sysi86(S)

sysi86 -- machine-specific functions

Synopsis

   #include <sys/sysi86.h>
   
   int sysi86(int cmd, . . .);

Description

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.

Command SI86FPHW

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.

FP_NO no fp chip, no emulator (no fp support)

FP_SW no fp chip, using software emulator

FP_HW chip present bit

FP_287 80287 chip present

FP_387 80387 chip present

Command STIME

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.

Command SI86DSCR

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.

Command SI86IOPL

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 command.

The argument is an integer which is the new I/O privilege level (0-3).

Command SI86NULLPTR

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 parameter.

When null-pointer dereferences are enabled, any user program attempt to read memory in the first page (addresses 0-4095) will successfully return zero. 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.

Return values

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.

Errors

When the cmd is invalid, errno is set to EINVAL.

References

nullptr(C), swap(ADM), uname(S)

	FP_NO	no fp chip, no emulator (no fp support)
	FP_SW	no fp chip, using software emulator
	FP_HW	chip present bit
	FP_287	80287 chip present
	FP_387	80387 chip present