Re: [Qemu-devel] [PATCH 2/3] kvm-userspace: kvmppc: fix hostlonbits detection when cross compiling v2

[Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>]

malc wrote:
> On Tue, 30 Sep 2008, ehrhardt@linux.vnet.ibm.com wrote:
>
>> From: Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>
>>
>> *update*
>> further debugging according to some requests revealed that 
>> ARCH_CFLAGS does
>> not contain all CFLAGS that might be needed, especially those 
>> supplied via
>> extra-cflags. Therefore people supplying things via extra-cflags 
>> instead of an
>> environment variable might have had issues.
>
> This part i don't get, there are few more checks before/after 
> hostlongbits where no CFLAGS are added to the $cc argument list. What
> makes hostlongbits selection "special"? Do people specify -m32/-m64 via
> --extra-cflags?
>
it was there to ensure availability of the needed include paths to reach 
wordsize.h.
But Hollis approach is much simpler, better and more reliable so never 
mind :-)

>>
>> A recent kvm merge with qemu brought code for 64bit power that broke 
>> cross
>> compilation. The issue is caused by configure trying to execute target
>> architecture binaries where configure is executed.
>
> Yes, i never thought about cross-compilation, my bad.
np, now it's fixed - thanks for quickly applying it.
>
>> I tried to change that detection so that it works with&without cross
>> compilation with only a small change and especially without an addtional
>> configure command line switch. Including the bits/wordsize.h header a 
>> platform
>> usually can check its wordsize and by doing that configure can check the
>> hostlongbits without executing the binary. Instead it now stops after
>> preprocessing stage which resolved the __WORDSIZE constant and retrieves
>> that value.
>>
>> I don't like my new check style, but it is at least less broken than 
>> before.
>> Another approach that was suggested was that qemu might end up needing
>> something like asm-offsets in the kernel to manage architecture sizes 
>> etc.
>> Comments and other approaches welcome.
>>
>
> I think Hollis Blanchard's method is sound,
>
> Thank you for bringing this up.
>


-- 

Grüsse / regards, 
Christian Ehrhardt
IBM Linux Technology Center, Open Virtualization