[RuntimeDyld][ELF] Fixed relocations referencing undefined TLS symbols

[MoritzS]

Summary

The classification of TLS symbols in ELF was changed from ST_Data to
ST_Other in the following commit:
018a484cd26d72fb4c9e7fd75e5f5bc7838dfc73

RuntimeDyldELF::processRelocationRef() needs to be updated to also
handle ST_Other symbols so that it handles TLS relocations correctly.
The current tests did not fail because we have a shortcut for global
symbols that are already defined.

[lhames]

LGTM.

llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldELF.cpp

case SymbolRef::ST_Debug: {
         Value.SectionID = *SectionIDOrErr;
       else
         return SectionIDOrErr.takeError();
       Value.Addend = Addend;
       break;
     }
     case SymbolRef::ST_Data:
     case SymbolRef::ST_Function:
+    case SymbolRef::ST_Other:
     case SymbolRef::ST_Unknown: {
       Value.SymbolName = TargetName.data();
       Value.Addend = Addend;
 
       // Absolute relocations will have a zero symbol ID (STN_UNDEF), which
       // will manifest here as a NULL symbol name.
       // We can set this as a valid (but empty) symbol name, and rely
       // on addRelocationForSymbol to handle this.

llvm/test/ExecutionEngine/RuntimeDyld/X86/TLS.s

 # REQUIRES: x86_64-linux
 # RUN: rm -rf %t && mkdir -p %t
-# RUN: llvm-mc -triple=x86_64-unknown-linux -filetype=obj -o %t/tls.o %s
-# RUN: llvm-rtdyld -triple=x86_64-unknown-linux -execute %t/tls.o
+# RUN: split-file %s %t
+# RUN: llvm-mc -triple=x86_64-unknown-linux -filetype=obj -o %t/test_runner.o %t/test_runner.s
+# RUN: llvm-mc -triple=x86_64-unknown-linux -filetype=obj -o %t/external_tls.o %t/external_tls.s
+# RUN: llvm-rtdyld -triple=x86_64-unknown-linux -execute %t/test_runner.o %t/external_tls.o
 
+#--- test_runner.s
 
 _main:
 
   push %rbx
   # load the address of the GOT in rbx for the large code model tests
   lea _GLOBAL_OFFSET_TABLE_(%rip), %rbx
 
 # Test Local Exec TLS Model
1:
   call *%rax
   mov (%rax), %eax
   cmp $0x34, %eax
   je 1f
   mov $12, %eax
   jmp 2f
 1:
 
+# External TLS variable, Local Exec TLS Model (small code model)
+  mov %fs:external_tls_var@tpoff, %eax
+  cmp $0x56, %eax
+  je 1f
+  mov $12, %eax
+  jmp 2f
+1:
+
+# External TLS variable, Global Dynamic TLS Model (small code model)
+  .byte 0x66
+  leaq external_tls_var@tlsgd(%rip), %rdi
+  .byte 0x66, 0x66, 0x48
+  call __tls_get_addr@plt
+  mov (%rax), %eax
+  cmp $0x56, %eax
+  je 1f
+  mov $13, %eax
+  jmp 2f
+1:
+
+
+# Return 0 if all tests are successful
   xor %eax, %eax
 
 2:
   pop %rbx
   ret
 
 
   .section .tdata, "awT", @progbits
 
   .global tls_foo
   .type tls_foo, @object
   .size tls_foo, 4
   .align 4
 tls_foo:
   .long 0x12
 
   .global tls_bar
   .type tls_bar, @object
   .size tls_bar, 4
   .align 4
 tls_bar:
   .long 0x34
+
+#--- external_tls.s
+
+  .section .tdata, "awT", @progbits
+
+  .global external_tls_var
+  .type external_tls_var, @object
+  .size external_tls_var, 4
+  .align 4
+external_tls_var:
+  .long 0x56