Arm Limited

Arm IP Limited

François Christopher Jacques Botman

Thomas Christopher Grocutt

Bradley John Smith

John Michael Horley

Matthias Lothar Boettcher

Michael John Williams

Jacob Eapen

Richard Roy Grisenthwaite

Simon John Craske

Balaji Venu

Daryl Wayne Bradley

Michael John Gibbs

Jack William Derek Andrew

Neil Burgess

Marianne Crowder

An apparatus and method are described for handling sealed capabilities. The apparatus has processing circuitry to perform processing operations during which access requests to memory are generated, wherein the processing circuitry is arranged to generate memory addresses for the access requests using capabilities that identify constraining information. Checking circuitry then determines whether a given access request whose memory address is generated using a given capability is permitted based on the constraining information identified by that given capability, and based on a level of trust associated with the given access request. Each capability has a capability level of trust associated therewith, and the level of trust associated with the given access request is dependent on both a current mode level of trust associated with a current mode of operation of the processing circuitry, and the capability level of trust of the given capability. At least one of the capabilities is settable as a sealed capability, and the apparatus further comprises sealed capability handling circuitry to prevent the processing circuitry performing at least one processing operation using a given sealed capability when the current mode level of trust is a lower level of trust than the capability level of trust of the given sealed capability.

Technique for handling sealed capabilities

A masked-vector-comparison instruction specifies a source vector operand comprising a plurality of source data elements, a mask value, and a comparison target operand. In response to the masked-vector-comparison instruction, an instruction decodercontrols processing circuitryto: for each active source data element of the source vector operand, determine whether the active source data element satisfies a comparison condition, based on a masked comparison between one or more compared bits of the active source data element and one or more compared bits of the comparison target operand, the mask value specifying a pattern of compared bits and non-compared bits within the comparison target operand and the active source data element; and generate a result value indicative of which of the source data elements of the source vector operand, if any, is an active source data element satisfying the comparison condition. This instruction is useful for variable length decoding operations.

Masked-vector-comparison instruction

An apparatus and method for constraining access to memory using capabilities. Processing circuitry performs operations during which access requests to memory are generated, with memory addresses for the access requests being generated using capabilities that identify constraining information. Capability checking circuitry performs a capability check operation to determine whether a given access request whose memory address is generated using a given capability is permitted based on the constraining information. Memory access checking circuitry then further constrains access to the memory by the given access request in dependence on a level of trust. The given capability has a capability level of trust associated therewith, and the level of trust associated with the given access request is dependent on both the current mode level of trust associated with the current mode of operation of the processing circuitry, and the capability level of trust of the given capability.

Technique for constraining access to memory using capabilities

Apparatus comprises a processor to execute program instructions stored at respective memory addresses, processing of the program instructions being constrained by a prevailing capability defining at least access permissions to a set of one or more memory addresses; the processor comprising: control flow change handling circuitry to perform a control flow change operation, the control flow change operation defining a control flow change target address indicating the address of a program instruction for execution after the control flow change operation; and capability generating circuitry to determine, in dependence on the control flow change target address, an address at which capability access permissions data is stored; the capability generating circuitry being configured to retrieve the capability access permissions data and to generate a capability for use as a next prevailing capability in dependence upon at least the capability access permissions data.

Apparatus and method for capability-based processing

A control table () defines information for controlling a processing component () to perform an operation. The table () comprises entries each corresponding to a variable size region defined by a first limit address and one of a second limit address and size. A binary search procedure is provided for looking up the table, comprising a number of search window narrowing steps, each narrowing a current search window of candidate entries to a narrower search window comprising fewer entries, based on a comparison of a query address against the first limit address of a selected candidate entry of the current search window. The comparison is independent of the second limit address or size of the selected candidate entry. After the search window is narrowed to a single entry, the query address is compared with the second limit address or size of that single entry.

Binary search procedure for control table stored in memory system

Data processing apparatuses, methods and computer programs are disclosed. A range definition register is arranged to store a range specifier and filtering operations are performed with respect to a specified transaction by reference to the range definition register. The range definition register stores the range specifier in a format comprising a significand and an exponent, wherein a range of data identifiers is at least partially defined by the range specifier. When the specified transaction is with respect to a data identifier within the range of data identifiers, the filtering operations performed are dependent on attribute data associated with the range of data identifiers.

Filtering based on a range specifier

An apparatus and method are provided for performing vector processing operations. In particular the apparatus has processing circuitry to perform the vector processing operations and an instruction decoder to decode vector instructions to control the processing circuitry to perform the vector processing operations specified by the vector instructions. The instruction decoder is responsive to a vector generating instruction identifying a scalar start value and wrapping control information, to control the processing circuitry to generate a vector comprising a plurality of elements. In particular, the processing circuitry is arranged to generate the vector such that the first element in the plurality is dependent on the scalar start value, and the values of the plurality of elements follow a regularly progressing sequence that is constrained to wrap as required to ensure that each value is within bounds determined from the wrapping control information. The vector generating instruction can be useful in a variety of situations, a particular use case being to implement a circular addressing mode within memory, where the vector generating instruction can be coupled with an associated vector memory access instruction. Such an approach can remove the need to provide additional logic within the memory access path to support such circular addressing.

Vector generating instruction for generating a vector comprising a sequence of elements that wraps as required

A data processing system includes processing circuitry for executing context-data-dependent program instructions which are decoded by decoder circuitry. Such context-data-dependent program instructions perform processing which is dependent upon currently existing context data. As an example, the context-data-dependent program instructions may be floating point instructions and the context data may be rounding mode information. The decoder circuitry supports a context save instruction which saves context data when it is marked as having been used and saves default context data when the current context data is marked as not having been used. The decoder circuitry further supports a context restore instruction which restores context data when the current context data is marked as having been used and permits the current context data to continue for future use when it is marked as currently unused.

