From 5d3feefa0df9c054f6d683ca13316a822b596f87 Mon Sep 17 00:00:00 2001
From: Jez Ng <jezng@fb.com>
Date: Wed, 29 Apr 2020 05:30:47 -0700
Subject: [PATCH] [lld-macho] Dylib symbols should always replace undefined
 symbols

Summary:
Otherwise we get undefined symbol errors depending on the order of
arguments on the command line.

Depends on D78270.

Reviewers: ruiu, pcc, MaskRay, smeenai, alexshap, gkm, Ktwu, christylee

Subscribers: llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D79114
---
 lld/MachO/SymbolTable.cpp   |  2 +-
 lld/test/MachO/resolution.s | 44 +++++++++++++++++++++++++++++++++++++
 2 files changed, 45 insertions(+), 1 deletion(-)
 create mode 100644 lld/test/MachO/resolution.s

diff --git a/lld/MachO/SymbolTable.cpp b/lld/MachO/SymbolTable.cpp
index 41446d6df4db..6e1d9771c965 100644
--- a/lld/MachO/SymbolTable.cpp
+++ b/lld/MachO/SymbolTable.cpp
@@ -64,7 +64,7 @@ Symbol *SymbolTable::addDylib(StringRef name, DylibFile *file) {
   bool wasInserted;
   std::tie(s, wasInserted) = insert(name);
 
-  if (wasInserted)
+  if (wasInserted || isa<Undefined>(s))
     replaceSymbol<DylibSymbol>(s, file, name);
   return s;
 }
diff --git a/lld/test/MachO/resolution.s b/lld/test/MachO/resolution.s
new file mode 100644
index 000000000000..a13bb529cf7f
--- /dev/null
+++ b/lld/test/MachO/resolution.s
@@ -0,0 +1,44 @@
+# REQUIRES: x86
+# RUN: mkdir -p %t
+# RUN: echo '.globl _foo, _bar, _baz; _foo: _bar: _baz:' | \
+# RUN:   llvm-mc -filetype=obj -triple=x86_64-apple-darwin -o %t/libresolution.o
+# RUN: lld -flavor darwinnew -dylib -install_name \
+# RUN:   @executable_path/libresolution.dylib %t/libresolution.o -o %t/libresolution.dylib
+# RUN: lld -flavor darwinnew -dylib -install_name \
+# RUN:   @executable_path/libresolution2.dylib %t/libresolution.o -o %t/libresolution2.dylib
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t/resolution.o
+
+## Check that we select the symbol defined in the first dylib passed on the
+## command line.
+# RUN: lld -flavor darwinnew -o %t/dylib-first -Z -L%t -lresolution -lresolution2 %t/resolution.o
+# RUN: llvm-objdump --macho --bind %t/dylib-first | FileCheck %s --check-prefix=DYLIB-FIRST
+# DYLIB-FIRST:     libresolution _foo
+
+# RUN: lld -flavor darwinnew -o %t/dylib2-first -Z -L%t -lresolution2 -lresolution %t/resolution.o
+# RUN: llvm-objdump --macho --bind %t/dylib2-first | FileCheck %s --check-prefix=DYLIB2-FIRST
+# DYLIB2-FIRST: libresolution2 _foo
+
+## Also check that defined symbols take precedence over dylib symbols.
+# DYLIB-FIRST-NOT: libresolution _bar
+# DYLIB-FIRST-NOT: libresolution _baz
+
+## Check that we pick the dylib symbol over the undefined symbol in the object
+## file, even if the object file appears first on the command line.
+# RUN: lld -flavor darwinnew -o %t/obj-first -Z -L%t %t/resolution.o -lresolution
+# RUN: llvm-objdump --macho --bind %t/obj-first | FileCheck %s --check-prefix=OBJ-FIRST
+# OBJ-FIRST: libresolution _foo
+## But defined symbols should still take precedence.
+# OBJ-FIRST-NOT: libresolution _bar
+# OBJ-FIRST-NOT: libresolution _baz
+
+.globl _main, _bar
+# Global defined symbol
+_bar:
+# Local defined symbol
+_baz:
+
+_main:
+  movq _foo@GOTPCREL(%rip), %rsi
+  movq _bar@GOTPCREL(%rip), %rsi
+  movq _baz@GOTPCREL(%rip), %rsi
+  ret