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A re-order buffer (ROB) is used in a Tomasulo algorithm for out-of-order instruction execution. It allows instructions to be committed in-order.
Normally, there are three stages of instructions: "Issue", "Execute", "Write Result". In Tomasulo's algorithm, there is an additional stage "Commit". In this stage, the results of instructions will be stored in a register or memory. In the "Write Result" stage, the results are just put in the re-order buffer. All contents in this buffer can then be used when executing other instructions depending on these.
There are additional fields in every entry of the buffer:
Additional benefits of the re-order buffer include precise exceptions and easy rollback control of target address mispredictions (branch or jump). The ROB works by storing instructions in their original fetched order. The ROB can also be accessed from the side since each reservation station (in Tomasulo algorithm) has an additional parameter that points to instruction in the ROB. When jump prediction is not correct or a nonrecoverable exception is encountered in the instruction stream, the ROB is cleared of all instructions and reservation stations are re-initialized.
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MIPS is a reduced instruction set computer (RISC) instruction set architecture (ISA) developed by MIPS Computer Systems, now MIPS Technologies, based in the United States.
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x86 Assembly Language is a family of backward-compatible assembly languages, which provide some level of compatibility all the way back to the Intel 8008 introduced in April 1972. x86 assembly languages are used to produce object code for the x86 class of processors. Like all assembly languages, it uses short mnemonics to represent the fundamental instructions that the CPU in a computer can understand and follow. Compilers sometimes produce assembly code as an intermediate step when translating a high level program into machine code. Regarded as a programming language, assembly coding is machine-specific and low level. Assembly languages are more typically used for detailed and time critical applications such as small real-time embedded systems or operating system kernels and device drivers.
Tomasulo’s algorithm is a computer architecture hardware algorithm for dynamic scheduling of instructions that allows out-of-order execution and enables more efficient use of multiple execution units. It was developed by Robert Tomasulo at IBM in 1967 and was first implemented in the IBM System/360 Model 91’s floating point unit.
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accu, the processor transposes this name to one specific physical register on the fly. The physical registers are opaque and cannot be referenced directly but only via the canonical names.
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In software, a stack buffer overflow or stack buffer overrun occurs when a program writes to a memory address on the program's call stack outside of the intended data structure, which is usually a fixed-length buffer. Stack buffer overflow bugs are caused when a program writes more data to a buffer located on the stack than what is actually allocated for that buffer. This almost always results in corruption of adjacent data on the stack, and in cases where the overflow was triggered by mistake, will often cause the program to crash or operate incorrectly. Stack buffer overflow is a type of the more general programming malfunction known as buffer overflow. Overfilling a buffer on the stack is more likely to derail program execution than overfilling a buffer on the heap because the stack contains the return addresses for all active function calls.
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