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Re: [Bug-readline] [PATCH] Enable visibility annotations


From: Yury Gribov
Subject: Re: [Bug-readline] [PATCH] Enable visibility annotations
Date: Fri, 22 Apr 2016 18:09:54 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0

On 04/22/2016 05:51 PM, Pedro Alves wrote:
On 04/19/2016 06:45 PM, Chet Ramey wrote:
On 4/18/16 3:19 AM, Pedro Alves wrote:

I've also fixed an issue in script and added fixed patch which
additionally visualizes _rl_horizontal_scroll_mode (required by trunk gdb).

I ran this now and got:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Symbols which may be used and are missing in new libreadline:
rl_complete_with_tilde_expansion
_rl_mark_modified_lines

These two correspond to bindable readline variables.  The former retains
its rl_ prefix for backwards (and historical) compatibility.

I think the visibility patches raise a question that should
be considered:

Does readline still want to keep these historical "rl_" symbols,
even those that we hadn't found any program is using (at
least yet) ?

Because I think that if we hide them with private visibility,
then that effectively is the same thing as removing them
for dynamic links.  However, if we don't remove them, then we
end up with the inconsistency where a link with dynamic
libreadline.so fails, while a link with static libreadline.a succeeds.

It seems to me that readline should either:

  - completely delete old undocumented backwards compatibility symbols,
    or,

  - mark them public.

Leaving them defined, but marked private leads to the dynamic
vs static inconsistency mentioned above.

I'm afraid this inconsistency is inevitable. Static libs are mere archives and do not have any mechanism for visibility control. They'll always be leaking internal symbols and there is not workaround for that (well, except for marking symbols static or removing them alltogether which is obviously not always possible).

-Y




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