Make operator new/delete symbols have default visibility

third_party/libc++/BUILD.gn

Index: third_party/libc++/BUILD.gn
diff --git a/third_party/libc++/BUILD.gn b/third_party/libc++/BUILD.gn
index ff51ab9260f771fcdafc6fa7f937bbe0dff607aa..2ffd28523a0b49637dce155d4401849698651275 100644
--- a/third_party/libc++/BUILD.gn
+++ b/third_party/libc++/BUILD.gn
@@ -18,6 +18,13 @@ config("config") {
     defines += [
       "_LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS",
       "_LIBCXXABI_DISABLE_VISIBILITY_ANNOTATIONS",
+
+      # This resets the visibility to default only for the various
+      # flavors of operator new and operator delete.  These symbols
+      # are weak and get overriden by Chromium-provided ones, but if
+      # these symbols had hidden visibility, this would make the
+      # Chromium symbols hidden too.
+      "_LIBCPP_OVERRIDABLE_FUNC_VIS=__attribute__((__visibility__(\"default\")))",

[Nico, 2017/06/19 19:22:41]

Can you add a comment here along the lines of "
elf visibility rules require that linkers use the least visible form when
merging, and if this is hidden, then when we merge it with tcmalloc's operator
new, hidden visibility would win. Hoever, tcmalloc needs a visible operator new
to also override operator new references from system libraries.
TODO(lld): Ask lld for a --force-public-visibility flag or similar to that
overrides the default elf merging rules, and make tcmalloc's gn config pass that
to all its dependencies, then remove this override here."

[Tom Anderson, 2017/06/19 19:27:40]

Done.

     ]
   }
   cflags = [