Abstract: In an embodiment, an integrated circuit may include one or more processors. Each processor may include multiple processor cores, and each core has a different design/implementation and performance level. For example, a core may be implemented for high performance, but may have higher minimum voltage at which it operates correctly. Another core may be implemented at a lower maximum performance, but may be optimized for efficiency and may operate correctly at a lower minimum voltage. The processor may support multiple processor states (PStates). Each PState may specify an operating point and may be mapped to one of the processor cores. During operation, one of the cores is active: the core to which the current PState is mapped. If a new PState is selected and is mapped to a different core, the processor may automatically context switch the processor state to the newly-selected core and may begin execution on that core.

Abstract: Systems, apparatuses, and methods for modifying access permissions in a processor. A processor may include one or more permissions registers for managing access permissions. A first permissions register may be utilized to override access permissions embedded in the page table data. A plurality of bits from the page table data may be utilized as an index into the first permissions register for the current privilege level. An attribute field may be retrieved from the first permissions register to determine the access permissions for a given memory request. A second permissions register may also be utilized to set the upper and lower boundary of a region in physical memory where the kernel is allowed to execute. A lock register may prevent any changes from being made to the second permissions register after the second permissions register has been initially programmed.

Abstract: Various techniques for processing and pre-decoding branches within an IT instruction block. Instructions are fetched and cached in an instruction cache, and pre-decode bits are generated to indicate the presence of an IT instruction and the likely boundaries of the IT instruction block. If an unconditional branch is detected within the likely boundaries of an IT instruction block, the unconditional branch is treated as if it were a conditional branch. The unconditional branch is sent to the branch direction predictor and the predictor generates a branch direction prediction for the unconditional branch.

Abstract: Methods and processors for managing load-store dependencies in an out-of-order instruction pipeline. A load store dependency predictor includes a table for storing entries for load-store pairs that have been found to be dependent and execute out of order. Each entry in the table includes hashed values to identify load and store operations. When a load or store operation is detected, the PC and an architectural register number are used to create a hashed value that can be used to uniquely identify the operation. Then, the load store dependency predictor table is searched for any matching entries with the same hashed value.

Abstract: Methods and processors for enforcing an order of memory access requests in the presence of barriers in an out-of-order processor pipeline. A speculative color is assigned to instruction operations in the front-end of the processor pipeline, while the instruction operations are still in order. The instruction operations are placed in any of multiple reservation stations and then issued out-of-order from the reservation stations. When a barrier is encountered in the front-end, the speculative color is changed, and instruction operations are assigned the new speculative color. A core interface unit maintains an architectural color, and the architectural color is changed when a barrier retires. The core interface unit stalls instruction operations with a speculative color that does match the architectural color.

Abstract: A system and method for reducing the latency of data move operations. A register rename unit within a processor determines whether a decoded move instruction is eligible for a zero cycle move operation. If so, control logic assigns a physical register identifier associated with a source operand of the move instruction to the destination operand of the move instruction. Additionally, the register rename unit marks the given move instruction to prevent it from proceeding in the processor pipeline. Further maintenance of the particular physical register identifier may be done by the register rename unit during commit of the given move instruction.

Abstract: A mechanism for evicting a cache line from a cache memory includes first selecting for eviction a least recently used cache line of a group of invalid cache lines. If all cache lines are valid, selecting for eviction a least recently used cache line of a group of cache lines in which no cache line of the group of cache lines is also stored within a higher level cache memory such as the L1 cache, for example. Lastly, if all cache lines are valid and there are no non-inclusive cache lines, selecting for eviction the least recently used cache line stored in the cache memory.

Abstract: Systems, apparatuses, methods, and computer-readable mediums for preventing return oriented programming (ROP) attacks. A compiler may insert landing pads adjacent to valid return targets in an instruction sequence. When a return instruction is executed, the processor may treat the return as suspicious if the target of the return instruction does not have an adjacent landing pad. Additionally, each landing pad may be encoded with a color, and a colored launch pad may be inserted into the instruction stream next to each return instruction. When a return instruction is executed, the processor may determine if the target of the return has a landing pad with the same color as the launch pad of the return instruction. Return-target pairs with color mismatches may be treated as suspicious and the offending process may be killed.

Abstract: A system and method for efficiently reducing the latency of initializing registers. A register rename unit within a processor determines whether prior to an execution pipeline stage it is known a decoded given instruction writes a particular numerical value in a destination operand. An example is a move immediate instruction that writes a value of 0 in its destination operand. Other examples may also qualify. If the determination is made, a given physical register identifier is assigned to the destination operand, wherein the given physical register identifier is associated with the particular numerical value, but it is not associated with an actual physical register in a physical register file. The given instruction is marked to prevent it from proceeding to an execution pipeline stage. When the given physical register identifier is used to read the physical register file, no actual physical register is accessed.

Abstract: A system may include a command queue controller coupled to a number of clusters of cores, where each cluster includes a cache shared amongst the cores. An originating core of one of the clusters may detect a global maintenance command and send the global maintenance command to the command queue controller. The command queue controller may broadcast the global maintenance command to the clusters including the originating core's cluster. Each of the cores of the clusters may execute the global maintenance command. Each cluster may send an acknowledgement to the command queue controller upon completed execution of the global maintenance command by each core of the cluster. The command queue controller may also send, upon receiving an acknowledgement from each cluster, a final acknowledgement to the originating core's cluster.

