[ELF] - Do not add ignored absolute __tls_get_addr symbol for relocatable output.

[grimar]

Summary

This was the reason of PR30984:

cad/iverilog fail to link under FreeBSD with next error:
/usr/bin/ld: error: relocation R_X86_64_PLT32 cannot refer to absolute symbol __tls_get_addr

We should not convert undefined symbol to absolute, but that was done for -r.

[ruiu]

Actually, we shouldn't add not only __tls_get_addr but most of the synthetic symbols, no?

[grimar]

In D26545#593017, @ruiu wrote:

Actually, we shouldn't add not only __tls_get_addr but most of the synthetic symbols, no?

Sure, but that is a subject for another patches (queued in my todo list).
Do you mean you prefer fix them all at once ? IMHO we should be able to land this separately as it is
isolated and unblocks few ports.

[grimar]

Abandoned in favour of D26600.

ELF/Writer.cpp

template <class ELFT> void Writer<ELFT>::addReservedSymbols() {
   if (!Config->Relocatable)
     Symtab<ELFT>::X->addIgnored("_GLOBAL_OFFSET_TABLE_");
 
   // __tls_get_addr is defined by the dynamic linker for dynamic ELFs. For
   // static linking the linker is required to optimize away any references to
   // __tls_get_addr, so it's not defined anywhere. Create a hidden definition
   // to avoid the undefined symbol error. As usual special cases are ARM and
   // MIPS - the libc for these targets defines __tls_get_addr itself because
-  // there are no TLS optimizations for these targets.
-  if (!Out<ELFT>::DynSymTab &&
+  // there are no TLS optimizations for these targets. Relocatable output does
+  // not need that either.
+  if (!Config->Relocatable && !Out<ELFT>::DynSymTab &&
       (Config->EMachine != EM_MIPS && Config->EMachine != EM_ARM))
     Symtab<ELFT>::X->addIgnored("__tls_get_addr");
 
   // If linker script do layout we do not need to create any standart symbols.
   if (ScriptConfig->HasSections)
     return;
 
   ElfSym<ELFT>::EhdrStart = Symtab<ELFT>::X->addIgnored("__ehdr_start");

test/ELF/Inputs/relocatable-tls.s

+callq __tls_get_addr@PLT

test/ELF/relocatable-tls.s

+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t1.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux \
+# RUN:   %S/Inputs/relocatable-tls.s -o %t2.o
+
+# RUN: ld.lld -r %t2.o -o %t3.r
+# RUN: llvm-objdump -t %t3.r | FileCheck --check-prefix=RELOCATABLE %s
+# RELOCATABLE: SYMBOL TABLE:
+# RELOCATABLE: 0000000000000000 *UND* 00000000 __tls_get_addr
+
+# RUN: ld.lld -shared %t2.o %t3.r -o %t4.out
+# RUN: llvm-objdump -t %t4.out | FileCheck --check-prefix=DSO %s
+# DSO: SYMBOL TABLE:
+# DSO: 0000000000000000 *UND* 00000000 __tls_get_addr
+
+callq __tls_get_addr@PLT