.2.9. In FreeBSD 3.0 it was superseded by elf(5).AUTHORS
The aout manual page was written by Konstantin Belousov <[email protected]>.BUGS
On 64bit architectures, not all wrappers for older syscalls are implemented.| August 14, 2012 | Debian |