[libcxx-commits] [libcxx] [libcxx] Use alias for detecting overriden function (PR #114961)

[Petr Hosek via libcxx-commits]

================
@@ -42,93 +42,74 @@
 // -------------------
 //
 // Let's say we want to check whether a weak function `f` has been overridden by the user.
-// The general mechanism works by placing `f`'s definition (in the libc++ built library)
-// inside a special section, which we do using the `__section__` attribute via the
-// _LIBCPP_MAKE_OVERRIDABLE_FUNCTION_DETECTABLE macro.
+// The general mechanism works by defining a symbol `f_impl__` and a weak alias `f` via the
+// _LIBCPP_OVERRIDABLE_FUNCTION macro.
 //
 // Then, when comes the time to check whether the function has been overridden, we take
-// the address of the function and we check whether it falls inside the special function
-// we created. This can be done by finding pointers to the start and the end of the section
-// (which is done differently for ELF and Mach-O), and then checking whether `f` falls
-// within those bounds. If it falls within those bounds, then `f` is still inside the
-// special section and so it is the version we defined in the libc++ built library, i.e.
-// it was not overridden. Otherwise, it was overridden by the user because it falls
-// outside of the section.
+// the address of the function `f` and we check whether it is different from `f_impl__`.
+// If so it means the function was overriden by the user.
 //
 // Important note
 // --------------
 //
-// This mechanism should never be used outside of the libc++ built library. In particular,
-// attempting to use this within the libc++ headers will not work at all because we don't
-// want to be defining special sections inside user's executables which use our headers.
+// This mechanism should never be used outside of the libc++ built library.
----------------
petrhosek wrote:

Done.

https://github.com/llvm/llvm-project/pull/114961