GDB script example

debug.log

Reading symbols from ~/gist/gist-4077328/gdb_test...done.
Breakpoint 1 at 0x4005cf: file gdb_test.c, line 7.

Breakpoint 1, output (val=91652772) at gdb_test.c:7
7		printf("OUTPUT: %X\n",val);
#0  output (val=91652772) at gdb_test.c:7
#1  0x0000000000400632 in rand_output (prev=4294967295, mid=1073741824, mask=2147483647) at gdb_test.c:16
#2  0x000000000040066a in main () at gdb_test.c:23

Breakpoint 1, output (val=4481602) at gdb_test.c:7
7		printf("OUTPUT: %X\n",val);
#0  output (val=4481602) at gdb_test.c:7
#1  0x0000000000400632 in rand_output (prev=31378967, mid=8388608, mask=16777215) at gdb_test.c:16
#2  0x0000000000400626 in rand_output (prev=54019494, mid=16777216, mask=33554431) at gdb_test.c:14
#3  0x0000000000400626 in rand_output (prev=131004178, mid=33554432, mask=67108863) at gdb_test.c:14
#4  0x0000000000400626 in rand_output (prev=211331964, mid=67108864, mask=134217727) at gdb_test.c:14
#5  0x0000000000400626 in rand_output (prev=403325717, mid=134217728, mask=268435455) at gdb_test.c:14
#6  0x0000000000400626 in rand_output (prev=602224003, mid=268435456, mask=536870911) at gdb_test.c:14
#7  0x0000000000400626 in rand_output (prev=1661342506, mid=536870912, mask=1073741823) at gdb_test.c:14
#8  0x0000000000400626 in rand_output (prev=4294967295, mid=1073741824, mask=2147483647) at gdb_test.c:14
#9  0x000000000040066a in main () at gdb_test.c:23

Breakpoint 1, output (val=187268169) at gdb_test.c:7
7		printf("OUTPUT: %X\n",val);
#0  output (val=187268169) at gdb_test.c:7
#1  0x0000000000400632 in rand_output (prev=4294967295, mid=1073741824, mask=2147483647) at gdb_test.c:16
#2  0x000000000040066a in main () at gdb_test.c:23

Breakpoint 1, output (val=289668203) at gdb_test.c:7
7		printf("OUTPUT: %X\n",val);
#0  output (val=289668203) at gdb_test.c:7
#1  0x0000000000400632 in rand_output (prev=4294967295, mid=1073741824, mask=2147483647) at gdb_test.c:16
#2  0x000000000040066a in main () at gdb_test.c:23
OUTPUT: 57682A4
OUTPUT: 446242
OUTPUT: B297C49
OUTPUT: 1143FC6B
[Inferior 1 (process 23466) exited normally]

gdb_ex.gdb

set breakpoint pending on
set pagination off
b output
command
    bt
    c
end
r
q

gdb_test.c

#include<stdio.h>
#include<stdlib.h>
#include<stdint.h>
#include<time.h>
void output(uint32_t val)
{
	printf("OUTPUT: %X\n",val);
}
void rand_output(uint32_t prev,uint32_t mid,uint32_t mask)
{
	uint32_t r;
	r=rand()&mask;
	if(r>mid)
		rand_output(r,mid>>1,mask>>1);
	else
		output(r);
}
int main()
{
	int i;
	srand(time(NULL));
	for(i=0;i<4;++i)
		rand_output(0xFFFFFFFF,0x40000000,0x7FFFFFFF);
	return 0;
}