Move the hashed __retguard_* symbols into individual sections and mark

them as COMDATs so that the linker can individually discard them, instead
of just ignoring duplicate symbols but keep the (duplicate) space.

On amd64, this reduces the size of the kernel OPENBSD_RANDOM segment by 82%
and the libc OPENBSD_RANDOM segment by 15%.  A port that tb@ is working
on experienced a 97.3% reduction...which let it actually run.

ok mortimer@ deraadt@

1 files changed, 5 insertions, 3 deletions

diff --git a/gnu/llvm/lib/CodeGen/ReturnProtectorPass.cpp b/gnu/llvm/lib/CodeGen/ReturnProtectorPass.cpp
index a8b588989a5..ba92469493a 100644
--- a/gnu/llvm/lib/CodeGen/ReturnProtectorPass.cpp
+++ b/gnu/llvm/lib/CodeGen/ReturnProtectorPass.cpp
@@ -33,14 +33,16 @@ namespace {
         // Create a symbol for the cookie
         Module *M = F.getParent();
         std::hash<std::string> hasher;
-        std::string cookiename = "__retguard_" + std::to_string(hasher((M->getName() + F.getName()).str()) % 4000);
+        std::string hash = std::to_string(hasher((M->getName() + F.getName()).str()) % 4000);
+        std::string cookiename = "__retguard_" + hash;
         Type *cookietype = Type::getInt8PtrTy(M->getContext());
         GlobalVariable *cookie = dyn_cast_or_null<GlobalVariable>(
             M->getOrInsertGlobal(cookiename, cookietype));
         cookie->setInitializer(Constant::getNullValue(cookietype));
-        cookie->setLinkage(GlobalVariable::WeakAnyLinkage);
+        cookie->setLinkage(GlobalVariable::LinkOnceAnyLinkage);
         cookie->setVisibility(GlobalValue::HiddenVisibility);
-        cookie->setSection(".openbsd.randomdata.retguard");
+        cookie->setComdat(M->getOrInsertComdat(cookiename));
+        cookie->setSection(".openbsd.randomdata.retguard." + hash);
         cookie->setExternallyInitialized(true);
         F.addFnAttr("ret-protector-cookie", cookiename);
         NumSymbols++;