__far_jump() — perform far jump (C/C++ and XPLINK only)

The __far_jump() interface performs a function similar to longjmp(). However, it does not require a setjmp() to be performed previously. The information required to perform this "nonlocal goto" is provided by the user in the __jumpinfo structure. This information is normally provided in a jmp_buf and saved by the library when a setjmp() is invoked, When used in conjunction with __set_stack_softlimit(), described in __set_stack_softlimit() — set stack soft limit (C/C++ and XPLINK only), the information needed to fill in __jumpinfo can be obtained from data passed to a signal handler set up to field a softlimit stack overflow signal. This information includes registers, psw, and signal mask.

struct __jumpinfo * JumpInfo

The __jumpinfo structure must be cleared before it is filled in to ensure that all reserved areas are zero. The __jumpinfo structure appears in the following format:

struct __jumpinfo
{
  char              __ji_u1[68];
  char              __ji_mask_saved;
  char              __ji_u2[3];
  sigset_t          __ji_sigmask;
  char              __ji_u3[11];
  unsigned          __ji_fl_fp4       :1;
  unsigned          __ji_fl_fp16      :1;
  unsigned          __ji_fl_fpc       :1;
  unsigned          __ji_fl_res1a     :1;
  unsigned          __ji_fl_hr        :1;
  unsigned          __ji_fl_res2      :1;
  unsigned          __ji_fl_exp       :1;
  unsigned          __ji_fl_res2a     :1;
 
  char __ji_u4[12];
  struct __jumpinfo_vr_ext *__ji_vr_ext;
#ifndef _LP64
  char __ji_u7[4]; //only available in AMode 31
#endif
  char __ji_u8[16];
  long              __ji_gr[16];
  long              __ji_hr[16];
  int               __ji_u5[16];
  double            __ji_fpr[16];
  int               __ji_fpc;

__ji_gr

Contains the following:

• The values of the 16 general purpose registers that are restored
• The value in Register 7 will be used as the target address of the jump
• The value of Register 4 will be used as the target DSA address

__ji_hr

Contains the values of the high halves of the 16 general purpose registers (0-15) that are restored. This is valid only on 64 bit hardware when running in 31 bit mode.

__ji_fpr

Contains the values of either 4 or 16 floating-point registers. If all 16 floating-point registers are present, registers 0-15 are saved in __ji_fpr[0] through __ji_fpr[15]. If only 4 floating-point registers are present, they are registers 0, 2, 4, and 6; these are saved in __ji_fpr[0], __ji_fpr[2], __ji_fpr[4], and __ji_fpr[6].

__ji_mask_saved

Indicator field that is set to non-zero value when the signal mask field (__ji_sigmask) is valid.

__ji_sigmask

Contains the signal mask value.

__ji_fpc

Contains the floating point control register value.

__ji_fl_fp4

Set to one when values for the 4 floating-point registers 0, 2, 4, and 6 are provided in __ji_fpr. This bit should also be set to one whenever all floating-point registers 0-15 are present (when __ji_fl_fp16 is also set to one.)

__ji_fl_fp16

Set to one when values for all 16 floating-point registers 0-15 are provided in __ji_fpr. In this case, __ji_fl_fp4 should also be set to one.

__ji_fl_fpc

Set to one when the value of the floating-point control register is provided in __ji_fpc.

__ji_fl_exp

Set to one when explicit backchaining is complete to the target stack.

__ji_fl_hr

Set to one when values for the high halves of general registers 0-15 are provided in __ji_hr. This flag is set only in 31-bit addressing mode. In 64-bit addressing mode, __ji_gr contains 64-bit values for the general registers, and __ji_fl_hr is not set.

__ji_vr_ext

When the Vector Registers are available on the target machine, the __ji_vr_ext field can be set to a pointer to vector register save area or set to NULL if vector registers are not to be restored.

typedef char __jumpinfo_vector_t[16];
struct __jumpinfo_vr_ext
{
   short __ji_ve_version;
   char __ji_ve_u[14];
   __jumpinfo_vector_t__ji_ve_savearea[32];
}

__ji_ve_version

Always set to zero.

__ji_ve_u

Reserved bytes and should always set to all zero.

__ji_ve_savearea

Contains the values of 32 Vector Registers (16 bytes each).

The __far_jump() function has no returned value. When __far_jump() completes, program execution continues at the target address.