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gdb breakpoint problem

hi, all
I am new to gdb and have trouble in setting the breakpoint. The
problem is, the program does not stop at some of the breakpoints. I am
using gdb6.6 in centos4.4. Here is the detail.

/* sample.c -- Sample C program to be debugged with ddd
#include <stdio.h>
#include <stdlib.h>
static void shell_sort(int a[], int size){
	int i, j;	
	int h = 1;
	do {
		h = h * 3 + 1;
	} while (h <= size);
	do {
		h /= 3;
		for (i = h; i < size; i++){
			int v = a[i];
			for (j = i; j >= h && a[j - h] > v; j -= h)
				a[j] = a[j - h];
			if (i != j)
			a[j] = v;
	} while (h != 1);

int main(int argc, char *argv[]){
	int *a;  //line 24
	int i; //line 25
	a = (int *)malloc((argc - 1) * sizeof(int)); // line 26
	for (i = 0; i < argc - 1; i++)
		a[i] = atoi(argv[i + 1]);
	shell_sort(a, argc);
	for (i = 0; i < argc - 1; i++)
		printf("%d ", a[i]);
	return 0;
gcc -g -o sample sample.c

gdb sample
GNU gdb 6.6
Copyright (C) 2006 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB.  Type "show warranty" for details.
This GDB was configured as "i686-pc-linux-gnu"...
Using host libthread_db library "/lib/tls/".
(gdb) break 24
Breakpoint 1 at 0x804850b: file sample.c, line 24.
(gdb) info break 1
Num Type           Disp Enb Address    What
1   breakpoint     keep y   0x0804850b in main at sample.c:24
(gdb) run 2 4 6 3 5 7
Starting program: /home/amdx2/drive2/cpp/testddd/sample 2 4 6 3 5 7

Breakpoint 1, main (argc=7, argv=0xbff515c4) at sample.c:26
26              a = (int *)malloc((argc - 1) * sizeof(int));

As you can see, the program did not stop at the breakpoint on line24.
It stops at line26. If I add another breakpoint on line25, this 2nd
breakpoint is skipped as well and the program stops at line26. Why is
that? How can I correct it?

On my own program which is rather big, it got the same problem. When I
use info break xxx, it sometimes point to a different place in "What".
For example, I placed the breakpoint in main line 100, but the "what"
points to other functions in different line. As the result, these
breakpoints never work. I changed my gcc flags with combinations of
-glevel -olevel, the problem did not solve. Thanks for your comments.


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