Re: glibc strerrorname_np

["Zack Weinberg" <zack@owlfolio.org>]

On Sat, Nov 6, 2021, at 8:51 AM, Adhemerval Zanella via Libc-alpha wrote:
> On 05/11/2021 19:23, Jonny Grant wrote:
>> On 05/11/2021 13:01, Adhemerval Zanella wrote:
>>> On 05/11/2021 08:51, Jonny Grant wrote:
>>>> Thank you for your reply. Personally I understood an ABI break would be
>>>> the return type, the name, or the parameters. But the proposed change is
>>>> not so. Changing to return a string, should be fine.
>>>
>>> It is still an ABI break, code that checks NULL for invalid input will
>>> stop to work.
...
> As I said before it is an ABI break, since users that check for invalid 
> errno against NULL will start to fail.  For such change we *do need* all 
> the trouble of adding a compat symbol with current semantic.

A compat symbol doesn't do any good here, though.  As soon as the program is recompiled it will start getting the new semantics, and since that doesn't cause a compile-time error, the break will go unnoticed -- particularly in this case, since this is likely to affect only error-handling paths that test suites tend not to exercise.

If we want to preserve backward compatibility we need a whole new function name.

zw