[PATCH] D157300: [lld-macho]Rework error-checking in peeking at first-member in archive to avoid segfault.

[Vy Nguyen via Phabricator via llvm-commits]

oontvoo updated this revision to Diff 548594.
oontvoo added a comment.

rebase


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D157300/new/

https://reviews.llvm.org/D157300

Files:
  lld/MachO/InputFiles.cpp
  lld/test/MachO/force-load.s


Index: lld/test/MachO/force-load.s
===================================================================
--- lld/test/MachO/force-load.s
+++ lld/test/MachO/force-load.s
@@ -42,6 +42,12 @@
 # TWICE-DAG: __TEXT,archive _bar
 # TWICE-DAG: __TEXT,archive _baz
 
+## Loading an empty-archive should not crash.
+# RUN: llvm-ar --format=darwin rcs %t/libEmpty.a
+# RUN: %lld -lSystem %t/test.o -force_load %t/libEmpty.a -o %t/loadEmpty.out
+# RUN: llvm-objdump --macho --syms %t/loadEmpty.out | FileCheck %s --check-prefix=EMPTY
+# EMPTY: F __TEXT,__text _main
+
 #--- archive-foo.s
 .section __TEXT,archive
 .globl _foo, _bar
Index: lld/MachO/InputFiles.cpp
===================================================================
--- lld/MachO/InputFiles.cpp
+++ lld/MachO/InputFiles.cpp
@@ -2106,28 +2106,34 @@
       forceHidden(forceHidden) {}
 
 void ArchiveFile::addLazySymbols() {
-  Error err = Error::success();
-  Expected<MemoryBufferRef> mbOrErr =
-      this->file->child_begin(err)->getMemoryBufferRef();
+  // Avoid calling getMemoryBufferRef() on zero-symbol archive
+  // since that crashes.
+  if (file->isEmpty() || file->getNumberOfSymbols() == 0)
+    return;
 
+  Error err = Error::success();
+  auto child = file->child_begin(err);
   // Ignore the I/O error here - will be reported later.
-  if (!mbOrErr) {
-    llvm::consumeError(mbOrErr.takeError());
-  } else if (!err) {
-    if (identify_magic(mbOrErr->getBuffer()) == file_magic::macho_object) {
-      if (target->wordSize == 8)
-        compatArch = compatWithTargetArch(
-            this, reinterpret_cast<const LP64::mach_header *>(
-                      mbOrErr->getBufferStart()));
-      else
-        compatArch = compatWithTargetArch(
-            this, reinterpret_cast<const ILP32::mach_header *>(
-                      mbOrErr->getBufferStart()));
-
-      if (!compatArch)
-        return;
+  if (!err) {
+    Expected<MemoryBufferRef> mbOrErr = child->getMemoryBufferRef();
+    if (!mbOrErr) {
+      llvm::consumeError(mbOrErr.takeError());
+    } else {
+      if (identify_magic(mbOrErr->getBuffer()) == file_magic::macho_object) {
+        if (target->wordSize == 8)
+          compatArch = compatWithTargetArch(
+              this, reinterpret_cast<const LP64::mach_header *>(
+                        mbOrErr->getBufferStart()));
+        else
+          compatArch = compatWithTargetArch(
+              this, reinterpret_cast<const ILP32::mach_header *>(
+                        mbOrErr->getBufferStart()));
+        if (!compatArch)
+          return;
+      }
     }
   }
+
   for (const object::Archive::Symbol &sym : file->symbols())
     symtab->addLazyArchive(sym.getName(), this, sym);
 }


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