Re: [PATCH] dlsym: Make RTLD_NEXT prefer default version definition [#BZ #14932]

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

On 22/05/2022 15:54, Fāng-ruì Sòng wrote:
> On Fri, May 20, 2022 at 7:22 AM Florian Weimer <fw@deneb.enyo.de> wrote:
>>
>> * Adhemerval Zanella via Libc-alpha:
>>
>>> On 20/05/2022 05:35, Fangrui Song via Libc-alpha wrote:
>>>> When the first object providing foo defines both foo@v1 and foo@@v2,
>>>> dlsym(RTLD_NEXT, "foo") returns foo@v1 while dlsym(RTLD_DEFAULT, "foo")
>>>> returns foo@@v2.  The issue is that RTLD_DEFAULT use the
>>>> DL_LOOKUP_RETURN_NEWEST flag while RTLD_NEXT doesn't.  Fix the RTLD_NEXT
>>>> branch to use DL_LOOKUP_RETURN_NEWEST.
>>>
>>> I am afraid we will need to add a compat dlsym for this change.
>>
>> My working theory is dlsym with RTLD_NEXT with a versioned symbol is
>> so buggy that this is not needed.  I want to understand the nature of
>> the bug, and plan to post a write-up.
> 
> Ok, thanks.
> 
> FWIW: I have verified that on FreeBSD 13.1, both dlsym(RTLD_NEXT,
> "foo") and dlsym(RTLD_DEFAULT, "foo") resolve to the default version
> definition, like what this patch does.

Right, I agree this is the most reasonable way to handle RTLD_NEXT with
versioned symbols specially because current semantic is to return the
*oldest* version with not apparent reason.  I guess that if caller wants
an old version it can use dlvsym with the appropriated version.

LGTM as well with Florian's remarks fixed.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>