linux-kernel - Re: [PATCH] MIPS: malta: Set load address for 32bit kernel correctly

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Date:   Mon, 06 Apr 2020 00:53:26 +0800
From:   Jiaxun Yang <jiaxun.yang@...goat.com>
To:     "Maciej W. Rozycki" <macro@...ux-mips.org>
CC:     linux-mips@...r.kernel.org, Fangrui Song <maskray@...gle.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] MIPS: malta: Set load address for 32bit kernel correctly



于 2020年4月6日 GMT+08:00 上午12:47:29, "Maciej W. Rozycki" <macro@...ux-mips.org> 写到:
>On Sun, 5 Apr 2020, Jiaxun Yang wrote:
>
>> LLD failed to link vmlinux with 64bit load address for 32bit ELF
>> while bfd will strip 64bit address into 32bit silently.
>> To fix LLD build, we should supply a 32bit load address for 32bit
>> kernel.
>[...]
>> diff --git a/arch/mips/mti-malta/Platform
>b/arch/mips/mti-malta/Platform
>> index 2cc72c9b38e3..f9b49cba1764 100644
>> --- a/arch/mips/mti-malta/Platform
>> +++ b/arch/mips/mti-malta/Platform
>> @@ -6,6 +6,10 @@ cflags-$(CONFIG_MIPS_MALTA)	+=
>-I$(srctree)/arch/mips/include/asm/mach-malta
>>  ifdef CONFIG_KVM_GUEST
>>      load-$(CONFIG_MIPS_MALTA)	+= 0x0000000040100000
>>  else
>> +ifdef CONFIG_64BIT
>>      load-$(CONFIG_MIPS_MALTA)	+= 0xffffffff80100000
>> +else
>> +    load-$(CONFIG_MIPS_MALTA)	+= 0x80100000
>
> Given the description above I think it should be done uniformly and 
>automatically across all platforms by trimming the address supplied
>with 
>$(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

In makefiles.

Thanks.
>
>Some error checking might be doable for verifying that the 64-bit
>address 
>truncated is a sign-extended 32-bit value, but that perhaps would be an
>
>overkill as certainly any 64-bit system that sets the load address to
>be 
>outside the sign-extended 32-bit address range does not support a
>!64BIT 
>configuration anyway.
>
>  Maciej

-- 
Jiaxun Yang