Marking current context data to control a context-data-dependent processing operation to save current or default context data to a data location

In response to decoding a zero-overhead loop control instruction of an instruction set architecture, processing circuitry sets at least one loop control parameter for controlling execution of one or more iterations of a program loop body of a zero-overhead loop. Based on the at least one loop control parameter, loop control circuitry controls execution of the one or more iterations of the program loop body of the zero-overhead loop, the program loop body excluding the zero-overhead loop control instruction. Branch prediction disabling circuitry detects whether the processing circuitry is executing the program loop body of the zero-overhead loop associated with the zero-overhead loop control instruction, and dependent on detecting that the processing circuitry is executing the program loop body of the zero-overhead loop, disables branch prediction circuitry. This reduces power consumption during a zero-overhead loop when the branch prediction circuitry is unlikely to provide a benefit.

Control of branch prediction for zero-overhead loop

An apparatus comprises capability checking circuitryto perform a capability validity checking operation to determine whether use of a capability satisfies one or more use-limiting conditions. The capability comprises a pointer and pointer-use-limiting information specifying the one or more use-limiting conditions. The one or more use-limiting conditions comprise at least an allowable range of addresses for the pointer. In response to a capability write request requesting that a capability is written to a memory location associated with a capability write target address, when capability write address tracking is enabled, capability write address tracking circuitryupdates a capability write address tracking structurebased on the capability write target address.

Capability write address tracking

An apparatus and method are provided for generating and processing a trace stream indicative of instruction execution by processing circuitry. An apparatus has an input interface for receiving instruction execution information from the processing circuitry indicative of a sequence of instructions executed by the processing circuitry, and trace generation circuitry for generating from the instruction execution information a trace stream comprising a plurality of trace elements indicative of execution by the processing circuitry of instruction flow changing instructions within the sequence. The sequence may include a branch behaviour setting instruction that indicates an identified instruction within the sequence, where execution of the branch behaviour setting instruction enables a branch behaviour to be associated with the identified instruction that causes the processing circuitry to branch to a target address identified by the branch behaviour setting instruction when the identified instruction is encountered in the sequence. The trace generation circuitry is further arranged to generate, from the instruction execution information, a trace element indicative of execution behaviour of the branch behaviour setting instruction, and a trace element to indicate that the branch behaviour has been triggered on encountering the identified instruction within the sequence. This enables a very efficient form of trace stream to be used even in situations where the instruction sequence executed by the processing circuitry includes such branch behaviour setting instructions.

Apparatus and method for generating and processing a trace stream indicative of instruction execution by processing circuitry

Memory access control circuitry controls handling of a memory access request based on at least one memory access control attribute associated with a region of address space including the target address. The memory access control circuitry comprises: lookup circuitry comprising a plurality of sets of comparison circuitry, each set of comparison circuitry to detect, based on at least one address-region-indicating parameter associated with a corresponding region of address space, whether the target address is within the corresponding region of address space; region mismatch prediction circuitry to provide a region mismatch prediction indicative of which of the sets of comparison circuitry is predicted to detect a region mismatch condition; and comparison disabling circuitry to disable at least one of the sets of comparison circuitry that is predicted by the region mismatch prediction circuitry to detect the region mismatch condition for the target address.

Region mismatch prediction for memory access control circuitry

An apparatus and method are provided to control assertion of a trigger signal to processing circuitry. The apparatus has evaluation circuitry to receive program instruction execution information indicative of a program instruction executed by the processing circuitry, which is arranged to perform an evaluation operation to determine with reference to evaluation information whether the program instruction execution information indicates presence of a trigger condition. Trigger signal generation circuitry is used to assert a trigger signal to the processing circuitry in dependence on whether the trigger condition is determined to be present. Further, filter circuitry is arranged to receive event information indicative of at least one event occurring within the processing circuitry, and is arranged to determine with reference to filter control information and that event information whether a qualifying condition is present. The filter circuitry is arranged, on determining that the qualifying condition is not present, to prevent the presence of the trigger condition being notified to the trigger signal generation circuitry. This allows the monitoring of particular program instruction execution behaviour to be qualified so that the processing circuitry is only notified if in addition a qualifying event is determined to be present.

Apparatus and method for controlling assertion of a trigger signal to processing circuitry

An apparatus comprises processing circuitry, a number of vector register and a number of scalar registers. An instruction decoder is provided which supports decoding of a vector multiply-add instruction specifying at least one vector register and at least one scalar register. In response to the vector multiply-add instruction, the decoder controls the processing circuitry to perform a vector multiply-add instruction in which each lane of processing generates a respective result data element corresponding to a sum of difference of a product value and an addend value, with the product value comprising the product of a respective data element of a first vector value and a multiplier value. In each lane of processing at least one of the multiplier value and the addend value is specified as a portion of a scalar value stored in a scalar register.

Vector multiply-add instruction

An apparatus comprising data processing circuitry for processing data in one of a plurality of operating states, an instruction decoder for decoding instructions and error checking circuitry for performing error checking operations. In response to a touch instruction being decoded by the instruction decoder, error checking operation is performed on selected architectural state. The architectural state is architecturally inaccessible to the operating state. As a result of the touch instruction, the architectural state remains unchanged, at least when no error is detected.

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Cambridge, United Kingdom

François Christopher Jacques Botman