Issue in using mmap on ARM target

Issue in using mmap on ARM target

[naveen yadav]

[-- Attachment #1: Type: text/plain, Size: 580 bytes --]

Hi all,

I am facing one issue when executing below progmra on ARM target. The
same program work well on X86 host machine,

When execute on Host(x86). the result are as expected.
[root@localhost naveen]# ./a.out  0000 b 2
/dev/mem opened.
Memory mapped at address 0xb7f00000.
Value at address 0x0 (0xb7f00000): 0x24
Written 0x2; readback 0x2

But when execute on Target:
# ./a.out 0 w 20
/dev/mem opened.
Memory mapped at address 0x40003000.
Value at address 0x0 (0x40003000): 0xEA000006
Written 0x14; readback 0xEA000006
#
The value does not change. any idea ....


Kind regards

[-- Attachment #2: devmem2.c --]
[-- Type: application/octet-stream, Size: 3551 bytes --]

/*
 * devmem2.c: Simple program to read/write from/to any location in memory.
 *
 *  Copyright (C) 2000, Jan-Derk Bakker (jdb@lartmaker.nl)
 *
 *
 * This software has been developed for the LART computing board
 * (http://www.lart.tudelft.nl/). The development has been sponsored by
 * the Mobile MultiMedia Communications (http://www.mmc.tudelft.nl/)
 * and Ubiquitous Communications (http://www.ubicom.tudelft.nl/)
 * projects.
 *
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 */

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <signal.h>
#include <fcntl.h>
#include <ctype.h>
#include <termios.h>
#include <sys/types.h>
#include <sys/mman.h>
  
#define FATAL do { fprintf(stderr, "Error at line %d, file %s (%d) [%s]\n", \
  __LINE__, __FILE__, errno, strerror(errno)); exit(1); } while(0)
 
#define MAP_SIZE 4096UL
#define MAP_MASK (MAP_SIZE - 1)

int main(int argc, char **argv) {
    int fd;
    void *map_base, *virt_addr; 
	unsigned long read_result, writeval;
	off_t target;
	int access_type = 'w';
	
	if(argc < 2) {
		fprintf(stderr, "\nUsage:\t%s { address } [ type [ data ] ]\n"
			"\taddress : memory address to act upon\n"
			"\ttype    : access operation type : [b]yte, [h]alfword, [w]ord\n"
			"\tdata    : data to be written\n\n",
			argv[0]);
		exit(1);
	}
	target = strtoul(argv[1], 0, 0);

	if(argc > 2)
		access_type = tolower(argv[2][0]);


    if((fd = open("/dev/mem", O_RDWR | O_SYNC)) == -1) FATAL;
    printf("/dev/mem opened.\n"); 
    fflush(stdout);
    
    /* Map one page */
    map_base = mmap(0, MAP_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, target & ~MAP_MASK);
    if(map_base == (void *) -1) FATAL;
    printf("Memory mapped at address %p.\n", map_base); 
    fflush(stdout);
    
    virt_addr = map_base + (target & MAP_MASK);
    switch(access_type) {
		case 'b':
			read_result = *((unsigned char *) virt_addr);
			break;
		case 'h':
			read_result = *((unsigned short *) virt_addr);
			break;
		case 'w':
			read_result = *((unsigned long *) virt_addr);
			break;
		default:
			fprintf(stderr, "Illegal data type '%c'.\n", access_type);
			exit(2);
	}
    printf("Value at address 0x%X (%p): 0x%X\n", target, virt_addr, read_result); 
    fflush(stdout);

	if(argc > 3) {
		writeval = strtoul(argv[3], 0, 0);
		switch(access_type) {
			case 'b':
				*((unsigned char *) virt_addr) = writeval;
				read_result = *((unsigned char *) virt_addr);
				break;
			case 'h':
				*((unsigned short *) virt_addr) = writeval;
				read_result = *((unsigned short *) virt_addr);
				break;
			case 'w':
				*((unsigned long *) virt_addr) = writeval;
				read_result = *((unsigned long *) virt_addr);
				break;
		}
		printf("Written 0x%X; readback 0x%X\n", writeval, read_result); 
		fflush(stdout);
	}
	
	if(munmap(map_base, MAP_SIZE) == -1) FATAL;
    close(fd);
    return 0;
}

Re: Issue in using mmap on ARM target

[Mikael Pettersson]

naveen yadav writes:
 > Hi all,
 > 
 > I am facing one issue when executing below progmra on ARM target. The
 > same program work well on X86 host machine,
 > 
 > When execute on Host(x86). the result are as expected.
 > [root@localhost naveen]# ./a.out  0000 b 2
 > /dev/mem opened.
 > Memory mapped at address 0xb7f00000.
 > Value at address 0x0 (0xb7f00000): 0x24
 > Written 0x2; readback 0x2
 > 
 > But when execute on Target:
 > # ./a.out 0 w 20
 > /dev/mem opened.
 > Memory mapped at address 0x40003000.
 > Value at address 0x0 (0x40003000): 0xEA000006
 > Written 0x14; readback 0xEA000006
 > #
 > The value does not change. any idea ....

You might have better luck getting an informed answer by posting
to linux-arm-kernel@lists.infradead.org instead.

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>