[PATCH RFC v2 0/8] termios: support arbitrary baud rates on Linux, minor cleanups, proposed alternative interface

[Joseph Myers]

On Fri, 25 Apr 2025, H. Peter Anvin wrote:

> 2. When to use __foo() functions. In my patches I have assumed that
>    calls internal to glibc.so should be using __foo() not foo(), but I
>    got a very muddy reply as to "when things cross namespace
>    boundaries", pointing me to a document which brought absolutely no
>    clarity to the issue.

There are two separate but sometimes linked issues:

* Namespace issues (mainly for static linking): if e.g. an ISO C function 
calls a POSIX one (directly or indirectly), the call needs to use a name 
__* in the implementation namespace.  The linknamespace tests should 
detect violations of this for the standards that they cover.  This issue 
does not apply if the function being called is in all the standards that 
contain the caller.

* PLT avoidance: internal calls within libc.so should not be interposable, 
meaning they should use a function name not exported from the library.  
This can be achieved via libc_hidden_proto / libc_hidden_def which result 
in a hidden alias being used for the calls; if an internal name __* that's 
not exported is used, those aren't needed (although they are often used 
for such names as well) - but in that case, if not using libc_hidden_*, 
the internal name should preferably be declared with attribute_hidden 
(since sometimes it's beneficial for code generation for it to be visible 
at compile time, not just link time, that the call is to a non-exported 
name).

-- 
Joseph S. Myers
josmyers@redhat.com