Modules behaving differently on 32-bit and 64-bit systems?

[Maxim Dounin]

Hello!

On Mon, Oct 21, 2013 at 01:13:56AM -0400, andrewc wrote:

> Hi there,
> 
> I have built nginx 1.5.6 from source, with a 3rd party module (xtoken -
> http://code.google.com/p/nginx-xtoken-module/).
> 
> I have it working fine on a 32-bit Debian Squeeze system. An identical build
> on a 64-bit Centos 6.4 system, with an identical configuration file results
> in the error: "nginx: [crit] ngx_slab_alloc() failed: no memory" on
> startup.
> 
> I have narrowed the problem to the xtoken module, in as much as removing
> references to it on the 64-bit system results in nginx starting correctly.
> 
> I have had a quick look at the module source code, and can't see anything
> that is obviously 32-bit -centric, other than a couple of variables that
> have been declared as uint32_t.
> 
> Is it correct to assume that a properly written module will work correctly
> on both 32 and 64-bit systems?

Yes.

> Is there any additional nginx configuration that needs to be performed on
> 64-bit systems?

In some cases, additional configuration may be required due to 
different data sizes.

Quick looks suggests that the problem in xtoken module is likely 
here:

https://code.google.com/p/nginx-xtoken-module/source/browse/trunk/ngx_http_xtoken_module.c#660

It tries to estimate size of shared memory zone needed to keep 
it's data, but the estimate likely fails on 64-bit platforms due 
to internal structures of slab allocator being bigger on these 
platforms.

The same code may also unexpectedly fail in the future on internal 
slab allocator changes.

-- 
Maxim Dounin
http://nginx.org/en/donation.html