Understanding multiple definitions in C program

["linu cherian" <linuc dot decode at gmail dot com>]

Hi,

Recently observed that, gcc doesnt warns/give error when i had a
private malloc definition in my C program, though it had dependency on
the libc. 

main.c
----------
#include <stdio.h>
#include <stdlib.h>


int main()
{

  printf("Calling malloc\n");

  malloc(100);
}

malloc.c
-------------
 #include <stdio.h>
#include <stdlib.h>


void *malloc(size_t x)
{
  printf("hello my malloc %lu \n", x);
  /* do nothing */
}

Makefile
-------------
all: malloc


libmalloc.so:libmalloc.o
        gcc -shared  malloc.o -o libmalloc.so

libmalloc.o: malloc.c
        gcc -fpic -c malloc.c



malloc: main.c libmalloc.so
        gcc  malloc.c main.c -L. -lfoo -o malloc


clean:
        rm -f *.a *.o


When i compiled and ran the above code, the output was,
# export LD_LIBRARY_PATH=.
#./malloc
Calling malloc
hello my malloc 100

#gcc --version
gcc (Ubuntu/Linaro 4.6.3-1ubuntu5) 4.6.3
Copyright (C) 2011 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.


1. On what criteria, does the  malloc symbol get resolved, since we
   have multiple  definitions, one in libmalloc and other libc. 

2. Wont it be better if gcc reports multiple definitions as error, since
    - allowing multiple definitions is error prone
    - there is inconsistency on  how gcc handles multiple definitions
      with regard to -static and without -static.
      (ie. with -static gcc reports error for this)

3. Could someone please help me understand why multiple definitions
   are desired in dynamic linked case ? 

Appreciate your help.

Thanks.
-- 
Linu cherian