Re: -nostdlib option!

[Axel Freyn <axel-freyn@gmx.de>]

Hi Ali,
On Tue, Feb 15, 2011 at 11:06:08AM +0330, ali hagigat wrote:
> I am compiling my C programs with -nostdlib option without providing
> mem functions like memcpy and GNU tool chain has not complained so
> far(gcc 4.4.2, Fedora 12). Is that natural? I have defined char
> pointers, nested functions and no error so far. I wonder if anybody
> can write a simple C program and compile it with -nostdlib so that the
> compiler needs one of mem functions and the compiler stops with an
> error.
try the program:
int main(){
  char *c = (char*) malloc(10*sizeof(char));
  free(c);
}
On my machine (gcc-4.3.2), this compiles fine without the switch (just
warning about the missing header file):
~> gcc nostdlib.c
nostdlib.c: In function ‘main’:
nostdlib.c:2: warning: incompatible implicit declaration of built-in function ‘malloc’

and with "-nostdlib", it gives the link error as expected:
~> gcc -nostdlib nostdlib.c
nano-th2 ~ $ gcc -nostdlib nostdlib.c
nostdlib.c: In function ‘main’:
nostdlib.c:2: warning: incompatible implicit declaration of built-in function ‘malloc’
nostdlib.c:3: warning: incompatible implicit declaration of built-in function ‘free’
/usr/bin/ld: warning: cannot find entry symbol _start; defaulting to 00000000004000e8
/tmp/cckDrpxw.o: In function `main':
nostdlib.c:(.text+0xe): undefined reference to `malloc'
nostdlib.c:(.text+0x1b): undefined reference to `free'
collect2: ld returned 1 exit status

Adding "#include <stdlib.h>" does not solve the problem, just removes
the warning.

Axel

> 
> 
> On 2/15/11, Patrick Horgan <phorgan1@yahoo.com> wrote:
> > On 02/07/2011 04:44 AM, ali hagigat wrote:
> >> Thank you Manuel.
> >> How will be memset, memcpy, etc. Can i copy them from the source code
> >> of gcc? But they are dependent to other functions in other libraries
> >> probably and some headers.
> >> Are those functions available stand alone some where?
> >>
> >>
> >> On Mon, Feb 7, 2011 at 2:51 PM, Manuel Coutinho
> >>> Hi
> >>>
> >>> Other mechanism: supply your own memset, memcpy, etc.
> >>> If you do this, the linker will know which memset, memcpy, etc to use and
> >>> will not complaint about not using libc.
> >>>
> >>> Regards
> >>> Manuel Coutinho
> >>>
> > you would just write your own copies of these methods.  These are very
> > simple functions any beginning computer science student could write in a
> > few minutes.  For example:
> >
> > void *memset(void *s, int c, size_t n)
> > {
> >      size_t ctr;
> >      char *ptr=s;
> >      for(ctr=0;ctr<n;ctr++){
> >          *(ptr+ctr)=(char)c;
> >      }
> >      return s;
> > }
> >
> >
> >