The sysi86 system call implements machine-specific functions.
The cmd argument determines the function to be performed.
The types of the arguments expected depend on the function.
This command expects the address of an integer as its argument.
After successful return from the system call,
the integer specifies how floating-point computation is supported.
The low-order byte of the integer contains the value of ``fpkind,''
a variable that specifies whether an 80287 or 80387 floating-point
coprocessor is present, emulated in software, or not supported.
The values are defined in the header file sys/fp.h.
no fp chip, no emulator (no fp support)
no fp chip, using software emulator
chip present bit
80287 chip present
80387 chip present
When cmd is STIME, an argument of type long is expected.
This function sets the system time and date (not the hardware clock).
The argument contains the time as measured
in seconds from 00:00:00 GMT January 1, 1970.
The calling process must have the P_SYSOPS privilege to
use this command.
This command sets a segment descriptor in the kernel.
It accepts as a descriptor
executable and data segments in the LDT at DPL 3.
The argument is a pointer to a request structure
that contains the values to be placed in the descriptor.
The request structure is declared in the sys/sysi86.h header file.
This command changes the I/O privilege level for the invoking LWP.
Setting the IOPL to 3 allows the lightweight process (LWP) to directly
perform input/output instructions to access all hardware device ports.
The calling process must have the P_SYSOPS privilege to use this
The argument is an integer which is the new I/O privilege level (0-3).
This command controls the system behavior when applications
dereference through a NULL pointer.
To support existing applications the default behavior as delivered is
to enable null-pointer dereferences.
The default behavior can be changed by changing the nullptr to enable
When null-pointer dereferences are enabled, any user program attempt
to read memory in the first page (addresses 0-4095) will successfully
When disabled, these memory reads behave like any other bad memory
reference and cause a SIGSEGV signal to be sent to the referencing LWP.
Memory writes to page 0 always generate SIGSEGV.
The argument for SI86NULLPTR is an integer.
A value of zero disables null-pointer dereferences for the current user ID.
A value of one enables null-pointer dereferences for the current user ID.
A value of two returns the current setting.
If sysi86 succeeds, it returns zero or a value that
depends on cmd as described above.
If sysi86 fails, it returns -1 and sets errno
to identify the error.