Why exported const value modified by another driver not updated in original driver

On Tue, Sep 4, 2012 at 4:09 PM, Julian Andres Klode [off-list ref] wrote:

On Tue, Sep 04, 2012 at 03:58:20PM +0530, Manavendra Nath Manav wrote:

quoted

On Tue, Sep 4, 2012 at 3:00 PM, Manavendra Nath Manav
[off-list ref] wrote:

quoted

Hi,

I have declared a static const int variable in one driver and exported
that variable symbol. In another driver i am modifying that variable.

No, you did not export it. It's static (and static is kind of the opposite
of extern). And then you try to assign a value to a non-static variable with
the same name, which might not even exist (as the other is static, this should
not even work in my opinion).

quoted

quoted

The other driver prints the modified value but the original driver
retains the original value. When both virtual and physical addresses
of the variable as seen by both drivers are same, how is this even
possible. Is it a kernel bug?

It only works because the compiler optimized the value = 123 away,
and replaced value with 123 in the first module everywhere, as it
is declared const and thus cannot be changed, so there's no reason
to read it from memory.

--
Julian Andres Klode  - Debian Developer, Ubuntu Member

See http://wiki.debian.org/JulianAndresKlode and http://jak-linux.org/.

Still I am not able to understand !! Why the output behaviour changes
when the declaration is made as "const volatile". I get the same
results as above when i remove "static" and retain "const".
-- 
Manavendra Nath Manav