linux-kernel - Re: [RFC v1 4/8] x86/init: add linker table support

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Date:	Thu, 21 Jan 2016 16:19:48 -0800
From:	"Luis R. Rodriguez" <mcgrof@...not-panic.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Roger Pau Monné <roger.pau@...rix.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Andy Lutomirski <luto@...capital.net>,
	Michael Brown <mcb30@...e.org>,
	Juergen Gross <jgross@...e.com>,
	Jan Beulich <JBeulich@...e.com>, joro@...tes.org,
	Andrey Ryabinin <ryabinin.a.a@...il.com>,
	long.wanglong@...wei.com, qiuxishi@...wei.com,
	aryabinin@...tuozzo.com,
	Mauro Carvalho Chehab <mchehab@....samsung.com>,
	Valentin Rothberg <valentinrothberg@...il.com>,
	Peter Senna Tschudin <peter.senna@...il.com>,
	X86 ML <x86@...nel.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Luis R. Rodriguez" <mcgrof@...e.com>
Subject: Re: [RFC v1 4/8] x86/init: add linker table support

On Thu, Jan 21, 2016 at 11:52 AM, H. Peter Anvin <hpa@...or.com> wrote:
> On 01/21/16 11:50, H. Peter Anvin wrote:
>>
>> Right... we already do that.
>>
>> I don't even think you need to initialize any tables.  At least on i386,
>> we have to do this in assembly code.  However, it is just a simple table
>> walk.  :)
>>
>
> It might make more sense to make subarch its own table, though, although
> I haven't looked at your code in enough detail to say.

The gist of it:

void x86_init_fn_early_init() {
  for_each_table_entry(init_fn, X86_INIT_FNS) {
     if supported subarc
      init_fn->early_init();
}

void x86_init_fn_setup_arch() {
  for_each_table_entry(init_fn, X86_INIT_FNS) {
     if supported subarc
      init_fn->setup_archt();
}

Right now the code defines just an init routine at the stage for
x86_64_start_reservations(), we call the callback early_init(), ie
setup_arch() doesn't exist yet. Since certain routines can run on
either Xen or bare-metal we allow a bitwise OR for the subarch as a
bitmask. I'll think a bit more about how to use subarch for a table,
but can't fit it yet. I'd like to later revise kfree'ing unused
sections, and a table per subarch might be nice for that, but
otherwise this flow seems easy to follow, so if we can kfree sections
within a table we could still accomplish that later.

  Luis