From c5c05ffa4562223cae7db537ca7772afaeccd009 Mon Sep 17 00:00:00 2001
From: Jez Ng <jezng@fb.com>
Date: Sun, 13 Jun 2021 19:43:36 -0400
Subject: [PATCH] [lld-macho][nfc] Represent the image loader cache with a
 ConcatInputSection

We don't need to define any special behavior for this section,
so creating a subclass for it is redundant.

Reviewed By: #lld-macho, thakis

Differential Revision: https://reviews.llvm.org/D104199
---
 lld/MachO/SyntheticSections.cpp |  9 ---------
 lld/MachO/SyntheticSections.h   | 12 +-----------
 lld/MachO/Writer.cpp            | 12 +++++++++++-
 3 files changed, 12 insertions(+), 21 deletions(-)

diff --git a/lld/MachO/SyntheticSections.cpp b/lld/MachO/SyntheticSections.cpp
index f402ff6..5f2d446 100644
--- a/lld/MachO/SyntheticSections.cpp
+++ b/lld/MachO/SyntheticSections.cpp
@@ -477,15 +477,6 @@ void StubHelperSection::setup() {
                     /*noDeadStrip=*/false);
 }
 
-ImageLoaderCacheSection::ImageLoaderCacheSection()
-    : ConcatInputSection(segment_names::data, section_names::data) {
-  uint8_t *arr = bAlloc.Allocate<uint8_t>(target->wordSize);
-  memset(arr, 0, target->wordSize);
-  data = {arr, target->wordSize};
-  align = target->wordSize;
-  live = true;
-}
-
 LazyPointerSection::LazyPointerSection()
     : SyntheticSection(segment_names::data, section_names::lazySymbolPtr) {
   align = target->wordSize;
diff --git a/lld/MachO/SyntheticSections.h b/lld/MachO/SyntheticSections.h
index bde3b3b..4e3ea69 100644
--- a/lld/MachO/SyntheticSections.h
+++ b/lld/MachO/SyntheticSections.h
@@ -326,16 +326,6 @@ public:
   Defined *dyldPrivate = nullptr;
 };
 
-// This section contains space for just a single word, and will be used by dyld
-// to cache an address to the image loader it uses. Note that unlike the other
-// synthetic sections, which are OutputSections, the ImageLoaderCacheSection is
-// an InputSection that gets merged into the __data OutputSection.
-class ImageLoaderCacheSection : public ConcatInputSection {
-public:
-  ImageLoaderCacheSection();
-  uint64_t getSize() const override { return target->wordSize; }
-};
-
 // Note that this section may also be targeted by non-lazy bindings. In
 // particular, this happens when branch relocations target weak symbols.
 class LazyPointerSection : public SyntheticSection {
@@ -600,8 +590,8 @@ struct InStruct {
   LazyPointerSection *lazyPointers = nullptr;
   StubsSection *stubs = nullptr;
   StubHelperSection *stubHelper = nullptr;
-  ImageLoaderCacheSection *imageLoaderCache = nullptr;
   UnwindInfoSection *unwindInfo = nullptr;
+  ConcatInputSection *imageLoaderCache = nullptr;
 };
 
 extern InStruct in;
diff --git a/lld/MachO/Writer.cpp b/lld/MachO/Writer.cpp
index 6626b52..40f27fa 100644
--- a/lld/MachO/Writer.cpp
+++ b/lld/MachO/Writer.cpp
@@ -1070,8 +1070,18 @@ void macho::createSyntheticSections() {
   in.lazyPointers = make<LazyPointerSection>();
   in.stubs = make<StubsSection>();
   in.stubHelper = make<StubHelperSection>();
-  in.imageLoaderCache = make<ImageLoaderCacheSection>();
   in.unwindInfo = makeUnwindInfoSection();
+
+  // This section contains space for just a single word, and will be used by
+  // dyld to cache an address to the image loader it uses.
+  ArrayRef<uint8_t> data{bAlloc.Allocate<uint8_t>(target->wordSize),
+                         target->wordSize};
+  in.imageLoaderCache = make<ConcatInputSection>(
+      segment_names::data, section_names::data, /*file=*/nullptr, data,
+      /*align=*/target->wordSize, /*flags=*/S_REGULAR);
+  // References from dyld are not visible to us, so ensure this section is
+  // always treated as live.
+  in.imageLoaderCache->live = true;
 }
 
 OutputSection *macho::firstTLVDataSection = nullptr;
-- 
2.7.4