[PATCH v9 3/5] Fix assert during static startup (BZ 33326)

[Adhemerval Zanella Netto]

On 11/06/26 15:39, Adhemerval Zanella Netto wrote:
> 
> 
> On 08/06/26 11:26, Adhemerval Zanella Netto wrote:
>>
>>
>> On 08/06/26 09:14, Adhemerval Zanella Netto wrote:
>>>
>>>
>>> On 08/06/26 07:46, Florian Weimer wrote:
>>>> * Adhemerval Zanella:
>>>>
>>>> I think the general issue is not right: During startup, we should not
>>>> use mmap to allocate the backing store.  We can preserve the assert
>>>> message and file name by copying them to on-stack buffer.  As no user
>>>> code should be running at this point, we do not need to be prepared for
>>>> arbitrarily-long assert messages (but we still should have a length
>>>> check, of course).
>>>>
>>>> Can we redirect to a different assert implementation during early
>>>> startup?
>>>
>>> I think I can reinstate the assert wrapper [1]. I kept the assert used 
>>> simplify the the implementation and use the same code path.  We can use
>>> a stack allocated buffer and cap the message string, for glibc own usage we
>>> would know when we need to increase it.
>>>
>>> But it also raises the question whether we do copy the buffer in this case,
>>> this assert will be only used during process startup and it would be triggered
>>> in cases that can be considered glibc issues.
>>>
>>> [1] https://sourceware.org/pipermail/libc-alpha/2026-March/176039.html
>> It turned out that for the rtld it is already done by elf/dl-minimal.c
>> __assert_fail/__assert_perror_fail which only calls _dl_fatal_printf instead
>> of __libc_assert_fail (which in turn calls __libc_message_impl).
>>
>> Now changing this to *static-pie* means making static-pie act more like
>> rtld and less lime a static binary: we will need to add some logic on
>> the libc __libc_message_impl to handle static-pie and/or adding some
>> mechanism to override assert (similar how it is done for rtld). I don't
>> think either worth the trouble.
> 
> I am planning to send a new version with your remarks fixes, do you still have
> reservations for this assert on static-pie Florian? This patch does not really
> change any semantic, loader still uses the minimal implementation.

Florian, do you still have reservation about this mmap usage for static-pie?
I would like to send a new version with your other comments addressed.