[lld] [lld-macho] Add support for category names in ConcatInputSection's (PR #90850)

[via llvm-commits]

https://github.com/alx32 updated https://github.com/llvm/llvm-project/pull/90850

>From c098eb08a9306b795c273d88c18b8c42f4949434 Mon Sep 17 00:00:00 2001
From: Alex Borcan <alexborcan at fb.com>
Date: Thu, 2 May 2024 05:22:23 -0700
Subject: [PATCH 1/3] [lld-macho] Add support for category names in
 ConcatInputSection's

---
 lld/MachO/ObjC.cpp                              | 17 ++++++++++++++---
 ...objc-category-merging-extern-class-minimal.s |  2 +-
 2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/lld/MachO/ObjC.cpp b/lld/MachO/ObjC.cpp
index 95fe0c9374f150..68a8645532dff6 100644
--- a/lld/MachO/ObjC.cpp
+++ b/lld/MachO/ObjC.cpp
@@ -186,13 +186,24 @@ ObjcCategoryChecker::ObjcCategoryChecker()
       roClassLayout(target->wordSize), listHeaderLayout(target->wordSize),
       methodLayout(target->wordSize) {}
 
-// \p r must point to an offset within a cstring section.
+// \p r must point to an offset within a CStringInputSection or a
+// ConcatInputSection
 static StringRef getReferentString(const Reloc &r) {
   if (auto *isec = r.referent.dyn_cast<InputSection *>())
     return cast<CStringInputSection>(isec)->getStringRefAtOffset(r.addend);
   auto *sym = cast<Defined>(r.referent.get<Symbol *>());
-  return cast<CStringInputSection>(sym->isec())
-      ->getStringRefAtOffset(sym->value + r.addend);
+  if (isa<CStringInputSection>(sym->isec()))
+    return cast<CStringInputSection>(sym->isec())
+        ->getStringRefAtOffset(sym->value + r.addend);
+
+  if (isa<ConcatInputSection>(sym->isec())) {
+    auto &data = sym->isec()->data;
+    const char *pDataStart = reinterpret_cast<const char *>(data.data());
+    uint32_t len = strnlen(pDataStart + sym->value, data.size() - sym->value);
+    return StringRef(pDataStart + sym->value, len);
+  }
+
+  llvm_unreachable("unknown reference section in getReferentString");
 }
 
 void ObjcCategoryChecker::parseMethods(const ConcatInputSection *methodsIsec,
diff --git a/lld/test/MachO/objc-category-merging-extern-class-minimal.s b/lld/test/MachO/objc-category-merging-extern-class-minimal.s
index ede7ef5d9c32d4..3e220ef372ca0d 100644
--- a/lld/test/MachO/objc-category-merging-extern-class-minimal.s
+++ b/lld/test/MachO/objc-category-merging-extern-class-minimal.s
@@ -118,7 +118,7 @@ __OBJC_$_CATEGORY_MyBaseClass_$_Category01:
 	.quad	0
 	.long	64                              ; 0x40
 	.space	4
-	.section	__TEXT,__objc_classname,cstring_literals
+	.section	__DATA,__objc_const
 l_OBJC_CLASS_NAME_.1:                   ; @OBJC_CLASS_NAME_.1
 	.asciz	"Category02"
 	.section	__TEXT,__objc_methname,cstring_literals

>From ff064bb7c10efff165937e94229ce4a10bb4039e Mon Sep 17 00:00:00 2001
From: alx32 <103613512+alx32 at users.noreply.github.com>
Date: Thu, 2 May 2024 13:56:33 -0700
Subject: [PATCH 2/3] Apply suggestions from code review

Address Feedback nr.1

Co-authored-by: Ellis Hoag <ellis.sparky.hoag at gmail.com>
---
 lld/MachO/ObjC.cpp | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/lld/MachO/ObjC.cpp b/lld/MachO/ObjC.cpp
index 68a8645532dff6..973b4fec95cc4a 100644
--- a/lld/MachO/ObjC.cpp
+++ b/lld/MachO/ObjC.cpp
@@ -192,9 +192,8 @@ static StringRef getReferentString(const Reloc &r) {
   if (auto *isec = r.referent.dyn_cast<InputSection *>())
     return cast<CStringInputSection>(isec)->getStringRefAtOffset(r.addend);
   auto *sym = cast<Defined>(r.referent.get<Symbol *>());
-  if (isa<CStringInputSection>(sym->isec()))
-    return cast<CStringInputSection>(sym->isec())
-        ->getStringRefAtOffset(sym->value + r.addend);
+  if (auto *s = dyn_cast_or_null<CStringInputSection>(sym->isec()))
+    return s->getStringRefAtOffset(sym->value + r.addend);
 
   if (isa<ConcatInputSection>(sym->isec())) {
     auto &data = sym->isec()->data;

>From 81f8dcc25ecc503f20089127df5f4b4dc7292cf9 Mon Sep 17 00:00:00 2001
From: Alex Borcan <alexborcan at fb.com>
Date: Thu, 2 May 2024 15:54:57 -0700
Subject: [PATCH 3/3] Address Feedback nr.2

---
 lld/MachO/ObjC.cpp | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/lld/MachO/ObjC.cpp b/lld/MachO/ObjC.cpp
index 973b4fec95cc4a..bb8b131514e7ed 100644
--- a/lld/MachO/ObjC.cpp
+++ b/lld/MachO/ObjC.cpp
@@ -196,10 +196,10 @@ static StringRef getReferentString(const Reloc &r) {
     return s->getStringRefAtOffset(sym->value + r.addend);
 
   if (isa<ConcatInputSection>(sym->isec())) {
-    auto &data = sym->isec()->data;
-    const char *pDataStart = reinterpret_cast<const char *>(data.data());
-    uint32_t len = strnlen(pDataStart + sym->value, data.size() - sym->value);
-    return StringRef(pDataStart + sym->value, len);
+    auto paddedData = sym->isec()->data.slice(sym->value);
+    uint32_t len = strnlen((const char *)paddedData.data(), paddedData.size());
+    auto strData = paddedData.slice(0, len);
+    return StringRef((const char *)strData.data(), strData.size());
   }
 
   llvm_unreachable("unknown reference section in getReferentString");