Re: [PATCH v2] ld.so.8: Update "Hardware capabilities" section for glibc 2.31.

[Carlos O'Donell <carlos@redhat.com>]

On 6/10/20 2:00 AM, Michael Kerrisk (man-pages) wrote:
> Hi Carlos,
> 
> What's the status of this patch?

I'm currently rewriting the language of the section to split apart the
AT_PLATFORM and AT_HWCAP parts.

They each behave differently. AT_PLATFORM is a non-nested singular platform
directory that is searched with no fallback, and that needs to clarified
and called out. While AT_HWCAP is drastically different in behaviour.

When done we'll have two lists, and two explanations for the search paths
and their orders.

I'm doing this as part of the upstream review of this infrasturcture
because we're going to change the behaviour in an upcoming release. With
the changes in place we'll have a good place to say "... and now it's different."

In summary: Still working on it. Expect v3.

> On Tue, 2 Jun 2020 at 08:14, Florian Weimer <fweimer@redhat.com> wrote:
>>
>> * Carlos O'Donell:
>>
>>> +Care should be taken when packaging such application with a package manager,
>>> +particularly the scenario where an optimized library is being removed.  With
>>> +certain package managers, particularly rpm, the newer version of the
>>
>> Twice “particularly”.
>>
>>> +application is installed first, which means that for a period of time during
>>> +the upgrade all applications that use the library may start with a mixed set of
>>> +libraries e.g.  the old library from the feature-based search path, and new
>>
>> Commas arount e.g.?
>>
>>> +libraries from the upgrade. To avoid this scenario the new library version
>>> +should delete all known optimized libraries in the post-install phase.
>>
>> There is a different mechanism: Debian has patched glibc to disable
>> hwcap subdirectors if the file /etc/ld.so.nohwcap exists.
>>
>> You now list the AT_PLATFORM directories (determined by the kernel on
>> most architectures) along the regular hwcaps directories, although they
>> are handled somewhat differently.  For example, on s390x, if you have a
>> “z15” machine (as indicated by AT_PLATFORM), the “z13” subdirectory is
>> not selected.  ldconfig will add it to the cache, but it will not be
>> used at run time.  I'm not sure if your proposed description gives
>> readers the right idea what happens.
>>
>> Thanks,
>> Florian
>>
> 
> 
> --
> Michael Kerrisk
> Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
> Linux/UNIX System Programming Training: http://man7.org/training/
> 


-- 
Cheers,
Carlos.