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Date:   Mon, 6 Apr 2020 09:43:21 -0700
From:   Fangrui Song <maskray@google.com>
To:     Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc:     YunQiang Su <wzssyqa@gmail.com>,
        "Maciej W. Rozycki" <macro@linux-mips.org>,
        linux-mips <linux-mips@vger.kernel.org>,
        Nathan Chancellor <natechancellor@gmail.com>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] MIPS: malta: Set load address for 32bit kernel correctly
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On 2020-04-06, Jiaxun Yang wrote:
>
>
>于 2020年4月6日 GMT+08:00 下午6:57:18, YunQiang Su <wzssyqa@gmail.com> 写到:
>>Maciej W. Rozycki <macro@linux-mips.org> 于2020年4月6日周一 上午1:23写道：
>>>
>>> On Mon, 6 Apr 2020, Jiaxun Yang wrote:
>>>
>>> > > Given the description above I think it should be done uniformly
>>and
>>> > >automatically across all platforms by trimming the address
>>supplied
>>> > >with
>>> > >$(load-y) to low 8 digits in a single place, that is at the place
>>where
>>> > >
>>> > >the variable is consumed.  This will reduce clutter across
>>Makefile
>>> > >fragments, avoid inconsistencies and extra work to handle
>>individual
>>> > >platforms as the problem is triggered over and over again, and
>>limit
>>> > >the
>>> > >risk of mistakes.
>>> >
>>> > I was intended to do like this but failed to find a proper way.
>>> >
>>> > Makefile isn't designed for any kind of calculation.
>>> > And shell variables are 64-bit signed so it can't hold such a huge
>>variable.
>>> >
>>> > Just wish somebody can give me a way to do like:
>>> >
>>> > ifndef CONFIG_64BIT
>>> > load-y = $(load-y) & 0xffffffff
>>> > endif
>>>
>>>  Use the usual shell tools like `sed', `cut', `awk', or whatever we
>>use in
>>
>>perl may be the easiest to use tool here.
>>
>>ifndef CONFIG_64BIT
>>  load-y := $(shell $(PERL) -e 'print $(load-y) & 0xffffffff')
>>endif
>>
>>Note that it is `:=' instead of '='.
>
>It seems like perl is not one of kernel's build dependencies.[1]
>I'm comsidering a alternative solution,
>write a small hostprog in C to deal with that.
>
>Thanks.
>
>[1]: https://www.kernel.org/doc/html/v5.6/process/changes.html

load-y := 0xffffffff80100000
load-y := 0x$(shell echo "$(load-y)" | rev | head -c 8 | rev)

>>
>>> the kernel build already for other purposes.  There's no need to do
>>any
>>> actual calculation here to extract the last 8 characters (and the
>>leading
>>> `0x' prefix).  At worst you can write a small C program, compile it
>>with
>>> the build system compiler and run, as we already do for some stuff.
>>>
>>>   Maciej
>
>-- 
>Jiaxun Yang