共有メモリ

/* Obsolete, used only for backwards compatibility and libc5 compiles */
struct shmid_ds {
        struct ipc_perm         shm_perm;       /* operation perms */
        int                     shm_segsz;      /* size of segment (bytes) */
        __kernel_time_t         shm_atime;      /* last attach time */
        __kernel_time_t         shm_dtime;      /* last detach time */
        __kernel_time_t         shm_ctime;      /* last change time */
        __kernel_ipc_pid_t      shm_cpid;       /* pid of creator */
        __kernel_ipc_pid_t      shm_lpid;       /* pid of last operator */
        unsigned short          shm_nattch;     /* no. of current attaches */
        unsigned short          shm_unused;     /* compatibility */
        void                    *shm_unused2;   /* ditto - used by DIPC */
        void                    *shm_unused3;   /* unused */
};

#include <sys/ipc.h>
#include <sys/shm.h>

int shmget(key_t key, int size, int shmflg);  

#include <sys/types.h>
#include <sys/shm.h>

void *shmat(int shmid, const void *shmaddr, int shmflg);

#include <sys/ipc.h>
#include <sys/shm.h>

int shmctl(int shmid, int cmd, struct shmid_ds *buf);  

#include <sys/types.h>
#include <sys/shm.h>

int shmdt(const void *shmaddr);  

#include	<sys/types.h>
#include	<sys/ipc.h>
#include	<sys/shm.h>
#include	<stdlib.h>

#define	ARRAY_SIZE	 40000
#define	MALLOC_SIZE	100000
#define	SHM_SIZE	100000
#define	SHM_MODE	(SHM_R | SHM_W)	/*ユーザが読み書き可能*/

char	array[ARRAY_SIZE];	/*初期化されていないデータ(bss)*/

int 
main(void)
{
	int		shmid;
	char	*ptr, *shmptr;

	/*初期化されていないデータ(bss)*/
	printf("array[] from %x to %x\n", &array[0], &array[ARRAY_SIZE]);

	/*スタック*/
	printf("stack around %x\n", &shmid);

	/*マロックサイズ100,100バイト確保*/
	if ( (ptr = malloc(MALLOC_SIZE)) == NULL)
		error("malloc error");
	printf("malloced from %x to %x\n", ptr, ptr+MALLOC_SIZE);

	/* IPC_PRIVATEをキーとしてSHM_SIZEバイトの共有メモリを新規に
	   準備し、SHM_MODEでユーザに読み書きを許す */
	if ( (shmid = shmget(IPC_PRIVATE, SHM_SIZE, SHM_MODE)) < 0)
		error("shmget error");

	/* 共有メモリの先頭をオプションなしで確保
	   これでshmptrが指すメモリは他のプロセスと共有 */
	if ( (shmptr = shmat(shmid, 0, 0)) == (void *) -1)
		error("shmat error");
	printf("shared memory attached from %x to %x\n",
				shmptr, shmptr+SHM_SIZE);

	/* 共有メモリ識別子を削除 */
	if (shmctl(shmid, IPC_RMID, 0) < 0)
		error("shmctl error");

	exit(0);
}

array[] from 8049900 to 8053540
stack around bffff7c8
malloced from 8053548 to 806bbe8
shared memory attached from 4014b000 to 401636a0