linux-kernel - Re: [PATCH] lib/xz: Fix powerpc build with KERNEL

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Date:   Wed, 19 Sep 2018 08:52:37 +0200
From:   Christophe LEROY <christophe.leroy@....fr>
To:     Oliver <oohall@...il.com>
Cc:     Joel Stanley <joel@....id.au>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] lib/xz: Fix powerpc build with KERNEL_XZ



Le 19/09/2018 à 08:44, Oliver a écrit :
> On Wed, Sep 19, 2018 at 3:52 PM, Christophe LEROY
> <christophe.leroy@....fr> wrote:
>>
>>
>> Le 19/09/2018 à 01:07, Joel Stanley a écrit :
>>>
>>> This partially reverts faa16bc404d72a5 ("lib: Use existing define with
>>> polynomial").
>>>
>>> The cleanup added a dependency on include/linux, which broke the PowerPC
>>> boot wrapper/decompresser when KERNEL_XZ is enabled:
>>>
>>>     BOOTCC  arch/powerpc/boot/decompress.o
>>>    In file included from
>>> arch/powerpc/boot/../../../lib/decompress_unxz.c:233,
>>>                    from arch/powerpc/boot/decompress.c:42:
>>>    arch/powerpc/boot/../../../lib/xz/xz_crc32.c:18:10: fatal error:
>>>    linux/crc32poly.h: No such file or directory
>>>     #include <linux/crc32poly.h>
>>>              ^~~~~~~~~~~~~~~~~~~
>>>
>>> The powerpc decompressor is a hairy corner of the kernel. Even while
>>> building
>>> a 64-bit kernel it needs to build a 32-bit binary and therefore avoid
>>> including
>>> files from include/linux.
>>>
>>> Fixes: faa16bc404d7 ("lib: Use existing define with polynomial")
>>> Signed-off-by: Joel Stanley <joel@....id.au>
>>> ---
>>> We need to clean up the powerpc boot decompresser but that work will be
>>> more involved than we would include in a late -rc. Please consider
>>> merging this fix for 4.19. Thanks!
>>>
>>>    lib/xz/xz_crc32.c | 3 +--
>>>    1 file changed, 1 insertion(+), 2 deletions(-)
>>>
>>> diff --git a/lib/xz/xz_crc32.c b/lib/xz/xz_crc32.c
>>> index 25a5d87e2e4c..34532d14fd4c 100644
>>> --- a/lib/xz/xz_crc32.c
>>> +++ b/lib/xz/xz_crc32.c
>>> @@ -15,7 +15,6 @@
>>>     * but they are bigger and use more memory for the lookup table.
>>>     */
>>>    -#include <linux/crc32poly.h>
>>>    #include "xz_private.h"
>>>      /*
>>> @@ -30,7 +29,7 @@ STATIC_RW_DATA uint32_t xz_crc32_table[256];
>>>      XZ_EXTERN void xz_crc32_init(void)
>>>    {
>>> -       const uint32_t poly = CRC32_POLY_LE;
>>> +       const uint32_t poly = 0xEDB88320;
>>
>>
>> Maybe avoid capital letters ?
>>
>> What about adding something like the following in xz_private.h instead:
>>
>> #define CRC32_POLY_LE 0xedb88320
> 
> The problem is that it's pulling in linux/crc32poly.h. To support old
> systems with a 32bit Open Firmware we boot wrapper we build the boot
> wrapper as a 32bit ELF even for a 64 bit kernel. The headers generated
> by Kbuild are only valid for the 64bit kernel so we have to avoid
> pulling them into the boot wrapper.

Yes I understood, hence my proposal to redefine CRC32_POLY_LE in 
xz_private.h instead of including linux/crc32poly.h

It avoids modifying the C code.

Christophe

> 
>> Christophe
>>
>>>          uint32_t i;
>>>          uint32_t j;
>>>
>>