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Subject: Re: Calling functions through a pointer of incorrect type
To: Joseph Myers <joseph@codesourcery.com>
References: <56F10E3B.60300@redhat.com>
 <alpine.DEB.2.10.1603221912110.30564@digraph.polyomino.org.uk>
Cc: GNU C Library <libc-alpha@sourceware.org>
From: Florian Weimer <fweimer@redhat.com>
Message-ID: <56F1AA47.6040509@redhat.com>
Date: Tue, 22 Mar 2016 20:25:00 -0000
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On 03/22/2016 08:14 PM, Joseph Myers wrote:
> On Tue, 22 Mar 2016, Florian Weimer wrote:
> 
>> Just a sanity check: It is no longer acceptable glibc coding style to
>> call functions through mismatching pointer types.  Correct?
> 
> I think more specific examples would help so we can see if there are 
> cleaner approaches that generate the same code.  (For example, it's 
> deliberate that in some places functions with incompatible C types but 
> compatible ABIs are aliased to each other.)

I saw this in getaddrinfo:

  if (fct == NULL)
    /* We are cheating here.  The gethostbyname2_r
       function does not have the same interface as
       gethostbyname3_r but the extra arguments the
       latter takes are added at the end.  So the
       gethostbyname2_r code will just ignore them.  */
    fct = __nss_lookup_function (nip, "gethostbyname2_r");

The void ** vs concrete pointer example is __nss_getent.

For __nss_getent, it wouldn't be too hard to split the buffer management
from the call, and move the call to the caller of __nss_getent, where
the correct type is known.

getaddrinfo may be harder and involve splitting the code around the caller.

Florian