[ELF] Add REVERSE input section description keyword

The `REVERSE` keyword is described here:

https://sourceware.org/bugzilla/show_bug.cgi?id=27565

It complements `SORT` by allowing the order of input sections to be reversed.

This is particularly useful for order-dependent sections such as .init_array,
where `REVERSE` can be used to either detect static initialization order fiasco
issues or as a mechanism to maintain .ctors element order while transitioning to
the modern .init_array. Such a transition is described here:

https://discourse.llvm.org/t/is-it-possible-to-manually-specify-init-array-order/68649

Differential Revision: https://reviews.llvm.org/D145381

1 files changed, 2 insertions, 0 deletions

diff --git a/lld/ELF/LinkerScript.cpp b/lld/ELF/LinkerScript.cpp
index 668a79b5edd7..9207751cb7d2 100644
--- a/lld/ELF/LinkerScript.cpp
+++ b/lld/ELF/LinkerScript.cpp
@@ -457,6 +457,8 @@ static void sortSections(MutableArrayRef<InputSectionBase *> vec,
     return llvm::stable_sort(vec, nameComparator);
   case SortSectionPolicy::Priority:
     return llvm::stable_sort(vec, priorityComparator);
+  case SortSectionPolicy::Reverse:
+    return std::reverse(vec.begin(), vec.end());
   }
 }