[ELF] - Allow discarding .hash and .gnu.hash from linker script.

Currently, LLD segfaults when linker script attempts to discard
one of the hash sections. This patch fixes that.

Differential revision: https://reviews.llvm.org/D44012

llvm-svn: 326891

lld/ELF/LinkerScript.cpp

@@ -380,6 +380,14 @@ void LinkerScript::discard(ArrayRef<InputSection *> V) {
         S == InX::DynStrTab)
       error("discarding " + S->Name + " section is not allowed");
 
+    // You can discard .hash and .gnu.hash sections by linker scripts. Since
+    // they are synthesized sections, we need to handle them differently than
+    // other regular sections.
+    if (S == InX::GnuHashTab)
+      InX::GnuHashTab = nullptr;
+    if (S == InX::HashTab)
+      InX::HashTab = nullptr;
+
     S->Assigned = false;
     S->Live = false;
     discard(S->DependentSections);

lld/test/ELF/linkerscript/discard-gnu-hash.s

@@ -0,0 +1,23 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
+
+# RUN: ld.lld --hash-style both -shared -o %t1 %t
+# RUN: llvm-objdump -section-headers %t1 | FileCheck %s
+# CHECK: .gnu.hash
+# CHECK: .hash
+
+# RUN: echo "SECTIONS { /DISCARD/ : { *(.hash) } }" > %t.script
+# RUN: ld.lld --hash-style both -shared -o %t1 --script %t.script %t
+# RUN: llvm-objdump -section-headers %t1 \
+# RUN:   | FileCheck %s --check-prefix=HASH
+# HASH-NOT: .hash
+# HASH:     .gnu.hash
+# HASH-NOT: .hash
+
+# RUN: echo "SECTIONS { /DISCARD/ : { *(.gnu.hash) } }" > %t.script
+# RUN: ld.lld --hash-style both -shared -o %t1 --script %t.script %t
+# RUN: llvm-objdump -section-headers %t1 \
+# RUN:   | FileCheck %s --check-prefix=GNUHASH
+# GNUHASH-NOT: .gnu.hash
+# GNUHASH:     .hash
+# GNUHASH-NOT: .gnu.hash