[llvm-objcopy] Skip --localize-symbol for undefined symbols

Summary:
Include the symbol being defined in the list of requirements for using --localize-symbol.

This is used, for example, when someone is depending on two different projects that have the same (or close enough) method defined in each library, and using "-L sym" for a conflicting symbol in one of the libraries so that the definition from the other one is used. However, the library may have internal references to the symbol, which cause program crashes when those are used, i.e.:

```
$ cat foo.c
int foo() { return 5; }
$ cat bar.c
int foo();
int bar() { return 2 * foo(); }
$ cat foo2.c
int foo() { /* Safer implementation */ return 42; }
$ cat main.c
int bar();
int main() {
  __builtin_printf("bar = %d\n", bar());
  return 0;
}
$ ar rcs libfoo.a foo.o bar.o
$ ar rcs libfoo2.a foo2.o
# Picks the wrong foo() impl
$ clang main.o -lfoo -lfoo2 -L. -o main
# Picks the right foo() impl
$ objcopy -L foo libfoo.a && clang main.o -lfoo -lfoo2 -L. -o main
# Links somehow, but crashes at runtime
$ llvm-objcopy -L foo libfoo.a && clang main.o -lfoo -lfoo2 -L. -o main
```

Reviewers: jhenderson, alexshap, jakehehrlich, espindola

Subscribers: emaste, arichardson

Differential Revision: https://reviews.llvm.org/D57417

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@352767 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/test/tools/llvm-objcopy/ELF/localize.test b/test/tools/llvm-objcopy/ELF/localize.test
index a04c51d8fc105d94491b55a117753110f76f8121..50cdce78da16380a3f16a85dc5c5d3badfee7694 100644 (file)
--- a/test/tools/llvm-objcopy/ELF/localize.test
+++ b/test/tools/llvm-objcopy/ELF/localize.test
@@ -1,6 +1,7 @@
 # RUN: yaml2obj %s > %t
 # RUN: llvm-objcopy \
 # RUN:     --localize-symbol Global \
+# RUN:     -L GlobalUndef \
 # RUN:     -L Local \
 # RUN:     -L Weak \
 # RUN:     -L GlobalCommon \
@@ -45,6 +46,8 @@ Symbols:
       Size:     8
       Section:  .text
       Value:    0x1010
+    - Name:     GlobalUndef
+      Type:     STT_FUNC
     - Name:     GlobalCommon
       Type:     STT_OBJECT
       Index:    SHN_COMMON
@@ -89,6 +92,15 @@ Symbols:
 #CHECK-NEXT:    Section: .text
 #CHECK-NEXT:  }
 #CHECK-NEXT:  Symbol {
+#CHECK-NEXT:    Name: GlobalUndef
+#CHECK-NEXT:    Value:
+#CHECK-NEXT:    Size:
+#CHECK-NEXT:    Binding: Global
+#CHECK-NEXT:    Type: Function
+#CHECK-NEXT:    Other:
+#CHECK-NEXT:    Section: Undefined
+#CHECK-NEXT:  }
+#CHECK-NEXT:  Symbol {
 #CHECK-NEXT:    Name: GlobalCommon
 #CHECK-NEXT:    Value: 0x2006
 #CHECK-NEXT:    Size: 2

diff --git a/tools/llvm-objcopy/ELF/ELFObjcopy.cpp b/tools/llvm-objcopy/ELF/ELFObjcopy.cpp
index e77361e285a0e4e078f3bb1b71eca862b7061737..2dd2fe9c9a9b03d95be6e8d58ac1bee6c9f59935 100644 (file)
--- a/tools/llvm-objcopy/ELF/ELFObjcopy.cpp
+++ b/tools/llvm-objcopy/ELF/ELFObjcopy.cpp
@@ -287,7 +287,9 @@ static Error handleArgs(const CopyConfig &Config, Object &Obj,
   // them.
   if (Obj.SymbolTable) {
     Obj.SymbolTable->updateSymbols([&](Symbol &Sym) {
-      if (!Sym.isCommon() &&
+      // Common and undefined symbols don't make sense as local symbols, and can
+      // even cause crashes if we localize those, so skip them.
+      if (!Sym.isCommon() && Sym.getShndx() != SHN_UNDEF &&
           ((Config.LocalizeHidden &&
             (Sym.Visibility == STV_HIDDEN || Sym.Visibility == STV_INTERNAL)) ||
            is_contained(Config.SymbolsToLocalize, Sym.Name)))