Re: [PATCH 1/2] arm: Implement memcpy ifunc selection in C

[Joseph Myers <joseph at codesourcery dot com>]

On Fri, 6 Oct 2017, Adhemerval Zanella wrote:

> This patch refactor ARM memcpy ifunc selector to a C implementation.
> No functional change is expected, including ifunc resolution rules.
> 
> To avoid build issues with mainline GCC which set no default gnu
> indirect function support for ARM (--enable-gnu-indirect-function)
> two fixes are added:
> 
>   1. The new macro arm_libc_ifunc_hidden_def is redefined using
>      direct asm assembly directives instead of function attributes.
>      This avoid the incompatbile types for a symbol and its alias.
> 
>   2. A new macro NO_MEM_INTERAL_SYM_HACKS is added on symbol-hacks
>      and defined on arm ifunc objects.  It avoids the symbol
>      definition loop because compiler might emit the hacks for first
>      fix before the ifunc function definition itself.

As a general principle, I don't think we should be checking in workarounds 
for defects in unreleased GCC versions (this is not specific to this 
particular issue - it means more generally that if you see a warning 
building with mainline GCC, you need to consider whether that warning is 
buggy before applying glibc changes to avoid the warning).

That is, we should fix the default in GCC mainline and then propose glibc 
changes that do not involve such workarounds.  (Arguably the default 
should be to support the attribute for all architectures, to avoid future 
issues when new architectures gain binutils support for IFUNCs after the 
GCC 8 release.)

-- 
Joseph S. Myers
joseph@codesourcery.com