SCS是Stack Chain Structure的缩写，用于管理栈帧的结构。在arm64架构上，SCS包含五个连续的栈帧，在栈下面的区域，用寄存器x18指向SCS的底部。可以使用下面的代码来获取x18寄存器中的SCS栈顶指针：

#include 
#include 

void* get_scs_top(void) {
    void* top;

    // Get current stack pointer.
    __asm__ volatile ("mov %0, sp" : "=r" (top));

    // Round up to next SCS alignment boundary.
    uintptr_t scs_align = 16 * sizeof(void*);
    uintptr_t top_int = (uintptr_t)top;
    uintptr_t scs_bot_int = (top_int + scs_align - 1) & -scs_align;

    // Calculate SCS top pointer.
    size_t num_frames = 5;
    size_t scs_size = num_frames * 16 * sizeof(void*);
    top_int = scs_bot_int + scs_size;
    top = (void*)top_int;

    return top;
}