Re: [PATCH] ARM: tegra: paz00: fix __initdata placement

Dmitry Torokhov
2017-01-24T18:27:01Z

On Mon, Jan 23, 2017 at 05:24:28PM +0100, Thierry Reding wrote:
> On Mon, Jan 23, 2017 at 11:04:22AM +0100, Marc Dietrich wrote:
> > Hello Dmitry,
> >
> > Am Sonntag, 22. Januar 2017, 23:43:47 CET schrieb Dmitry Torokhov:
> > > To have expected effect the __initdata attribute should go after variable
> > > name and before initializer.`
> > >
> > > Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
> > > ---
> > > arch/arm/mach-tegra/board-paz00.c | 2 +-
> > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/arch/arm/mach-tegra/board-paz00.c
> > > b/arch/arm/mach-tegra/board-paz00.c index 7478f6fb3664..ea6bff404161 100644
> > > --- a/arch/arm/mach-tegra/board-paz00.c
> > > +++ b/arch/arm/mach-tegra/board-paz00.c
> > > @@ -23,7 +23,7 @@
> > >
> > > #include "board.h"
> > >
> > > -static struct property_entry __initdata wifi_rfkill_prop[] = {
> > > +static struct property_entry wifi_rfkill_prop[] __initdata = {
> > > PROPERTY_ENTRY_STRING("name", "wifi_rfkill"),
> > > PROPERTY_ENTRY_STRING("type", "wlan"),
> > > { },
> >
> > you are right according to the documentation, but objdump -s always shows that
> > it gets put into the .rodata section. So this patch has no effect, because
> > result is always same (and wrong). It's also possible that I'm doing something
> > wrong :-) Btw, there are hundreds of such __initdata misplacement in the
> > kernel.
>
> Hmm... I get this:
>
> $ objdump -t build/tegra20/arch/arm/mach-tegra/board-paz00.o
>
> build/tegra20/arch/arm/mach-tegra/board-paz00.o: file format
> elf32-little
>
> SYMBOL TABLE:
> 00000000 l df *ABS* 00000000 board-paz00.c
> 00000000 l d .text 00000000 .text
> 00000000 l d .data 00000000 .data
> 00000000 l d .bss 00000000 .bss
> 00000000 l d .init.text 00000000 .init.text
> 00000000 l .init.text 00000000 $a
> 00000000 l .data 00000000 .LANCHOR1
> 00000000 l .init.data 00000000 .LANCHOR0
> 00000000 l d .ARM.extab.init.text 00000000 .ARM.extab.init.text
> 00000000 l d .ARM.exidx.init.text 00000000 .ARM.exidx.init.text
> 00000000 l .ARM.exidx.init.text 00000000 $d
> 00000000 l .data 00000000 $d
> 00000000 l O .data 000001c8 wifi_rfkill_device
> 000001c8 l O .data 00000048 wifi_gpio_lookup
> 00000000 l d .rodata.str1.4 00000000 .rodata.str1.4
> 00000000 l .rodata.str1.4 00000000 $d
> 00000000 l d .init.data 00000000 .init.data
> 00000000 l .init.data 00000000 $d
> 00000000 l O .init.data 00000048 wifi_rfkill_prop
> 00000000 l d .debug_frame 00000000 .debug_frame
> 00000010 l .debug_frame 00000000 $d
> 00000000 l d .debug_info 00000000 .debug_info
> 00000000 l d .debug_abbrev 00000000 .debug_abbrev
> 00000000 l d .debug_aranges 00000000 .debug_aranges
> 00000000 l d .debug_ranges 00000000 .debug_ranges
> 00000000 l d .debug_line 00000000 .debug_line
> 00000000 l d .debug_str 00000000 .debug_str
> 00000000 l d .note.GNU-stack 00000000 .note.GNU-stack
> 00000000 l d .comment 00000000 .comment
> 00000000 l d .ARM.attributes 00000000 .ARM.attributes
> 00000000 g F .init.text 00000030 tegra_paz00_wifikill_init
> 00000000 *UND* 00000000 platform_device_add_properties
> 00000000 *UND* 00000000 gpiod_add_lookup_table
> 00000000 *UND* 00000000 platform_device_register
> 00000000 *UND* 00000000 __aeabi_unwind_cpp_pr0
>
> So it correctly ends up in .init.data for me. And it does so with or
> without the patch. GCCs documentation doesn't seem to say where exactly
> these attributes need to be put, though the examples given all have the
> attribute right before the =.
>
> Oh... interestingly checkpatch does seem to have a check for this now,
> and it does recommend that __initdata be placed after wifi_rfkill_prop,
> so I'm going to apply this.

Ah, so I mis-remembered the rules and it seems that it does not really
matter if __initdata goes before or after variable name, it can't go
between "struct" and its name. From that checkpatch change introducing
the check:

static struct __initdata samsung_pll_clock exynos4_plls[nr_plls] = {

does NOT put exynos4_plls in the .initdata section. The __initdata marker
can be virtually anywhere on the line, EXCEPT right after "struct". The
preferred location is before the "=" sign if there is one, or before the
trailing ";" otherwise.

so if you are applying it you might want to change the wording as to the
effect of "making checkpatch happy" which wasn't my intention, but was
the outcome ;)

Thanks.

--
Dmitry