The specific assembly language available on a machine is defined by the instruction set architecture (ISA) of that machine. To identify the underlying architecture of a particular Linux machine, use the uname -p command.

Every ISA defines a set of basic registers that the CPU uses to operate on data. Some registers are general purpose and can hold any kind of data, whereas other registers are special purpose and are typically reserved by the compiler for specific uses (e.g., stack pointer, base pointer). While general purpose registers are readable and writable, some special purposes registers are read-only (e.g., the instruction pointer).

The ISA also defines a series of instructions that specify operations that the CPU can perform. Each instruction has an operation code (opcode) that specifies what the instruction does, and one or more operands that specifies the data to be used. The ISA documents specific instructions for data movement, arithmetic operations, conditionals, branches, and accessing memory. These core instructions are often combined to represent more complex data structures like arrays, structs, and matrices.

The compiler uses the stack (or stack memory) of a process’s virtual address space to store temporary data. On all modern systems, the program stack grows toward lower memory addresses. The compiler uses the stack pointer and base pointer to specify a stack frame that defines the area of the stack that is associated with a particular function or procedure. A new stack frame is added to the stack with every function call and defines the stack region associated with the callee function. The stack frame associated with a particular function is removed from the stack when that function returns. Typically, the stack and base pointers return to their original values when a function ends. While this bit of bookkeeping suggests that local variables are "cleaned" from the stack, old data usually sticks around in the form of junk values, which can sometimes lead to hard-to-debug behaviors. Malicious actors can also use knowledge of an ISA’s stack bookkeeping to create dangerous security exploits, like buffer overflows.

While all systems are vulnerable to security vulnerabilities like buffer overflow, the relatively recent ARMv8-A has had the opportunity to learn from some of the security flaws that affected older Intel architectures. However, the first line of defense is always the programmer. Even with additional protections, no ISA is invulnerable to potential security flaws. When coding in C, programmers should use length specifiers whenever possible to reduce the chance of security vulnerabilities resulting from boundary overruns (see Table 1).