The Stack Frame The University of New Mexico（新墨西哥大学的堆栈帧）.pdf

There are other user visible registers in some implementations of the architec- NOTE ture, but these are explicitly not part of this processor supplement. A program that uses these registers is not ABI compliant and its behavior is undefined. The Stack Frame Each called function in a program allocates a stack frame on the run-time stack, if necessary. A frame is allocated for each non-leaf function and for each leaf func- tion that requires stack storage. A non-leaf function is one that calls other func- tion(s); a leaf function is one that does not itself make any function calls. Stack frames are allocated on the run-time stack; the stack grows downward from high addresses to low addresses. Each stack frame has sufficient space allocated for: ■ local variables and temporaries. ■ saved general registers. Space is allocated only for those registers that need to be saved. For non-leaf function, $31 must be saved. If any of $16..$23 or $29..$31 is changed within the called function, it must be saved in the stack frame before use and restored from the stack frame before re- turn from the function. Registers are saved in numerical order, with high- er numbered registers saved in higher memory addresses. The register save area must be doubleword (8 byte) aligned. ■ saved floating-point registers. Space is allocated only for those registers that need to be saved. If any of $f20..$f30 is changed within the called func- tion, it must be saved in the stack frame before use and restored from the stack frame before return from the function. Both even- and odd-num- bered registers must be saved and restored, even if only single-precision operations are performed since the single-precision operations leave the odd-numbered register contents undefined.