linux-kernel - Re: [PATCH v2 00/15] init_mm: cleanup ARCH's text/data/brk setup code

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Date:   Mon, 7 Jun 2021 07:48:54 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Kefeng Wang <wangkefeng.wang@...wei.com>,
        Mike Rapoport <rppt@...nel.org>
Cc:     uclinux-h8-devel@...ts.sourceforge.jp, linux-s390@...r.kernel.org,
        linux-sh@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-csky@...r.kernel.org, linux-mm@...ck.org,
        linux-m68k@...ts.linux-m68k.org, openrisc@...ts.librecores.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-snps-arc@...ts.infradead.org, linuxppc-dev@...ts.ozlabs.org,
        linux-riscv@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 00/15] init_mm: cleanup ARCH's text/data/brk setup code

Hi Kefeng,

Le 07/06/2021 à 02:55, Kefeng Wang a écrit :
> 
> On 2021/6/7 5:29, Mike Rapoport wrote:
>> Hello Kefeng,
>>
>> On Fri, Jun 04, 2021 at 03:06:18PM +0800, Kefeng Wang wrote:
>>> Add setup_initial_init_mm() helper, then use it
>>> to cleanup the text, data and brk setup code.
>>>
>>> v2:
>>> - change argument from "char *" to "void *" setup_initial_init_mm()
>>>    suggested by Geert Uytterhoeven
>>> - use NULL instead of (void *)0 on h8300 and m68k
>>> - collect ACKs
>>>
>>> Cc: linux-snps-arc@...ts.infradead.org
>>> Cc: linux-arm-kernel@...ts.infradead.org
>>> Cc: linux-csky@...r.kernel.org
>>> Cc: uclinux-h8-devel@...ts.sourceforge.jp
>>> Cc: linux-m68k@...ts.linux-m68k.org
>>> Cc: openrisc@...ts.librecores.org
>>> Cc: linuxppc-dev@...ts.ozlabs.org
>>> Cc: linux-riscv@...ts.infradead.org
>>> Cc: linux-sh@...r.kernel.org
>>> Cc: linux-s390@...r.kernel.org
>>> Kefeng Wang (15):
>>>    mm: add setup_initial_init_mm() helper
>>>    arc: convert to setup_initial_init_mm()
>>>    arm: convert to setup_initial_init_mm()
>>>    arm64: convert to setup_initial_init_mm()
>>>    csky: convert to setup_initial_init_mm()
>>>    h8300: convert to setup_initial_init_mm()
>>>    m68k: convert to setup_initial_init_mm()
>>>    nds32: convert to setup_initial_init_mm()
>>>    nios2: convert to setup_initial_init_mm()
>>>    openrisc: convert to setup_initial_init_mm()
>>>    powerpc: convert to setup_initial_init_mm()
>>>    riscv: convert to setup_initial_init_mm()
>>>    s390: convert to setup_initial_init_mm()
>>>    sh: convert to setup_initial_init_mm()
>>>    x86: convert to setup_initial_init_mm()
>> I might be missing something, but AFAIU the init_mm.start_code and other
>> fields are not used really early so the new setup_initial_init_mm()
>> function can be called in the generic code outside setup_arch(), e.g in
>> mm_init().
> 
> Hi Mike， each architecture has their own value, not the same, eg m68K and
> 
> h8300, also the name of the text/code/brk is different in some arch, so I keep
> 
> unchanged.

What you could do is to define a __weak function that architectures can override and call that 
function from mm_init() as suggested by Mike,

Something like:

void __weak setup_initial_init_mm(void)
{
	init_mm.start_code = (unsigned long)_stext;
	init_mm.end_code = (unsigned long)_etext;
	init_mm.end_data = (unsigned long)_edata;
	init_mm.brk = (unsigned long)_end;
}

Then only the few architecture that are different would override it.

I see a few archictectures are usigne PAGE_OFFSET to set .start_code, but it is likely that this is 
equivalent to _stext.

Christophe