how to setup breakpoint in gdb with shared library function

Question

I have problem with gdb, it wasn't stop in one function. Can you explain why and how to stop program after calling strcpy?

grzes@trampek:~/poligon$ gdb ./char_array2 
GNU gdb (GDB) 7.2
Copyright (C) 2010 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "i686-pc-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /home/grzes/poligon/char_array2...done.
(gdb) list
1    #include <stdio.h>
2    #include <string.h>
3    
4    int main() {
5       char str_a[20];
6       printf("ssss");
7       strcpy(str_a, "Hello, world!\n");
8       printf(str_a); 
9    }
10    
(gdb) break main
Breakpoint 1 at 0x8048465: file char_array2.c, line 4.
(gdb) run
Starting program: /home/grzes/poligon/char_array2 

Breakpoint 1, main () at char_array2.c:4
4    int main() {
(gdb) break strcpy
Breakpoint 2 at 0x1a1205
(gdb) cont
Continuing.
ssssHello, world!

Program exited with code 016.
(gdb) q
grzes@trampek:~/poligon$

Paul R · Accepted Answer · 2010-10-19 08:20:49Z

7

You may be using gcc's __builtin_strcpy. Compile with gcc -fno-builtin and see if that helps.

For more info see: http://gcc.gnu.org/onlinedocs/gcc-4.1.2/gcc/C-Dialect-Options.html#C-Dialect-Options

edited Oct 19, 2010 at 8:20

answered Oct 19, 2010 at 8:06

Paul R

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2 Comments

user480162 Over a year ago

yes, it helps - compiler changes strcpy into memcpy for optimization purpose using gcc's switches -fno-builtin prevents from such behave

Paul R Over a year ago

@user480162: gcc will automatically use __builtin_strcpy in certain cases rather than calling the standard library strcpy unless you compile with -fno-builtin. Use gcc -S to see what's being generated in your case.

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