HP-UX Reference (11i v2 04/09) - 3 Library Functions A-M (vol 6)

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_UNW_currentContext(3X) _UNW_currentContext(3X)

(Itanium(R)-based Systems Only)

values in the _Unwind_Context

of General Registers 1-31, scratch and preserved Floating Point

Registers, scratch and preserved Predicate Registers, Branch Registers 0-7, IP, CFM, and Application

Registers in the set RSC, BSP, BSPSTORE, RNAT, CCV, UNAT, FPSR, ITC, PFS, LC. Writing to a

particular register validates that value in the

_Unwind_Context

. A call to

_UNW_setCFM invali-

dates the

_Unwind_Context

’s general register values in the range GR32..GR127 and validates the

_Unwind_Context

’s current frame marker (CFM) value. Once the CFM value is valid writes to Gen-

eral Registers in the range, GR32 through GR32 + CFM.sof are allowed (for the purpose of initializing

RSE stacked general registers in the current procedure’s RSE frame).

A speciﬁc set of registers listed in the unwind(5) INITIALIZATION section must be validated in order for

a call to

_UNW_step() to be successful.

Any initialization of register values not speciﬁcally listed in the previous paragraph is not allowed. For

instance initialization of the constant registers (GR0, FR0, FR1, PR0) are not allowed. Violating this

rule results in the the

_Unwind_Context

alert code set to

_UNW_INITIALIZATION_RANGE_ERROR

and the _UNW_set... function returning

_UNW_INITIALIZATION_RANGE_ERROR

Attempts to initialize an

_Unwind_Context

object which is in a state where initialization of values is

not allowed causes no change to the value in

_Unwind_Context

. It results in a return alert code of

_UNW_SET_NOT_ALLOWED_IN_STATE

. See also unwind(5).

The unwind library register value initializer functions refer to registers by their physical numbers as

opposed to the mapped (logical) numbers associated with rotations indicated in CFM.sor, CFM.rrb.gr,

CFM.rrb.pr, CFM.rrb.fr . The stack unwind library deﬁnes the physical number to be the register

number the value would lie in should the appropriate CFM.rrb ﬁeld have value 0.

The mapping functions

_UNW_GR_PhysicalNumber

, _UNW_FR_PhysicalNumber, and

_UNW_PR_PhysicalNumber

return the physical register number to pass to the _UNW_get... ini-

tializer functions to access a given logical register. Passing a mapping function a logical number which is

outside of the range of mapped logical numbers returns 0 and sets the

_UNW_QUERY_RANGE_ERROR

alert condition. For example, calling _UNW_GR_PhysicalNumber(uc,42)

while CFM.sor is 0 sets

the alert condition. The contents of the

_Unwind_Context

object’s CFM should be initialized prior to

using the mapping functions.

_UNW_step modiﬁes the _Unwind_Context

pointed to by parameter p to represent the predecessor’s

processor state.

RETURN VALUE

_UNW_set... returns _UNW_SET_NOT_ALLOWED_IN_STATE

when _Unwind_Context is in a

state where initialization of values is not allowed. States in which initialization is allowed are Init and

Pre_Install. See Error conditions and recovery on the manual page unwind(5).

_UNW_set... returns _UNW_INITIALIZATION_RANGE_ERROR

on an attempt to initialize a regis-

ter for which initialization is forbidden. See the sub-section INTERACTION BETWEEN INITIALIZER

FUNCTIONS above. Otherwise

_UNW_set... returns _UNW_OK on successful completion.

_UNW_clear returns _UNW_OK on successful completion. Otherwise _UNW_clear returns

_UNW_CLEAR_NOT_ALLOWED_IN_STATE when _Unwind_Context

is not in one of the following

states: Init, User_Interrupted_Frame, User_Sendsig_Frame, Kernel_Bottom_Frame, Frame. See

unwind(5).

_UNW_GR_PhysicalNumber, _UNW_FR_PhysicalNumber

, and _UNW_PR_PhysicalNumber

each return a register number. They return 0 (along with the side effect of setting the

_Unwind_Context alert code to _UNW_QUERY_RANGE_ERROR

) if passed a logical number which is

outside of the range of mapped logical numbers for that register class.

_UNW_step produces the following return codes:

_UNW_STEP_KERNEL_SAVE_STATE

Indicates _Unwind_Context describes a frame beyond which the stack unwind library

can no longer step. Any HP_UX kernel interruption frame other than the one associated

with _user_sendsig() which supports user signal handling (see signal(5)) results in

this return value.

_UNW_STEP_BOTTOM

Indicates _Unwind_Context describes a frame beyond which the stack unwind library

can no longer step. This return code is produced when _UNW_step is called for any

Section 3−−8 Hewlett-Packard Company − 3 − HP-UX 11i Version 2: September 2004