linux-kernel - Re: linker-tables v5 testing

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Message-ID: <20161130140947.3ea27d9e@roar.ozlabs.ibm.com>
Date:   Wed, 30 Nov 2016 14:09:47 +1100
From:   Nicholas Piggin <npiggin@...il.com>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>
Cc:     Guenter Roeck <linux@...ck-us.net>,
        "H. Peter Anvin" <hpa@...or.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Fengguang Wu <fengguang.wu@...el.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        David Ahern <dsahern@...il.com>, Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Wang Nan <wangnan0@...wei.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Borislav Petkov <bp@...en8.de>
Subject: Re: linker-tables v5 testing

On Wed, 30 Nov 2016 02:33:49 +0100
"Luis R. Rodriguez" <mcgrof@...nel.org> wrote:

> On Thu, Nov 24, 2016 at 08:18:40AM -0800, Guenter Roeck wrote:
> > Hi Luis,
> > 
> > On 11/23/2016 08:11 PM, Luis R. Rodriguez wrote:  
> > > Guenter,
> > > 
> > > I think I'm ready to start pushing a new patch set out for review.
> > > Before I do that -- can I trouble you for letting your test
> > > infrastructure hammer it? I'll only push out the patches for review
> > > based on this new set of changes once all tests come back OK for all
> > > architectures.
> > > 
> > > https://git.kernel.org/cgit/linux/kernel/git/mcgrof/linux-next.git/log/?h=20161117-linker-tables-v5
> > > 
> > > Fenguang & Guenter,
> > > 
> > > Any chance I can trouble you to enable the new driver:
> > > CONFIG_TEST_LINKTABLES=y on each kernel configuration as it will run a
> > > test driver which will WARN_ON() if it finds any errors.
> > >   
> > 
> > I see a number of compile failures as well as some crashes in your test driver.
> > Please have a look. http://kerneltests.org/builders, column 'testing'.
> >   
> 
> Thanks! I believe I have addressed most issues.. Any chance I can have you re-try with
> this new branch:
> 
> https://git.kernel.org/cgit/linux/kernel/git/mcgrof/linux-next.git/log/?h=20161117-linker-tables-v5-try2

Few minor things:

- Can module-common.lds be generated with standard cpp_lds_S?

- Breaking up the input section descriptions like that in the linker
  script is not what we want AFAIKS. It forces the linker to put them
  in different locations.

Broader issues:

- I still think calling these "sections" and "de facto Linux sections"
  etc. is a bit confusing, especially because assembler sections are
  also involved. Region, array, blob, anything. Then you get "section
  ranges" and "linker tables". Fundamentally all it is is a linear memory
  allocator for static data which is decentralized in the source code
  (as opposed to centralized which would just be `u8 mydata[size]`).

- It would be nice to just clearly separate the memory allocator function
  from the syntatic sugar on top. Actually I think if the memory allocation
  and access functions are clean enough, you don't need anything more. If
  we have an array of pointers and size, it's trivial C code to iterate over
  it. If it needs to have a set of LINKTABLE accessors over the top of it
  for this use case, then that would seem to be a failure of the underlying
  API, no?

- Is it really important to be able to add new allocators without modifying
  a central file for the linker script? Yes it's a benefit, but is it enough
  to justify the complexity?

Thanks,
Nick