Re: [patch] PR bootstrap/25672: Avoid CFLAGS in CFLAGS_FOR_TARGETS if cross-compiling

[Jeff Law <law at redhat dot com>]

On 03/09/15 16:22, Aldy Hernandez wrote:
> Hello gentlemen.
>
> The problem here is that we pick up the system's CFLAGS and pass it down
> to the target libraries.  This causes havoc when, for instance, CFLAGS
> is -march=x86-64 and the target is powerpc-linux.
>
> I don't see in what scenario the toplevel shell's CFLAGS would be of any
> use in the target libraries, so I've just avoided that code path
> altogether.
>
> Tested by doing a cross-build from x86-64 to ppc64-linux-gnu in a
> combined tree, and seeing if libgcc starts to build.  Previously we
> would fail while configuring GCC.  Now, gcc builds fine, and the target
> libraries start to build.
>
> OK for mainline?
>
> Aldy
>
> curr
>
>
> commit f2d130b93f334c5c680761553624964f87594adf
> Author: Aldy Hernandez<aldyh@redhat.com>
> Date:   Mon Mar 9 15:12:33 2015 -0700
>
>      	PR bootstrap/25672
>      	* configure.ac: Do not initialize CFLAGS_FOR_TARGET from CFLAGS if
>      	cross-compiling.  Similarly for CXX_FOR_TARGET.
>      	* configure: Regenerate.
I was wondering when someone would come across this oldie-but-goodie...

I'm sure someone, somewhere will complain that

make CFLAGS="whatever" isn't being passed down to the crossses as it has 
been for the last two decades.  And they'll be right.

But in the cross compiler case, I think it's reasonable to expect to 
have to use CFLAGS_FOR_TARGET so that we have separation between the 
host and target flags.  One could easily want to compile the host with 
one set of arguments and the target libraries with something completely 
different.

And note that the various .mt files already use the _FOR_TARGET macros 
to pass down additional flags rather than just CFLAGS or CXXFLAGS.



Are there any docs that need to change?  I don't recall any offhand, but 
if you could look prior to committing, it'd be appreciated.

OK for the trunk.

jeff