Re: [PATCH v2] powerpc: add sysconf support for cache geometries

["Tulio Magno Quites Machado Filho" <tuliom at linux dot vnet dot ibm dot com>]

Paul Clarke <pc@us.ibm.com> writes:

> There is currently no "cross-platform" (x86 and POWER) support for
> determining the cacheline size.
>
> This patch adds support to sysconf() to correctly report cacheline sizes
> based on the information in the auxilliary vector.
>
> Thus, using sysconf() is a cross-platform (x86 and POWER) solution for
> determining cacheline sizes.
>
> Support is added (on powerpc) for:
> _SC_LEVEL1_ICACHE_SIZE _SC_LEVEL1_ICACHE_ASSOC _SC_LEVEL1_ICACHE_LINESIZE
> _SC_LEVEL1_DCACHE_SIZE _SC_LEVEL1_DCACHE_ASSOC _SC_LEVEL1_DCACHE_LINESIZE
> _SC_LEVEL2_CACHE_SIZE  _SC_LEVEL2_CACHE_ASSOC  _SC_LEVEL2_CACHE_LINESIZE
> _SC_LEVEL3_CACHE_SIZE  _SC_LEVEL3_CACHE_ASSOC  _SC_LEVEL3_CACHE_LINESIZE
>
> 2017-04-28  Paul A. Clarke  <pc@us.ibm.com>
>
> 	* sysdeps/unix/sysv/linux/powerpc/sysconf.c: New file.
> 	Add powerpc-specific overrides for L1, L2, L3 CACHE_SIZEs,
> 	CACHE_ASSOCs, and CACHE_LINESIZEs, retrieving from auxv.
> 	* sysdeps/unix/sysv/linux/powerpc/test-powerpc-linux-sysconf.c:
> 	New file.  Invoke newly supported sysconf values for powerpc,
> 	and report results.  If none are supported, report so.
> 	* sysdeps/unix/sysv/linux/powerpc/Makefile (tests):  Add new test,
> 	tst-sysconf.

The patch looks good except for a small issue.

> diff --git a/sysdeps/unix/sysv/linux/powerpc/sysconf.c b/sysdeps/unix/sysv/linux/powerpc/sysconf.c
> new file mode 100644
> index 0000000..bb89933
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/powerpc/sysconf.c
> @@ -0,0 +1,96 @@
> +/* Get system-specific information at run-time.  Linux/powerpc version.
> +   Copyright (C) 2017 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <http://www.gnu.org/licenses/>.  */
> +
> +#include <errno.h>
> +#include <unistd.h>
> +#include <sys/auxv.h>
> +
> +static long linux_sysconf (int name);
> +
> +static long
> +auxv2sysconf (unsigned long type)
> +{
> +  long rc;
> +  rc = getauxval (type);

You need to bypass the PLT.  The problem is that neither getauxval()
nor __getauxval() provide this for you.

I'm sending a patch to treat this.

-- 
Tulio Magno