On Wed, Mar 28, 2018 at 07:47:53AM -0700, Manoj Gupta wrote:
> Please note that there is nothing wrong in the generated code, just
> that it confuses objtool.
> Clang has simply omitted the statement where NULL is returned since
> the pointer was always dereferenced post inlining.
... but returning NULL would be far more sane than falling through to
the next function.
> Note that GCC will also remove the NULL pointers if it knows that the
> pointer is dereferenced.
> Here is an example.
>
> void null_check(int *P) {
> int deref = *P;
> if (P == 0) // GCC won't check the condition.
> return;
> *P = 4;
> }
>
> Compiling with gcc -O2 gives:
> movl $4, (%rdi)
> ret
This is why we use -fno-delete-null-pointer-checks.
--
Josh
