Re: [Patch][aarch64] Use IFUNCs to enable LSE instructions in libatomic on aarch64

[Steve Ellcey <sellcey@cavium.com>]

Ping.

Steve Ellcey
sellcey@cavium.com

On Thu, 2017-08-31 at 10:24 -0700, Steve Ellcey wrote:
> On Tue, 2017-08-29 at 12:25 +0100, Szabolcs Nagy wrote:
> > 
> >  
> > in glibc the hwcap is not used, because it has accesses to
> > cached dispatch info, but in libatomic using the hwcap
> > argument is the right way.
> Here is an updated version of the patch to allow aarch64 to use
> ifuncs
> in libatomic.
> 
> The main difference from the last patch is that the library does not
> access the hwcap value directly but accesses it through the ifunc
> resolver argument.  That means that we no longer need the
> init_cpu_revision static constructor to set a flag that the resolver
> checks, instead the resolver just does a comparision of its incoming
> argument with HWCAP_ATOMICS.
> 
> This did mean I had to change the prototype for the resolver
> functions
> in libatomic_i.h to have an argument, which is the way glibc calls
> them.  One complication of this is that the type of the argument can
> differ between platforms and ABIs so I added code to configure.tgt to
> set the type.  I used uint64_t for aarch64 and 'long unsigned int'
> for everything else.  That is not correct for all platforms but at 
> this point no other platforms access the argument so it should not
> matter.  If and when platforms do need to access it they can change
> the type if necessary.
> 
> Steve Ellcey
> sellcey@cavium.com
> 
> 
> 2017-08-31  Steve Ellcey  <sellcey@cavium.com>
> 
> 	* Makefile.am (ARCH_AARCH64_LINUX_LSE): Add IFUNC_OPTIONS and
> 	libatomic_la_LIBADD.
> 	* config/linux/aarch64/host-config.h: New file.
> 	* configure.ac (HWCAP_TYPE): Define.
> 	(AC_CHECK_HEADERS): Check for sys/auxv.h.
> 	(AC_CHECK_FUNCS): Check for getauxval.
> 	(ARCH_AARCH64_LINUX_LSE): New conditional for IFUNC builds.
> 	* configure.tgt (aarch64): Set AARCH and try_ifunc.
> 	(aarch64*-*-linux*) Update config_path.
> 	(aarch64*-*-linux*) Set HWCAP_TYPE.
> 	* libatomic_i.h (GEN_SELECTOR): Add "HWCAP_TYPE hwcap"
> argument.
> 	* Makefile.in: Regenerate.
> 	* auto-config.h.in: Regenerate.
> 	* configure: Regenerate.
>