Gdb and external functions

Question

So I have the following code

(gdb) list #include<stdio.h> #include<string.h> int main() { char str_a[20]; strcpy(str_a,"Hello World!\n"); printf(str_a); }

But when I disassemble it with gdb, strcpy isn't referenced. Instead the inside of the function strcpy is shown.

(gdb) disassemble main Dump of assembler code for function main: 0x00000000004004fd <+0>: push rbp 0x00000000004004fe <+1>: mov rbp,rsp 0x0000000000400501 <+4>: sub rsp,0x20 0x0000000000400505 <+8>: lea rax,[rbp-0x20] 0x0000000000400509 <+12>: movabs rdx,0x6f57206f6c6c6548 0x0000000000400513 <+22>: mov QWORD PTR [rax],rdx 0x0000000000400516 <+25>: mov DWORD PTR [rax+0x8],0x21646c72 0x000000000040051d <+32>: mov WORD PTR [rax+0xc],0xa 0x0000000000400523 <+38>: lea rax,[rbp-0x20] 0x0000000000400527 <+42>: mov rdi,rax 0x000000000040052a <+45>: mov eax,0x0 0x000000000040052f <+50>: call 0x4003e0 <printf@plt> 0x0000000000400534 <+55>: leave 0x0000000000400535 <+56>: ret End of assembler dump.

How can I get GDB to reference strcpy the way it references printf? I'm compiling with "gcc -g"

Try compiling with -O0. Call strcpy() might have optimized to make it as inline function. — Rohan
– Rohan, Commented Mar 21, 2014 at 6:42
According to gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html strcpy is a function that can be replaced with a builtin function. — user184968
– user184968, Commented Mar 21, 2014 at 6:46
Looks to me like the compiler is free to do just about anything with your code, given the undefined behaviour from accessing uninitialised memory after char str_a[20];. — user3185968
– user3185968, Commented Mar 21, 2014 at 15:28

Lee Duhem · Accepted Answer · 2014-03-21 06:43:13Z

Try compiling your program with -fno-builtin.

In your gcc, strcpy is a builtin function. See also 6.56 Other Built-in Functions Provided by GCC.

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