WARNING: in gcc 4.5.0 and 4.5.1 volatile is ignored

Hello,

because I've recently seen some other places where volatile is used to access registers without using read?() or write?() and many people seem to start using 4.5.1, I want to post this warning using a descriptive subject.

The keyword volatile might not have any effect when reading when gcc 4.5.0 or 4.5.1 is used.

The appropriate bug seems to be that one:

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45052

You might either change such code to use readb(), readw() or readl(), or you have to use either an older version of gcc or a version >= 4.5.2 (it is fixed in 4.5.2).

A patch for write?() and read?() is currently in the u-boot-arm-repository (but not in the master and not in 2010.12):

http://lists.denx.de/pipermail/u-boot/2011-January/084885.html

Regards,

Alexander

Dear Alexander Holler,

Actuelly this warning should eventually be extended to carefully check results when using any of the currently available 4.5.x versions of GCC.

This is probably only one part of the problem. Thereare a number of other bugs in thes ecompiler versions, for example this one:

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44392

Unfortunately there appears to be little interest within the GCC folks to fix porolems that affect only such lunatic fringe groups as the embedded folks, so I don't expect to see fixes any time soon. Even bigger projects like the Linux Foundation driven Poky (resp. Yocto project) capitulated and stopped using -Os, see for example here:
http://thread.gmane.org/gmane.linux.embedded.poky/2311/focus=2565

Yes, "-Os" is default setting for U-Boot - changing it to (for example) -O2 will generate significantly larger code and even break a number of boards.

It appears there are a number of other issues with GCC 4.5.x that affect us. If you are using any such tool chain, and see strange results or unexpected breakages, it is probably a very good idea to try another (older, working) tool chain first, before spending any tme on debugging.

We will take care to provide working (at least with most of the compiler versions) I/O accessors (including sufficient memory barriers), and all code that uses the old volatile pointer approach to access device registers should be converted to use proper I/O acessors.

Thanks for raising this issue again.

Best regards,

Wolfgang Denk

DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
The ideal situation is to have massive computing power right at home.
Something that dims the streetlights and shrinks the picture  on  the
neighbours' TVs when you boot it up.

What's about pulling it sooner than later into master, then?

And would it be worth to think about applying this to 2010.12 and creating a 2010.12.1?

Best regards

Dirk

Hi Dirk,

Le 22/01/2011 18:40, Dirk Behme a ?crit :

I will send out a pull request for u-boot-arm once I have applied all outstanding ARM patches from jan 17 or before and all outstanding ARM bug fixes regardless of their date, and pulled other ARM repos whose custodian requests pulling.

Amicalement,

Albert.

Dear Albert ARIBAUD,

Thanks - but I also think that Dirk's proposal to create a v2010.12.1 bug fix release makes sense. What do you think?

Best regards,

Wolfgang Denk

DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
Star Trek Lives!

Le 22/01/2011 20:30, Wolfgang Denk a ?crit :

I didn't comment on this point as it was not for me to decide upon releasing an interim U-boot version :) but I'm fine with it if you do. When I rebase on u-boot/master before sending my pull request, I'll simply skip the corresponding patch in my tree as it will already be on yours.

Amicalement,

Albert.

Dear Albert ARIBAUD,

As soon as you send the pull-request for ARM (when will that be, btw?) I will also cherry-pick that commit into a .1 stable branch.

Best regards,

Wolfgang Denk

DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
"The greatest warriors are the ones who fight for peace."
- Holly Near

Le 24/01/2011 14:03, Wolfgang Denk a ?crit :

Ok. I am going through my patchwork backlog; I might be done tomorrow evening, but more probably the day after.

Amicalement,

Albert.