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

[Christophe Leroy]

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@xxxxxxxxxxxxxxxxxxx
> > > Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> > > Cc: linux-csky@xxxxxxxxxxxxxxx
> > > Cc: uclinux-h8-devel@xxxxxxxxxxxxxxxxxxxx
> > > Cc: linux-m68k@xxxxxxxxxxxxxxxxxxxx
> > > Cc: openrisc@xxxxxxxxxxxxxxxxxxxx
> > > Cc: linuxppc-dev@xxxxxxxxxxxxxxxx
> > > Cc: linux-riscv@xxxxxxxxxxxxxxxxxxx
> > > Cc: linux-sh@xxxxxxxxxxxxxxx
> > > Cc: linux-s390@xxxxxxxxxxxxxxx
> > > 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