[llvm-ar] Fix for handling thin archive with SYM64 and a test case for it

[Ramesh]

Summary

WHen thin archives are created which have symbol table of type SYM64 then all the tools will not work since they cannot read the files properly.
One can reproduce the problem as follows:

1. Take a hello world program and create an archive out of it. The SYM64_THRESHOLD=0 will force the generation of SYM64 symbol table. clang -c hello.cpp SYM64_THRESHOLD=0 llvm-ar crsT mylib.a hello.o
2. Now try to use any of the tools on this mylib.a and it will fail. llvm-nm -M mylib.a

THis fix will eliminate these failures. A regression test is created in llvm/test/Object/archive-symtab.test

[MaskRay]

LG

llvm/test/Object/archive-symtab.test

55

-M => --print-armap

-M was inappropriately added when -s was taken by Darwin nm. -M will be removed and should not be used.

68

drop unrelated change

[Ramesh]

llvm/test/Object/archive-symtab.test

55

There are a number of other tests which are using this option still - what needs to be done about them?

68

Will fix it.

[Ramesh]

Address reviwer comments

[MaskRay]

Thanks! I migrated these -M to --print-armap

llvm/lib/Object/Archive.cpp

Expected<uint64_t> Archive::Child::getRawSize() const {
   return Header.getSize();
 }
 
 Expected<bool> Archive::Child::isThinMember() const {
   Expected<StringRef> NameOrErr = Header.getRawName();
   if (!NameOrErr)
     return NameOrErr.takeError();
   StringRef Name = NameOrErr.get();
-  return Parent->IsThin && Name != "/" && Name != "//";
+  return Parent->IsThin && Name != "/" && Name != "//" && Name != "/SYM64/";
 }
 
 Expected<std::string> Archive::Child::getFullName() const {
   Expected<bool> isThin = isThinMember();
   if (!isThin)
     return isThin.takeError();
   assert(isThin.get());
   Expected<StringRef> NameOrErr = getName();

llvm/test/Object/archive-symtab.test

- Name:    main
     Binding: STB_GLOBAL
     Value:   0x0000000000000016
 
 # RUN: rm -f %t.a
 # RUN: llvm-ar rcsU %t.a %t.elf-x86-64 %t2.elf-x86-64
 # RUN: llvm-nm --print-armap %t.a | FileCheck %s
 
 # RUN: rm -f %t.a
+# RUN: env SYM64_THRESHOLD=0 llvm-ar crTs %t.a %t.elf-x86-64 %t2.elf-x86-64
+# RUN: llvm-nm --print-armap  %t.a | FileCheck %s
+# RUN: grep '/SYM64/' %t.a
+ 
+# RUN: rm -f %t.a
 # RUN: env SYM64_THRESHOLD=836 llvm-ar rcsU %t.a %t.elf-x86-64 %t2.elf-x86-64
 # RUN: llvm-nm --print-armap %t.a | FileCheck %s
 # RUN: grep '/SYM64/' %t.a
 
 # RUN: rm -f %t.a
 # RUN: env SYM64_THRESHOLD=837 llvm-ar rcsU %t.a %t.elf-x86-64 %t2.elf-x86-64
 # RUN: llvm-nm --print-armap %t.a | FileCheck %s
 # RUN: not grep '/SYM64/' %t.a
 
 # CHECK: Archive map
 # CHECK-NEXT: main in {{.*}}.elf-x86-64
 # CHECK-NEXT: foo in {{.*}}2.elf-x86-64
 # CHECK-NEXT: main in {{.*}}2.elf-x86-64
 # CHECK-NOT: bar
 
 
 # RUN: rm -f %t.a
 # RUN: llvm-ar --format=gnu rcT %t.a %t.elf-x86-64 %t2.elf-x86-64