CEEGOTO — restart execution at specified label

CEEGOTO is used to restart execution at a specified label within a stack frame. It is supported to work only from one language to that same language.

CEEGOTO operates within a single thread (and thus, on one stack) and can only target earlier stack frames on that stack. If the Language Environment condition manager is on the stack and the range of CEEGOTO is from a stack frame more recent than the Language Environment condition manager to a stack frame less recent than the Language Environment condition manager, the Language Environment condition manager pops off the stack and the corresponding condition handler is terminated at that point. For more deeply nested conditions, several can be canceled at once.

A return to the caller occurs only when the feedback token is provided and a condition is detected.

Syntax

void CEEGOTO (target_id, [fc])

LABEL     *target_id;
FEED_BACK *fc;

CEEGOTO

Call this CWI interface as follows:

L     R15,CEECAACELV-CEECAA(,R12)
L     R15,20(,R15)
BALR  R14,R15

target_id (input)

A label variable passed by reference. The first word of the label points to an active DSA. The DSA does not necessarily need to exist within the Language Environment-managed stack. However, it does need to be on the back chain of save areas. The second word of the label variable points to the instruction that receives control when CEEGOTO is run. If this address is zero, then the address is obtained from the saved R14 in the DSA specified in the first word. AMODE information is obtained from the high-order bit of the address.

The target_DSA_address field in the first 4 bytes of a non-XPLINK label variable is always non-zero. The base_register_instruction contains an instruction that, when run using an assembler EX instruction, restores the base register(s) needed by the target_instruction. A non-XPLINK label variable cannot be used to GOTO or resume an XPLINK routine. Figure 1 shows the format of the non-XPLINK label variable.

Figure 1. Format of a non-XPLINK label variable

The first 4 bytes of an extended label variable are zero. An extended label variable can be used to GOTO or resume either an XPLINK or non-XPLINK routine. When resuming an XPLINK routine, the resume registers are contained in the extended label variable itself, not the DSA to be resumed. Figure 2 shows the XPLINK extended format label variable.

Figure 2. XPLINK extended format label variable

Note: The storage for the label variable is expected to be allocated within the storage of the lexical scope of the label variable so that the storage is released when the lexical scope is collapsed.

Figure 3 shows the XPLINK extended format label variable – resume area.

Figure 3. XPLINK extended format label variable – resume area

Table 1. Vector Register save area

+00

Vector Register save area version

+02

(reserved)

. . .

+10

Vector Registers 0-31 (16-bytes each)

. . .

+210

Start of HLL-specific area - length not specified - can be 0 - length

fc (output/optional)

One of the following condition tokens, which are passed by reference. A return to the caller occurs only when a condition is detected.

Condition
CEE07Q	Severity	2
	Msg_No	0250
	Message	The target_id was not found on the stack.
CEE07R	Severity	2
	Msg_No	0251
	Message	An invalid target_id was provided.

Usage Notes:

As routines are popped off the stack, the DSA exit routines are invoked for those DSAs marked as an exit DSA.
The base_register_instruction in the label variable is run using the assembler instruction EX and is intended to restore the base register needed by the target instruction. This instruction is executed immediately prior to the branch to the target_instruction. The values of the registers are as follows:
R0-R12

Restored from the target_dsa

R13

The target_dsa

R14

The address of the target_instruction

R15

The address of the base_register_instruction

When resuming with an extended-format LABEL variable that resides in an XPLINK DSA or alloca() area, that area may have been freed before the base_register_instructon is executed.

When resuming into an XPLINK function, the register values when the EX instruction is executed are:

R0-R3

Restored from extended format resume area in the LABEL variable

R4

Address of the target_dsa

R5

Restored from Extended format resume area in the LABEL variable

R6

The address of the base_register_instruction. This instruction is not copied to a safe place before it is executed, so it must not reside in an XPLINK DSA or XPLINK alloca() area that will get freed when CEEGOTO runs.

R7

The address of the target_instruction

R8-R15

Restored from extended format resume area in the LABEL variable
If the base_register_instruction is zero, the EXecute is not performed.
CEEGOTO requests from a POSIX application (using longjmp() or siglongjmp()) are intercepted so that proper cleanup routine and destructor function invocation can take place. While executing a cleanup routine (for example, a routine established using CEECPSH), a CEEGOTO results in execution of all of the pushed, but not popped cleanup routines for more recent stack frame's than the target stack frame. This rule applies for both normal processing and for the execution of cleanup routines during thread termination. If the jump buffer was established in the cleanup routine (for example, the target of the CEEGOTO is in the same cleanup routine) control continues at that point.
CEEGOTO invocation while processing a destructor function (during thread termination) is allowed, but the target of the jump must be established by the destructor function. (This is required since all of the user code has been removed from the stack.)
When resuming an XPLINK routine that issues an alloca(), any alloca() requests that were done after the LABEL variable was set up will be undone. When resuming into a non-XPLINK routine, alloca() requests already made by that routine are not undone.
A non-extended format LABEL variable passed to CEEGOTO must not reside in an XPLINK DSA or alloca() area that will get freed when the program is restarted.
An extended format LABEL variable passed to CEEGOTO can reside in an XPLINK or non-XPLINK DSA that will be freed when execution is restarted. It can also reside in storage obtained using XPLINK alloca() that will be freed when execution is restarted. The LABEL variable can also reside elsewhere, in which case CEEGOTO will not free it.
When an XPLINK program is restarted, register 7 always points to the target_instruction. When a non-XPLINK program is restarted, register 14 always points to the target_instruction. This may limit the use of CEEGOTO to restarting progams at a return point after a call.
The base_register_instruction will not be copied into a safe place before CEEGOTO is executed with the EX instruction. The base_register_instruction and any operands it uses must not reside in an XPLINK DSA or XPLINK alloca() area that is freed during the processing in CEEGOTO.
Because FPRs 0-15 share the same storage with bytes 0-7 of VRs 0-15, the content of FPRs save area overrides the content of Vector Registers save area when they are both provided in extended format resume area, in the LABEL variable.