7.1.2 C/C++ System Stack

The C/C++ compiler uses a stack to:

• Allocate local variables
• Pass arguments to functions
• Save the processor status
• Save function return addresses
• Save temporary results

The run-time stack grows up from low addresses to higher addresses. By default, the stack is allocated in the .stack section. (See the run-time-support boot.asm file.) The compiler uses the hardware stack pointer (SP) to manage this stack.

NOTE

Linking the .stack Section

The .stack section has to be linked into the low 64K of data memory. The SP is a 16-bit register and cannot access addresses beyond 64K.

For frames that exceed 63 words in size (the maximum reach of the SP offset addressing mode), the compiler uses XAR2 as a frame pointer (FP). Each function invocation creates a new frame at the top of the stack, from which local and temporary variables are allocated. The FP points at the beginning of this frame to access memory locations that cannot be referenced directly using the SP.

The stack size is set by the linker. The linker also creates a global symbol, __STACK_SIZE (for COFF) or __TI_STACK_SIZE (for EABI), and assigns it a value equal to the size of the stack in bytes. The default stack size is 1K words. You can change the size of the stack at link time by using the --stack_size linker option.

NOTE

Stack Overflow

The compiler provides no means to check for stack overflow during compilation or at run time. A stack overflow disrupts the run-time environment, causing your program to fail. Be sure to allow enough space for the stack to grow. You can use the --entry_hook option to add code to the beginning of each function to check for stack overflow; see Section 2.14.