ch03-memaddr.c

linux编程精髓 源代码

/*
 * ch03-memaddr.c --- Show address of code, data and stack sections,
 *                    as well as BSS and dynamic memory.
 */

#include <stdio.h>
#include <malloc.h>		/* for definition of ptrdiff_t on GLIBC */
#include <unistd.h>
#include <alloca.h>		/* for demonstration only */

extern void afunc(void);	/* a function for showing stack growth */

int bss_var;			/* auto init to 0, should be in BSS */
int data_var = 42;		/* init to nonzero, should be data */

int
main(int argc, char **argv)	/* arguments aren't used */
{
	char *p, *b, *nb;

	printf("Text Locations:\n");
	printf("\tAddress of main: %p\n", main);
	printf("\tAddress of afunc: %p\n", afunc);

	printf("Stack Locations:\n");
	afunc();

	p = (char *) alloca(32);
	if (p != NULL) {
		printf("\tStart of alloca()'ed array: %p\n", p);
		printf("\tEnd of alloca()'ed array: %p\n", p + 31);
	}

	printf("Data Locations:\n");
	printf("\tAddress of data_var: %p\n", & data_var);

	printf("BSS Locations:\n");
	printf("\tAddress of bss_var: %p\n", & bss_var);

	b = sbrk((ptrdiff_t) 32);	/* grow address space */
	nb = sbrk((ptrdiff_t) 0);
	printf("Heap Locations:\n");
	printf("\tInitial end of heap: %p\n", b);
	printf("\tNew end of heap: %p\n", nb);

	b = sbrk((ptrdiff_t) -16);	/* shrink it */
	nb = sbrk((ptrdiff_t) 0);
	printf("\tFinal end of heap: %p\n", nb);
}

void
afunc(void)
{
	static int level = 0;		/* recursion level */
	auto int stack_var;		/* automatic variable, on stack */

	if (++level == 3)		/* avoid infinite recursion */
		return;

	printf("\tStack level %d: address of stack_var: %p\n",
			level, & stack_var);
	afunc();			/* recursive call */
}