security_layer.h

#ifndef SECURITY_LAYER_H
#define SECURITY_LAYER_H

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

extern unsigned long shadow_stack[];
extern int shadow_sp;

#ifdef ENABLE_SECURITY
#define SHADOW_PROLOGUE() { \
    __asm__ volatile ( \
        "movq 8(%%rbp), %%rax\n\t" \
        "movq %%rax, %0\n\t" \
        : "=m" (shadow_stack[shadow_sp++]) \
        : \
        : "rax" \
    ); \
}
#define SHADOW_EPILOGUE() { \
    unsigned long current_ra = (unsigned long)__builtin_return_address(0); \
    unsigned long original_ra = shadow_stack[--shadow_sp]; \
    if (current_ra != original_ra) { \
        fprintf(stderr, "\n[ALERT] Security Breach! Return address mismatch.\n"); \
        fprintf(stderr, "[Detail] Expected: %lx | Found: %lx\n", original_ra, current_ra); \
        _exit(1); \
    } \
}

#else
    // If security is disabled, macros are empty and impose no CPU overhead.
    #define SHADOW_PROLOGUE() 
    #define SHADOW_EPILOGUE()

#endif

#endif