Re: Issue in man page PR_SET_SECUREBITS.2const

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

On 8/25/25 3:41 PM, Alejandro Colomar wrote:
> Hi Carlos,
> 
> On Mon, Aug 25, 2025 at 01:52:03PM -0400, Carlos O'Donell wrote:
>> On 8/24/25 3:21 PM, Alejandro Colomar wrote:
>>> Hi Helge,
>>>
>>>> Subject: Re: Issue in man page PR_SET_SECUREBITS.2const
>>>
>>> You probably meant PR_SET_THP_DISABLE.2const.  The text you quoted is
>>> there:
>>>
>>> 	$ grep -rn THP.disable
>>> 	man/man2const/PR_SET_THP_DISABLE.2const:9:set the state of the "THP disable" flag for the calling thread
>>> 	man/man2const/PR_SET_THP_DISABLE.2const:21:Set the state of the "THP disable" flag for the calling thread.
>>> 	man/man2const/PR_SET_THP_DISABLE.2const:32:The setting of the "THP disable" flag is inherited by a child created via
>>> 	man/man2const/PR_GET_THP_DISABLE.2const:9:get the state of the "THP disable" flag for the calling thread
>>> 	man/man2const/PR_GET_THP_DISABLE.2const:22:the "THP disable" flag for the calling thread:
>>>
>>> On Sun, Aug 24, 2025 at 02:48:48PM +0000, Helge Kreutzmann wrote:
>>>> Without further ado, the following was found:
>>>>
>>>> Issue:    malloc → B<malloc>(3) ?
>>>
>>> Maybe, but we should probably add a reference to malloc_hook(3) instead?
>>
>> In a modern system you care about malloc not malloc_hook.
>>
>> The hooks have been removed and glibc has directly integrated THP usage in malloc instead.
>>
>> https://sourceware.org/glibc/manual/2.42/html_node/Memory-Allocation-Tunables.html
> 
> Thanks!  Do we need a more thorough rewrite of this page is needed?
> Or just replace malloc by malloc(3)?

Yes, the existing text is only correct for < 2.34 glibc system.

A > 2.34 system has THP support with the tunable to support THP (for legacy libhugetlbfs users).

And a glibc == 2.34 system lacks this feature and doesn't support such hook + interposer deployments.

The quickest fix is to reference malloc(3) for now.

-- 
Cheers,
Carlos.