[Bug build/27596] bits/libc-header-start.h is C++ header-unit unfriendly

["joseph at codesourcery dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=27596

--- Comment #1 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
The handling of __GLIBC_INTERNAL_STARTING_HEADER_IMPLEMENTATION is a check 
to discourage external users from using something that's not a public API, 
rather than something strictly required.

bits/libc-header-start.h will produce different macro definitions when 
included with different feature test macros defined.  It's valid for that 
to occur within the compilation of a single translation unit - for one of 
the ISO C feature test macros to be defined after some headers have been 
included and before others are included.  The peculiarities of how those 
ISO C feature test macros are defined are why this header is separate from 
features.h and can't have multiple-include protection.

If the rules that the definitions from a header depend on what feature 
test macros were defined when *that header* is first included (as opposed 
to it being required to define feature test macros before including any 
standard header, as in POSIX) are problematic for C++, that seems like a 
good thing to raise on the C/C++ liaison mailing list.  Or is the issue 
only with the particular approach to implementing that requirement, rather 
than with the requirement itself?

-- 
You are receiving this mail because:
You are on the CC list for the bug.