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Re: [PATCH] powerpc: New feature - HWCAP/HWCAP2 bits in the TCB
- From: Alan Modra <amodra at gmail dot com>
- To: OndÅej BÃlka <neleai at seznam dot cz>
- Cc: munroesj at linux dot vnet dot ibm dot com, Rich Felker <dalias at libc dot org>, libc-alpha at sourceware dot org
- Date: Tue, 7 Jul 2015 13:32:17 +0930
- Subject: Re: [PATCH] powerpc: New feature - HWCAP/HWCAP2 bits in the TCB
- Authentication-results: sourceware.org; auth=none
- References: <55760314 dot 6070601 at linux dot vnet dot ibm dot com> <20150609163835 dot GI17573 at brightrain dot aerifal dot cx> <1435777940 dot 7125 dot 132 dot camel at oc7878010663> <20150703195313 dot GB23898 at domone>
On Fri, Jul 03, 2015 at 09:53:13PM +0200, OndÅej BÃlka wrote:
> hwcap.h:
> int __hwcap __attribute__ ((visibility ("hidden"))) ;
>
> hwcap.c:
>
> #include <hwcap.h>
>
> // gcc needs to make this first constructor.
> extern int __global_hwcap;
> void __attribute__ ((constructor))
> set_hwcap ()
> {
> __hwcap = __global_hwcap;
> }
We considered using this scheme. In fact, I put forward the idea.
However, it was discarded as second best, due to the need to set up
GOT/TOC addressing on a variable access. Nothing beats Steve's single
instruction "ld r,-0x7068(r13)" to read hwcap.
--
Alan Modra
Australia Development Lab, IBM