Program counter

Program Counter - ineremented eaeh time an instruetion is exeeuted... 

It is clear that if all the program counters arc unoccupied (i.e. are in the state I 0 >), nothing at all happens all terms in the Hamiltonian start out with an annihilation operator, and all states thus remain in the state 0 > for all time. If we assume that only one of the sites 0,1,... fc sites is occupied, however, we see that only one site will always be occupied, though not necessarily the same site at different times. If we think of the occupied site, say the first site 0, as a cursor, the Hamiltonian effectively moves the cursor along the program counter sites while the operators Ai operate on the register n. Feynman shows how, by the time the cursor arrives at the final site fc, the n register has been multiplied by the entire set of desired operators Tj, T2,..., A -... 

Program Counter tracks the location of the next instruction to be executed in the program. 

Informally, our semantics represents the state of a VHDL program as a set of program counters, one per process. On each state transition, zero or more program counters advance. In this paper, wc do not exploit the deterministic nature of VHDL-87. Our reasons for assuming complete nondetcrministic execution are as follows ... 

Unfortunately, the method suffers in many cases from an important problem, namely non-termination when computing the set of reachable states. This can be a severe limitation on the use of Mdgs as a verification tool. For example, consider an abstract description of a conventional (non-pipelined) microprocessor where a state variable pc of abstract sort represents the program counter, a generic constant zero of the same abstract sort denotes the initial value of pc, and an abstract function symbol inc describes how the program counter is incremented by a non-branch instruction. The Mdg representing the set of reachable states of the microprocessor would contain states of the form... 

Context The information needed to execute a process including the contents of program counters, address and data registers, and stack pointers... 

Program counter As an internal register, it stores the memory address of next (subsequent) instmction for CPU. So as CPU executes instruction it is incremented by one (0000 to 0001). 

Program counter Register in which the location of the current instruction is stored. 

Increment the program counter by four to point to the next instruction. 

Registers are temporary storage units within the CPU. Some registers, such as the program counter and instruction register, have dedicated uses. Other registers, such as the accumulator, are used for more general purposes. 

The processor fetches an instmction in two distinct operations. In the first, it transmits the address in its program counter to the memory. In the second, the memory returns the addressed byte to the processor. The CPU stores this instruction byte in a register known as the instruction register and uses it to direct activities during the remainder... 

Parallel process Part of a program that may be executed independently. A process possesses its own program counter and address space. 

The Zero Page addressing mode fetches a byte from the instruction stream, increments the program counter PC r7 to point to the next location in the instruction stream, zero extends the fetched data to 16 bits to form the effective address and fetches the operand at that address from the memory. 

That kind of deterioration is close to the one stated for the memories. However, a refined analysis showed that sometimes, only the program counter was disturbed. Then the automated system executes a program which is not wished for (crippled execution, execution of another program, program-stop). 

Bouffard et al. described in [13], two methods to change the control flow graph of a Java Card. The first one is Eman 2, which provides a way to change the return address of the current function. This information is stored in the Java Card stack header. Once the malicious function exits during the correct execution, the program counter returns to the instruction which addresses it. The address of the jpg is also stored in the Java Card Stack header. An overflow attack success to change the return address by the address of the malicious byte code. Since there is no runtime check on the parameter, it allows a standard buffer overflow attack to modify the frame header. 

Fig. 2 (a) shows that the program counter register is the main contributor to the Hardware Exception. In average, more than 73% and 92% of the injections in the program counter register are detected by the hardware exceptions for single and double bit-flips, respectively. The majority of the detections are due to attempts to execute instructions that are not implemented or accesses to illegal addresses. 

Program counter register (Fig. 3 (a)). We see that injections in bit 1 and 2 in almost all cases have no impact. The reason for this is that the PowerPC architecture does not use these bits when the processor fetches instructions from main memory. With respect to the errors injected in bits 3 to 16, we see that the percentage of errors detected by hardware exceptions increases with increasing bit numbers, while the percentage of No Impact experiments decreases. Every error injected in bits 17 to 32 is detected by hardware exceptions. 

This result can partially be explained by the observations we made in the second part of the study where we looked at the error sensitivity of individual bits in different target locations. When we look at results presented in Fig. 3, it is clear that we are likely to increase the chance of detecting an error by means of a hardware exception if we increase the number of bit-flips injected in the target locations. This is especially obvious for the stack pointer and the program counter register, where bit-flips in certain bit positions are always detected by a hardware exception. 

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