Re: [PATCH v2 1/9] Add configure check to test if gcc supports attribute ifunc.

[Joseph Myers <joseph at codesourcery dot com>]

On Mon, 8 Aug 2016, Stefan Liebler wrote:

> This patch adds a configure check to test if gcc supports attribute ifunc.
> The support can either be enabled in <gcc-src>/gcc/config.gcc for one
> architecture in general by setting default_gnu_indirect_function variable to yes
> or by configuring gcc with --enable-gnu-indirect-function.
> 
> The next patch rewrites libc_ifunc macro to use gcc attribute ifunc instead
> of inline assembly to generate the IFUNC symbols due to false debuginfo.
> 
> If gcc does not support attribute ifunc and glibc is configured with
> --enable-multi-arch then configure will abort with an error message.
> If --enable-multi-arch is not given then configure will silently
> disable multi-arch support.

I'm concerned about requiring non-default configure options.  Various 
architectures support IFUNC in binutils and may have done so for a long 
time, but without the option being enabled in GCC by default.  There 
should be a much more detailed analysis of which architectures have IFUNC 
support in binutils, when it was added, and correspondingly, whether it's 
enabled by default in GCC for those architectures and, if so, when such 
enabling was added.

In any case, new compiler requirements must be documented in install.texi 
with INSTALL regenerated.  And should have appropriate NEWS entries as 
well.

-- 
Joseph S. Myers
joseph@codesourcery.com