Re: Support for out-of-tree build

[Rich Felker <dalias@libc.org>]

On Tue, Nov 17, 2015 at 10:15:29PM +0000, Petr Hosek wrote:
> Absolutely, that's probably the simplest solution in the sense that it
> avoids using additional .mk/.sub files or complicated build-time logic.
> 
> If that's the solution we all agree on, I'd be happy to implement this as a
> separate patch and then rebase the out-of-tree build patch on top of that.

The only concern I'm aware of for this is interaction of the CFI
generation scripts with preprocessed asm. They might need to be
updated to be able to handle it safely. At present x86[_64] has no
need for preprocessing anyway so it's not a pressing issue, but we
should probably think through the consequences and make sure we don't
get into another situation that's hard to get out of.

One idea that came up on irc was that we could shift to doing more of
the arch asm with inline asm in C rather than asm source files. This
would eliminate most of the need for CFI generation and would yield
better LTO results. There are a few files for which this can't be
done, however, and I'm not sure everyone likes the idea in principle,
though I haven't seen any strong technical reasons not to do it.

Rich