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Increment shadow stack pointer 3 Tiger Lake, Zen 3: INCSSPQ r64: F3 REX.W 0F AE /5: RDSSPD r32: F3 0F 1E /1: Read shadow stack pointer into register (low 32 bits) [a] RDSSPQ r64: F3 REX.W 0F 1E /1: Read shadow stack pointer into register (full 64 bits) [a] SAVEPREVSSP: F3 0F 01 EA: Save previous shadow stack pointer RSTORSSP m64: F3 0F 01 /5
The topmost value is evaluated as a Boolean and, if true, the second topmost value is pushed back on the stack. IFTE allows a third "else" value that will be pushed back on the stack if the Boolean is false. The following example uses the IFT function to pop an object from the bottom of the stack and, if it is equal to 1, replaces it with "One":
Newer processors contain a dedicated stack engine to optimize stack operations. Pentium M was the first x86 processor to introduce a stack engine. In its implementation, the stack pointer is split among two registers: ESP O , which is a 32-bit register, and ESP d , an 8-bit delta value that is updated directly by stack operations.
Register machines also use a wider offset field for load-store opcodes. A stack machine's compact code naturally fits more instructions in cache, and therefore could achieve better cache efficiency, reducing memory costs or permitting faster memory systems for a given cost. In addition, most stack-machine instructions are very simple, made from ...
This type of stack is also known as an execution stack, program stack, control stack, run-time stack, or machine stack, and is often shortened to simply the "stack". Although maintenance of the call stack is important for the proper functioning of most software , the details are normally hidden and automatic in high-level programming languages .
FLAGS registers can be moved from or to the stack. This is part of the job of saving and restoring CPU context, against a routine such as an interrupt service routine whose changes to registers should not be seen by the calling code. Here are the relevant instructions: The PUSHF and POPF instructions transfer the 16-bit FLAGS register.
The stack is often used to store variables of fixed length local to the currently active functions. Programmers may further choose to explicitly use the stack to store local data of variable length. If a region of memory lies on the thread's stack, that memory is said to have been allocated on the stack, i.e. stack-based memory allocation (SBMA).
A stack may be implemented as, for example, a singly linked list with a pointer to the top element. A stack may be implemented to have a bounded capacity. If the stack is full and does not contain enough space to accept another element, the stack is in a state of stack overflow. A stack is needed to implement depth-first search.