[PATCHv3] powerpc: ABI change - add HWCAP/HWCAP2/platform info to TCB

[Joseph Myers]

On Wed, 23 Sep 2015, Peter Bergner wrote:

> On Wed, 2015-09-23 at 22:36 +0000, Joseph Myers wrote:
> > On Wed, 23 Sep 2015, Peter Bergner wrote:
> >> The idea is that applications will use the builtins supplied by GCC
> >> (and other compilers) and will not access this info directly.
> >> In GCC, my plan is to first add a configure test looking for the
> >> symbol and if it doesn't exist, then I'll make the builtins return
> > 
> > (Please make that configure test respect --with-glibc-version so that the 
> > results can be correct when a bootstrap compiler is configured without 
> > pre-existing glibc.)
> 
> So you want the --with-glibc-version option to take precedence over a
> configure time test that the __init_hwcapinfo (or whatever it ends up
> being called) exists?  Meaning we won't even do the configure time test
> if the user explicitly uses the --with-glibc-version option?

Yes.

I'm not clear on whether your configure test is meant to be in the gcc/ 
directory or in libgcc/.  In gcc/, it's not possible to do compile or link 
tests for the target at all - all you can do is examine headers for the 
target (which may or may not be available either).  The code to extract 
version numbers from headers, overridden by --with-glibc-version, already 
exists, so you could use GCC_GLIBC_VERSION_GTE_IFELSE in a configure test 
there.  In libgcc/, you can do compile tests but not link tests, but again 
it's probably simplest to use glibc_version_major and glibc_version_minor 
that configure.ac already computes taking due account of 
--with-glibc-version.

Given the inability to do link tests for the target, testing for a symbol 
isn't an option at all unless that symbol is mentioned in a header.

-- 
Joseph S. Myers
joseph@codesourcery.com