Re: Inheriting CFLAGS

[Jerome Brown <guruswami@orcon.net.nz>]

No, I do not have those lines in my Rules.mk file. It was downloaded 
this morning using the ebuild, so was the xen-2.0.tgz file from 
sourceforge. If I add -nopie to the CFLAGS in Rules.mk file xen will 
compile fine, however if I add -nopie to my environment CFLAGS it does 
not get picked up by the xen build script. Therefore I can compile and 
install it, but it takes manual intervention, which defeats the idea of 
using an ebuild :)

I am not looking of inheriting CFLAGS into the kernel build process - I 
agree that it is bad. However I am unable to build Xen-2.0 itself with 
my compiler. Unfortunately, unlike with GCC 3.4, it doesn't compile a 
non-SSP/PIE version of gcc to use. (I'm running gcc 3.3.4)

Keir Fraser wrote:
>>>I am attempting to install Xen-2.0 using the Gentoo Ebuilds written by Philip
>>>Taylor, and have run into the same problem as A Streecar Named with needing to
>>>implement the -nopie flag.
>>
>>strange, I didn't have to do it (using ebuilds from 
>>http://bugs.gentoo.org/show_bug.cgi?id=70161)
> 
> 
> Yes, I did wonder about this.
> 
> Can you take a look in xen/arch/x86/Rules.mk and see if you have the
> lines:
>  # Disable PIE/SSP if GCC supports them. They can break us.
>  CFLAGS  += $(call test-gcc-flag,-nopie)
>  CFLAGS  += $(call test-gcc-flag,-fno-stack-protector)
>  CFLAGS  += $(call test-gcc-flag,-fno-stack-protector-all)
> 
> If so then you have a *very* up-to-date tree. :-) I recently checked
> in a build fix that would disable PIE/SSP iff they are supported by
> GCC. 
> 
> If not then I'm confused!
> 
> 
>>>Is it possible to have Xen inherit these CFLAGS as a base, and then modify
>>>them as required? Part of the enthusiasm over Gentoo is the ability to
>>>customise and optimise the applications.
>>
>>If you're talking about kernel, I don't think it's a good idea. None of 
>>the packages under sys-kernel inherits CFLAGS from Portage's 
>>/etc/make.conf.
> 
> 
> Yeah, it's a bad idea! Kernels are very sensitive to compile flags
> -- both Xen and Linux use a wide range of GCC features and frequently
> use inline assembler, so the code is fragile when flags are changed
> from what we developers use. Allowing CFLAGS to be modified would be
> giving users a loaded gun. :-)
> 
>  -- Keir
> 
> 
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