Abstract: Embodiments relate to selectively blocking branch instruction predictions. An aspect includes computer implemented method for performing selective branch prediction. The method includes detecting, by a processor, a branch-prediction blocking instruction in a stream of instructions and blocking, by the processor, branch prediction of a predetermined number of branch instructions following the branch-prediction blocking instruction based on the detecting the branch-prediction blocking instruction.

Abstract: Methods and systems for pre-detecting a hardware hang in a processor. The methods comprise maintaining a count of a number of cycles in a predefined time interval without an instruction being completed; detecting a pre-hang condition if said count is within N counts of a hang limit; initiating trace capture in response to detecting said pre-hang condition; and detecting a hang condition if said count equals said hang limit.

Abstract: An instruction is provided to perform clearing of selected address translation buffer entries (TLB entries) associated with a particular address space, such as segments of storage or regions of storage. The buffer entries related to segment table entries or region table entries or ASCE addresses. The instruction can be implemented by software emulation, hardware, firmware or some combination thereof.

Abstract: A computer machine instruction is fetched and executed, the machine instruction having a signed field value wherein the signed field value comprises contiguous bit positions 1-N consisting of a contiguous most significant value contiguous with a contiguous embedded sign field, the embedded sign field contiguous with a contiguous least significant value. Preferably, the sign field is one bit, the contiguous most significant value comprises bit position N and the least significant value comprises bit position 1 wherein N is the least significant bit of the most significant value.

Abstract: A method for creating precise exceptions including checkpointing an exception causing instruction. The checkpointing results in a current checkpointed state. The current checkpointed state is locked. It is determined if any of a plurality of registers require restoration to the current checkpointed state. One or more of the registers are restored to the current checkpointed state in response to the results of the determining indicating that the one or more registers require the restoring. The execution unit is restarted at the exception handler or the next sequential instruction dependent on whether traps are enabled for the exception.

Abstract: The updating of components of storage keys is managed. A control program indicates whether the updating of selected components of a storage key can be bypassed. If the updating of the selected components can be bypassed, then depending on the circumstances, an update of the storage key may not need to be performed, saving on quiesce operations. The likelihood that the updating of a storage key can be bypassed is enhanced by selecting a block of storage, along with its associated storage key, from a designated queue or designated region of a queue.

Abstract: A computer architecture that provides the definition of a 20 bit signed displacement value used to form the operand storage address.

Abstract: Selected units of storage, such as segments of storage or regions of storage, may be invalidated. The invalidation is facilitated by the setting of invalidation indicators located in data structure entries corresponding to the units of storage to be invalidated. Additionally, buffer entries associated with the invalidated units of storage or other chosen units of storage may be cleared. An instruction is provided to perform the invalidation and clearing. The instruction can be implemented by software emulation, hardware, firmware or some combination thereof.

Abstract: Disclosed is a method and apparatus providing the capability to prevent particular branches from being written into the BTB, thereby making them non-predictable. By making certain branches only detectable at decode time frame, branch prediction can completely run asynchronous of decode. By allowing branch prediction logic to cover as wide a range of branches as possible, the efficiency of fetching of branch targets way before the branch itself achieves a higher level of precision. This increased level of precision eliminates pipeline stalls between branches and targets where prior concerns of creating data integrity within the pipeline of a microprocessor existed.

Abstract: An embodiment of the invention is a method for capturing hardware trace data. A wrap-back address space is defined and during compression mode, trace data is circularly stored in the wrap-back address space. Upon exiting compression mode, a write address is established for further trace data such that trace data prior to existing compression mode is maintained.