[cxx-abi-dev] On __func__

[Richard Smith]

Hi!

Per C++ [dcl.fct.def.general]p8, __func__ acts as if it were defined as a
static local variable defined within the surrounding function. This has two
impacts on the ABI which we don't seem to capture today, and for which
implementations vary. Consider:

inline const char *f() { return __func__; }

To my reading, the standard requires f() to return the same pointer in
every translation unit. But... what is the mangled name of that string
literal, and what does it contain? (We must produce the same contents in
every TU in order to give it the same type.)

Implementations vary only slightly on the first question. GCC mangles it
as _ZZ1fvE8__func__ but makes the symbol internal. EDG and Clang make it
internal with no particular symbol. None of these approaches is conforming.
We could perhaps call this a standard defect: perhaps the address of the
object named by __func__ should be permitted to differ on each evaluation.

Implementations vary much more significantly on the second question, giving
different values (and thus different types) for __func__ in the same inline
function. Is there anything we can do to make this work? I don't see any
good options here, but I wanted to check with this group before suggesting
the standard be changed (for instance, by making __func__ a prvalue of type
'const char*' rather than an lvalue of type 'const char[N]').

Thoughts?
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