Why are not all printf arguments shown in gdb?

Question

I am playing with gdb to debug and analyze simple C programs, e.g.

#include <stdio.h>
#include <stdlib.h>

int main() {
   int i = 8;

   printf("Your lucky number is %d\n", i);
}

When I debug in dbg and stop at printf call, gdb sees only the first argument, but not the second:

(gdb) break "printf"
Breakpoint 1 at 0x4004c0
(gdb) run
Starting program: /tmp/sq/a.out 

Breakpoint 1, __printf (format=0x4006f4 "Your lucky number is %d\n") at printf.c:28
28      printf.c: No such file or directory.

Why is that? And how to see the rest? Is it specific to printf?

(glibc 2.23, gcc 5.4, gdb 7.11.1 if that's relevant)

Possible duplicate of [gdb | view the the variable argument list](https://stackoverflow.com/questions/8242751/gdb-view-the-the-variable-argument-list) — Jean-François Fabre, Nov 12 '17 at 20:09
OK. `varargs` is what makes it special. And how to see them? The other question doesn't make it obvious to me. — Grzegorz Oledzki, Nov 12 '17 at 20:14
that's probably because it's _not_ obvious. Sounds difficult to achieve — Jean-François Fabre, Nov 12 '17 at 20:15
I would do "down" then "print i" to get the value (from caller function) — Jean-François Fabre, Nov 12 '17 at 20:18
@Jean-François Fabre and the special way the printf family is treated by some compiles (analysing the format string if possible during the compilation), makes it even more special. — 0___________, Nov 12 '17 at 20:35
Maybe XY problem. What do you want to achieve exactly? there are ways like looking at the caller, so what's preventing you to do this? — Jean-François Fabre, Nov 12 '17 at 20:36
I am trying to understand here, so maybe it's just I need an explanation for how varargs are treated when making a call. If the answer says "you can do `frame X`, then `Y`", I am fine with this. — Grzegorz Oledzki, Nov 12 '17 at 20:41
@GrzegorzOledzki after having reached the printf statement, you can do "down" to get to the caller. But you cannot get argument values automatically, you have to read the caller args and print them. — Jean-François Fabre, Nov 12 '17 at 20:43

Why are not all printf arguments shown in gdb?

0 Answers0