Abstract: An apparatus for performing instruction throttling for a multi-processor system is disclosed. The apparatus may include a power estimation circuit, a table, a comparator, and a finite state machine. The power estimation circuit may be configured to receive information on high power instructions issued to a first processor and a second processor, and generate a power estimate dependent upon the received information. The table may be configured to store one or more pre-determined power threshold values, and the comparator may be configured to compare the power estimate with at least one of the pre-determined power threshold values. The finite state machine may be configured to adjust the throttle level of the first and second processors dependent upon the result of the comparison.

Abstract: In an embodiment, an integrated circuit may include one or more processors. Each processor may include multiple processor cores, and each core has a different design/implementation and performance level. For example, a core may be implemented for high performance, but may have higher minimum voltage at which it operates correctly. Another core may be implemented at a lower maximum performance, but may be optimized for efficiency and may operate correctly at a lower minimum voltage. The processor may support multiple processor states (PStates). Each PState may specify an operating point and may be mapped to one of the processor cores. During operation, one of the cores is active: the core to which the current PState is mapped. If a new PState is selected and is mapped to a different core, the processor may automatically context switch the processor state to the newly-selected core and may begin execution on that core.

Abstract: In an embodiment, an integrated circuit may include one or more processors. Each processor may include multiple processor cores, and each core has a different design/implementation and performance level. For example, a core may be implemented for high performance, and another core may be implemented at a lower maximum performance, but may be optimized for efficiency. Additionally, in some embodiments, some features of the instruction set architecture implemented by the processor may be implemented in only one of the cores that make up the processor. If such a feature is invoked by a code sequence while a different core is active, the processor may swap cores to the core the implements the feature. Alternatively, an exception may be taken and an exception handler may be executed to identify the feature and activate the corresponding core.

Abstract: In an embodiment, a processor includes a multi-level dispatch circuit configured to supply operations for execution by multiple parallel execution pipelines. The multi-level dispatch circuit may include multiple dispatch buffers, each of which is coupled to multiple reservation stations. Each reservation station may be coupled to a respective execution pipeline and may be configured to schedule instruction operations (ops) for execution in the respective execution pipeline. The sets of reservation stations coupled to each dispatch buffer may be non-overlapping. Thus, if a given op is to be executed in a given execution pipeline, the op may be sent to the dispatch buffer which is coupled to the reservation station that provides ops to the given execution pipeline.

Abstract: A system and method for efficiently reducing the power consumption of register file accesses. A processor is operable to execute instructions with two or more data types, each with an associated size and alignment. Data operands for a first data type use operand sizes equal to an entire width of a physical register within a physical register file. Data operands for a second data type use operand sizes less than an entire width of a physical register. Accesses of the physical register file for operands associated with a non-full-width data type do not access a full width of the physical registers. A given numerical value may be bypassed for the portion of the physical register that is not accessed.

Abstract: A circuit for implementing a branch target buffer. The branch target buffer may include a memory that stores a plurality of entries. Each entry may include a tag value, a target value, and a prediction accuracy value. A received index value corresponding to an indirect branch instruction may be used to select one of entries of the plurality of entries, and a received tag value may then be compared to the tag value of the selected entries in the memory. An entry in the memory may be selected in response to a determination that the received tag does not match the tag value of compared entries. The selected entry may be allocated to the indirect instruction branch dependent upon the prediction accuracy values of the plurality of entries.

Abstract: Systems, processors, and methods for sharing an agent's private cache with other agents within a SoC. Many agents in the SoC have a private cache in addition to the shared caches and memory of the SoC. If an agent's processor is shut down or operating at less than full capacity, the agent's private cache can be shared with other agents. When a requesting agent generates a memory request and the memory request misses in the memory cache, the memory cache can allocate the memory request in a separate agent's cache rather than allocating the memory request in the memory cache.

Abstract: A mechanism for evicting a cache line from a cache memory includes first selecting for eviction a least recently used cache line of a group of invalid cache lines. If all cache lines are valid, selecting for eviction a least recently used cache line of a group of cache lines in which no cache line of the group of cache lines is also stored within a higher level cache memory such as the L1 cache, for example. Lastly, if all cache lines are valid and there are no non-inclusive cache lines, selecting for eviction the least recently used cache line stored in the cache memory.

Abstract: In an embodiment, a processor may be configured to fetch N instruction bytes from an instruction cache (a “fetch group”), even if the fetch group crosses a cache line boundary. A branch predictor may be configured to produce branch predictions for up to M branches in the fetch group, where M is a maximum number of branches that may be included in the fetch group. In an embodiment, a branch direction predictor may be updated responsive to a misprediction and also responsive to the branch prediction being within a threshold of transitioning between predictions. To avoid a lookup to determine if the threshold update is to be performed, the branch predictor may detect the threshold update during prediction, and may transmit an indication with the branch.

Abstract: Various techniques for processing instructions that specify multiple destinations. A first portion of a processor pipeline is configured to split a multi-destination instruction into a plurality of single-destination operations. A second portion of the pipeline is configured to process the plurality of single-destination operations. A third portion of the pipeline is configured to merge the plurality of single-destination operations into one or more multi-destination operations. The one or more multi-destination operations may be performed. The first portion of the pipeline may include a decode unit. The second portion of the pipeline may include a map unit, which may in turn include circuitry configured to maintain a list of free architectural registers and a mapping table that maps physical registers to architectural registers. The third portion of the pipeline may comprise a dispatch unit. In some embodiments, this may provide certain advantages such as reduced area and/or power consumption.