On 7/27/17 1:52 PM, H. S. Teoh via Digitalmars-d wrote:
On Thu, Jul 27, 2017 at 11:03:02AM -0400, Steven Schveighoffer via
Digitalmars-d wrote:
[...]
However, there do exist places where dereferencing null may NOT cause
a segmentation fault. For example, see this post by Moritz Maxeiner:
https://forum.dlang.org/post/[email protected]
In such cases, the compiled program can have no knowledge that the
zero page is mapped somehow. There is no way to prevent it, or
guarantee it during compilation.
[...]
There is one flaw with Moritz's example: if the zero page is mapped
somehow, that means 0 is potentially a valid address of a variable, and
therefore checking for null is basically not only useless but wrong: a
null check of the address of this variable will fail, yet the pointer is
actually pointing at a valid address that just happens to be 0. IOW, if
the zero page is mapped, we're *already* screwed anyway, might as well
just give up now.
Very true. You wouldn't want to store anything there as any @safe code
could easily get a pointer to that data at any time!
Either way, the guarantees of @safe go out the window if dereferencing
null is not a crashing error.
-Steve
