Re: [microblaze-uclinux] Microblaze with MMU, loadable module printk problems

[John Williams <jwilliams@xxxxxxxxxxxxxx>]

Hi Jeffry,

Thanks for the detailed report - comments inline below

jeffrey.fuller@xxxxxxxxx wrote:

> John, thanks for the help. I had erred in saying that the driver would 
> not do printks correctly on non-MMU Microblaze. The module you sent 
> prints correctly and so do ones I build (long story short: I fooled 
> myself into thinking the same problem was on both non-MMU and MMU).

OK, that's a good start.

> However, we do still have a problem on Microblaze with MMU, and today we 
> discovered something interesting by accident. This can be recreated with 
> the following code and method:

<snip>

> 1. Build the above module with the mb-linux-gcc compiler (as I 
> understand it, this is the compiler that should be used for Microblaze 
> w/ MMU).
>
> 2. insmod the resulting module.
>
> 3. Expected output:
> 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
> a b c d e f g h i j  k  l  m  n  o  p  q  r  s  t
>
> 4. Actual output:
>  3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
>
> 5. Now, build the above module with the microblaze-uclinux-gcc (as I 
> understand it, this is the compiler that should be used for NON-MMU 
> Microblaze).
>
> 6. insmod the resulting module.
>
> 7. You get the expected output.

Hmm.   I'll try this myself later today.

> So, in conclusion, when building a module for Microblaze w/ MMU and 
> using the mb-linux-gcc compiler, which is the compiler we thought should 
> be used, we get incorrect results. When using the 
> microblaze-uclinux-gcc, we get expected results. Again, to reiterate, 
> this is all on Microblaze w/ MMU. One further note: in our experience, 
> just about any combination of printks and strings (including, for 
> example printk("This is a string\n") should have problems when compiled 
> with mb-linux-gcc, though we have seen a few simple, single strings 
> print correctly.
>
> Can anyone tell me if we've somehow got our understanding of the 
> compilers mixed up? Or is there a real bug here? Can anyone try the 
> above test code and method on a Microbaze MMIU? Any help would be 
> greatly appreciated.

Your understanding is correct.  For building the kernel we don't really 
care if the toolchain is or is not MMU aware - the real difference is in 
the apps and libs.

That said, building kernels (and modules) with the new toolchain has to 
work!

I'll do some tests here and get back to you.

Cheers,

John


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