linux-kernel - __initdata and struct dmi_system

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Date:	Fri, 05 Sep 2008 07:45:42 +0200
From:	Németh Márton <nm127@...email.hu>
To:	LKML <linux-kernel@...r.kernel.org>
CC:	linux-input@...r.kernel.org
Subject: __initdata and struct dmi_system_id?

Hi,

I have a question about how the __initdata sections are handled
under Linux. As far as I understand after the init function is
finished all the data from the __initdata section is freed. For
this reason all the data which are marked as __initdata should
be separated to a different section by the compiler.

I take for example the drivers/input/keyboards/atkbd.c where we
can see the following dmi_system_id structure:

static struct dmi_system_id atkbd_dmi_quirk_table[] __initdata = {
        {
                .ident = "Dell Latitude series",
                .matches = {
                        DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
                        DMI_MATCH(DMI_PRODUCT_NAME, "Latitude"),
                },
                .callback = atkbd_setup_fixup,
                .driver_data = atkbd_latitude_keymap_fixup,
        },
        {
                .ident = "HP 2133",
                .matches = {
                        DMI_MATCH(DMI_SYS_VENDOR, "Hewlett-Packard"),
                        DMI_MATCH(DMI_PRODUCT_NAME, "HP 2133"),
                },
                .callback = atkbd_setup_fixup,
                .driver_data = atkbd_hp_keymap_fixup,
        },
        { }
};

All these data should be separated to the section marked
with __initdata, so it can be freed. Let's see what happens
after compiling this with gcc 4.2.4. Here is the some part
of the output of "objdump -s drivers/input/keyboards/atkbd.o":

Contents of section .init.text:
 0000 558b4028 89e55da3 20000000 31c0c390  U.@(..]. ...1...
 0010 55b80000 000089e5 e8fcffff ffb95000  U.............P.
 0020 000031d2 b8200000 00e8fcff ffff5dc3  ..1.. ........].
Contents of section .rodata.str1.1:
 0000 256c750a 0025640a 00415420 53657420  %lu..%d..AT Set
 0010 32204578 74726120 6b657962 6f617264  2 Extra keyboard
 0020 00547261 6e736c61 74656400 52617700  .Translated.Raw.
 0030 41542025 73205365 74202564 206b6579  AT %s Set %d key
 0040 626f6172 64002573 2f696e70 75743000  board.%s/input0.
 0050 61746b62 64002628 2661746b 62642d3e  atkbd.&(&atkbd->
 0060 6576656e 745f776f 726b292d 3e776f72  event_work)->wor
 0070 6b002661 746b6264 2d3e6576 656e745f  k.&atkbd->event_
 0080 6d757465 78004143 4b004e41 4b007472  mutex.ACK.NAK.tr
 0090 616e736c 61746564 00726177 0072656c  anslated.raw.rel
 00a0 65617365 64007072 65737365 64006530  eased.pressed.e0
 00b0 00004465 6c6c204c 61746974 75646520  ..Dell Latitude
 00c0 73657269 65730044 656c6c20 496e632e  series.Dell Inc.
 00d0 004c6174 69747564 65004850 20323133  .Latitude.HP 213
 00e0 33004865 776c6574 742d5061 636b6172  3.Hewlett-Packar
 00f0 64004154 20616e64 2050532f 32206b65  d.AT and PS/2 ke
 0100 79626f61 72642064 72697665 72006578  yboard driver.ex
 0110 74726100 7363726f 6c6c0073 65740073  tra.scroll.set.s
 0120 6f667472 65706561 7400736f 66747261  oftrepeat.softra
 0130 77006572 725f636f 756e7400           w.err_count.

What I can see here is that some of the atkbd_dmi_quirk_table[]
content was stored into .init.text, but the strings like
"Dell Latitude series", "Dell Inc.", "Latitude", etc. were
combined to .rodata.str1.1 which also contain strings which
are NOT marked with __initdata. For example the string
"AT Set 2 Extra keyboard" is used in atkbd_set_device_attrs()
function thus the section .rodata.str1.1 cannot be freed after
the init is done.

Did I understand the situation correctly?
How is it possible to also allocate the strings which
belongs to struct dmi_system_id go to the section .init.text?

Also note that the drivers/input/keyboards/atkbd.c is only a
random example, drivers/leds/leds-clevo-mail.c has the same problem.

Regards,

	Márton Németh
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