>
> > I remember a big discussion happening on LKML on this
> > topic (i.e., NULL vs 0) a couple of months back. It must
> > be still available in their mail archives. Try googling for
> > "Use NULL instead of integer 0" & you must find it. Must
> > say it was a pretty heated discussion. Dont know what
> > the outcome was. I stopped following it after sometime.
> Tried some thing and pasting a copy here...which tells clearly abt NULL
> pointer and using zero(integer)
Tried some thing and pasting a copy here...which tells clearly abt NULL
pointer and using zero(integer)
C code -- used
file name : null.c
int main()
{
int *p= NULL;
return 0;
}
file name : zero.c
int main()
{
int p = 0;
return 0;
}
Assembly snippet on 64 bit machine for null.c
main:
.LFB3:
pushq %rbp
.LCFI0:
movq %rsp, %rbp
.LCFI1:
movq $0, -8(%rbp) <------------
movl $0, %eax
leave
ret
Assembly snippet on 64 bit machine for zero.c
main:
.LFB3:
pushq %rbp
.LCFI0:
movq %rsp, %rbp
.LCFI1:
movl $0, -4(%rbp) <-------------
movl $0, %eax
leave
ret
Check out the 7th line..... of both the snippets
If we see here 8 bytes are deducted from base pointer(in 64 bit machine --
when variable p was NULL pointer)
and 4 bytes are deducted from rbp when p was integer....(obvious... Right
!!!!)
and thus the code differs.......
Whereas in 32 bit machine, assembly snippets for null.c and zero.c are
similar.
main:
pushl %ebp
movl %esp, %ebp
subl $8, %esp
andl $-16, %esp
movl $0, %eax
addl $15, %eax
addl $15, %eax
shrl $4, %eax
sall $4, %eax
subl %eax, %esp
movl $0, -4(%ebp)
movl $0, %eax
leave
ret
Interesting conclusions and concept to imbibe :)
Regards,
Vishal.
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