On 2/27/2013 3:02 AM, Paul Eggert wrote:
> If I'm understanding things correctly, this means the
> following little test program compiles and links OK.
> Can you please check this?
>
> extern char data_start[];
> char ch;
> int
> main ()
> {
>    return data_start == &ch;
> }

It compiles and links OK.  But maybe Andreas explained why.

> If this compiles and links, we need to find out why
> the similar usage in vm-limit.c does not link.
>
> Can you please compile the above program
> with gcc -std=gnu99 -O2 -S and see what
> the machine code looks like?

Attached.

> Also, suppose we change this test program to the following
> instead -- does this test program compile and link?
>
> extern char data_start[];
> char ch;
> int
> main ()
> {
>    return data_start < &ch;
> }

No, this gives the "undefined reference to `_data_start'" error.  Making 
that change in configure.ac fixes the problem.

Ken