u-boot/common/cmd_display.c
Wolfgang Denk 54841ab50c Make sure that argv[] argument pointers are not modified.
The hush shell dynamically allocates (and re-allocates) memory for the
argument strings in the "char *argv[]" argument vector passed to
commands.  Any code that modifies these pointers will cause serious
corruption of the malloc data structures and crash U-Boot, so make
sure the compiler can check that no such modifications are being done
by changing the code into "char * const argv[]".

This modification is the result of debugging a strange crash caused
after adding a new command, which used the following argument
processing code which has been working perfectly fine in all Unix
systems since version 6 - but not so in U-Boot:

int main (int argc, char **argv)
{
	while (--argc > 0 && **++argv == '-') {
/* ====> */	while (*++*argv) {
			switch (**argv) {
			case 'd':
				debug++;
				break;
			...
			default:
				usage ();
			}
		}
	}
	...
}

The line marked "====>" will corrupt the malloc data structures and
usually cause U-Boot to crash when the next command gets executed by
the shell.  With the modification, the compiler will prevent this with
an
	error: increment of read-only location '*argv'

N.B.: The code above can be trivially rewritten like this:

	while (--argc > 0 && **++argv == '-') {
		char *arg = *argv;
		while (*++arg) {
			switch (*arg) {
			...

Signed-off-by: Wolfgang Denk <wd@denx.de>
Acked-by: Mike Frysinger <vapier@gentoo.org>
2010-07-04 23:55:42 +02:00

78 lines
1.9 KiB
C

/*
* (C) Copyright 2005
* Wolfgang Denk, DENX Software Engineering, wd@denx.de.
*
* See file CREDITS for list of people who contributed to this
* project.
*
* 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 <common.h>
#include <command.h>
#undef DEBUG_DISP
#define DISP_SIZE 8
#define CWORD_CLEAR 0x80
#define CLEAR_DELAY (110 * 2)
int do_display (cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
{
int i;
int pos;
/* Clear display */
*((volatile char*)(CONFIG_SYS_DISP_CWORD)) = CWORD_CLEAR;
udelay(1000 * CLEAR_DELAY);
if (argc < 2)
return (0);
for (pos = 0, i = 1; i < argc && pos < DISP_SIZE; i++) {
char *p = argv[i], c;
if (i > 1) {
*((volatile uchar *) (CONFIG_SYS_DISP_CHR_RAM + pos++)) = ' ';
#ifdef DEBUG_DISP
putc(' ');
#endif
}
while ((c = *p++) != '\0' && pos < DISP_SIZE) {
*((volatile uchar *) (CONFIG_SYS_DISP_CHR_RAM + pos++)) = c;
#ifdef DEBUG_DISP
putc(c);
#endif
}
}
#ifdef DEBUG_DISP
putc('\n');
#endif
return (0);
}
/***************************************************/
U_BOOT_CMD(
display, CONFIG_SYS_MAXARGS, 1, do_display,
"display string on dot matrix display",
"[<string>]\n"
" - with <string> argument: display <string> on dot matrix display\n"
" - without arguments: clear dot matrix display"
);