[Valgrind-users] Valgrind can't catch memory breaking by overwriting global valuable and local valuable ???

[Jack <vm...@gm...>]

Dear All

i am a rookie on valgrind
so i wrote an test program on pc to test valgrind ability of program internal memory breaking
but somehow it seems can't fetch program internal over-writing and under-writing global or local valuable??

following is my test program valtest.c , which will be compiled as valtest
if i run valgrind valtest swerr
with OVERWSTACK=1000  valgrind will catch internal memory breaking with msg
	Addr 0x0 si not stack'd, malloc'd or free'd
but if i reduce OVERWSTACK=100 , no thing happened , valgrind will end in peace 

if i set UNDERWSTACK=7, valgrind will catch out the breaking by msg addr 0xbe9c0097 is on thread1's stack , 1 bytes below stack pointer
but if i set UNDERWSTACK under 6 , its the same , no thing happened , valgrind will end in peace , 


it's the same , when i run valgrind valtest gwerr
if set OVERWGLOBAL 10000 , valgrind msg ->Addr 0x0 si not stack'd, malloc'd or free'd
but set OVERWGLOBAL 1000, valgrind will end in peace 


if set  UNDERWGLOBAL 1000 , valgrind msg ->jump to the invaild addr stated on the next line
but set UNDERWGLOBAL 10 , valgrind will end in peace 

so could anyone kindlly direct me 
how to configure valgrind to be able to catch out the internal memory breaking???

Thanks~~jack


void test(void);

char gArray[10];


void test(void){

	char cmd[10];

#define OVERWSTACK 1000
#define UNDERWSTACK 7

	for(i=0;i<OVERWSTACK;i++)
		cmd[i]='\0';

	for(i=1;i<= UNDERWSTACK;i++)
		*((char *)cmd-i)='\0';

}


int main (int argc, char *argv[])
{

		if( strcmp(argv[1],"swerr")==0 ){
			printf("valtest:cmd swerr\n");
			test();
		}
		else if( strcmp(argv[1],"gwerr")==0 ){
			int i;
			printf("valtest:cmd gwerr\n");

#define OVERWGLOBAL 10000
#define UNDERWGLOBAL 1000

			for(i=0;i<OVERWGLOBAL;i++)
				gArray[i]='\0';

			for(i=0;i<UNDERWGLOBAL;i++)
				*((char *)gArray-i)='\0';

		}

}