Re: OT: gcc warning: implicit declaration of function

[Bryce Schober <bryceman at dpzone dot com>]

Dan Kegel wrote:

> Looks like /usr/local/lib/gcc-lib/arm-elf/3.3/include/stdlib.h
> is nearly empty on your system.  



/usr/local/lib/gcc-lib/arm-elf/3.3/include/stdlib.h:
\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
#ifndef __stdlib_h
#define __stdlib_h

#define __need_size_t
#include <stddef.h>

#if defined(__USE_FIXED_PROTOTYPES__) || defined(__cplusplus) || defined 
(__STRICT_ANSI__)
#ifndef abort
extern void abort (void);
#endif
extern int abs (int);
<snip>
#endif /* defined(__USE_FIXED_PROTOTYPES__) || ... */
#define EXIT_FAILURE 1
#define EXIT_SUCCESS 0
#endif /* __stdlib_h */
/////////////////////////////////////////////////////////////



Furthermore, doing a full compile (no -c) results in something that 
looks reasonable.


test.c
\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
#include <stdlib.h>
int main(int argc, char *argv[])
{
	int a = abs(argv[0]);
	return a;
}
/////////////////////////////////////////////////////////////


arm-elf-objdump -DS test.o
\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
test.o:     file format elf32-littlearm

Disassembly of section .text:

00000000 <main>:
#include <stdlib.h>

int main(int argc, char *argv[])
{
   0:	e1a0c00d 	mov	ip, sp
   4:	e92dd800 	stmdb	sp!, {fp, ip, lr, pc}
   8:	e24cb004 	sub	fp, ip, #4	; 0x4
   c:	e24dd00c 	sub	sp, sp, #12	; 0xc
  10:	e50b0010 	str	r0, [fp, -#16]
  14:	e50b1014 	str	r1, [fp, -#20]
	int a = abs(argv[0]);
  18:	e51b3014 	ldr	r3, [fp, -#20]
  1c:	e5933000 	ldr	r3, [r3]
  20:	e3530000 	cmp	r3, #0	; 0x0
  24:	b2633000 	rsblt	r3, r3, #0	; 0x0
  28:	e50b3018 	str	r3, [fp, -#24]

	return a;
  2c:	e51b3018 	ldr	r3, [fp, -#24]
}
  30:	e1a00003 	mov	r0, r3
  34:	e91ba800 	ldmdb	fp, {fp, sp, pc}
Disassembly of section .data:
/////////////////////////////////////////////////////////////

Sure, it's optimized out any function call, but I'd want that to happen! 
 Why do I get the warning when it builds correctly anyway?  Am I 
missing one of those defines that the stdlib.h needs, and why?

Thanks.


--
Bryce Schober
Design Engineer
Dynon Avionics, Inc.
www.dynonavionics.com

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