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Re: [PATCH][aarch64] Fix hpwcap argument passed to ifunc resolvers
- From: Carlos O'Donell <carlos at redhat dot com>
- To: sellcey at cavium dot com, Szabolcs Nagy <szabolcs dot nagy at arm dot com>, libc-alpha <libc-alpha at sourceware dot org>
- Cc: nd at arm dot com
- Date: Thu, 31 Aug 2017 18:59:40 -0500
- Subject: Re: [PATCH][aarch64] Fix hpwcap argument passed to ifunc resolvers
- Authentication-results: sourceware.org; auth=none
- References: <1504132534.3182.4.camel@cavium.com> <59A8291E.2060205@arm.com> <1504195926.3182.20.camel@cavium.com>
On 08/31/2017 11:12 AM, Steve Ellcey wrote:
> On Thu, 2017-08-31 at 16:19 +0100, Szabolcs Nagy wrote:
>>
>> i'm not yet convinced that LD_HWCAP_MASK should be
>> applied to ifunc resolvers: glibc might be interested
>> in different hwcap flags than external users and the
>> important hwcaps mask has other effect in glibc that
>> i need to review.
>
> Personally, I like the idea that LD_HWCAP_MASK can affect ifunc
> resolvers. It gives users a single method to turn off some hardware
> capability across all libraries. I can see where finer grain control
> might also be useful but I think that in general we are going to have
> situations where a particular hardware capability is just not working
> the way it should and so we want to turn off its use everywhere in an
> executable.
I agree with Szabolcs.
The use of LD_HWCAP_MASK is a bit of mess in glibc.
Problems:
* We have one LD_HWCAP_MASK, but two HWCAPs e.g. AT_HWCAP, AT_HWCAP2.
* LD_HWCAP_MASK is used for multiple things:
* As a filter for ld.so.cache results.
* As a filter for multilib directory selection.
* We already have sysdeps/aarch64/dl-tunables.list to select
glibc.tune.cpu.type.
I'd just use the tunables.
--
Cheers,
Carlos.