Don't create a dummy __tls_get_addr

[• rafael]

Summary

We just don't need one with the current setup.

We only error on undefined references that are used by some relocation.

If we managed to relax all uses of __tls_get_addr, no relocation uses it and we don't produce an error.

This is less code and fixes the case were we fail to relax. Before we would produce a broken output, but now we produce an error.

[peter.smith]

I think that this is the right thing to do. On Arm and Mips there is no TLS relaxation so we can have a reference to __tls_get_addr at static link time that isn't removed, however the static libraries for these platforms do provide a definition. At the time of implementation in D25978 we had special cases to not add this symbol on Arm and Mips, I don't remember when these were deleted.

[ruiu]

LGTM

[• espindola]

315334

ELF/Writer.cpp

template <class ELFT> void Writer<ELFT>::addReservedSymbols() {
   // The _GLOBAL_OFFSET_TABLE_ symbol is defined by target convention to
   // be at some offset from the base of the .got section, usually 0 or the end
   // of the .got
   InputSection *GotSection = InX::MipsGot ? cast<InputSection>(InX::MipsGot)
                                           : cast<InputSection>(InX::Got);
   ElfSym::GlobalOffsetTable = addOptionalRegular<ELFT>(
       "_GLOBAL_OFFSET_TABLE_", GotSection, Target->GotBaseSymOff);
 
-  // __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.
-  if (!InX::DynSymTab)
-    if (SymbolBody *S = Symtab->find("__tls_get_addr"))
-      if (!S->isInCurrentDSO())
-        Symtab->addAbsolute<ELFT>(S->getName(), STV_HIDDEN);
-
   // __ehdr_start is the location of ELF file headers. Note that we define
   // this symbol unconditionally even when using a linker script, which
   // differs from the behavior implemented by GNU linker which only define
   // this symbol if ELF headers are in the memory mapped segment.
   // __executable_start is not documented, but the expectation of at
   // least the android libc is that it points to the elf header too.
   // __dso_handle symbol is passed to cxa_finalize as a marker to identify
   // each DSO. The address of the symbol doesn't matter as long as they are

test/ELF/arm-tls-norelax-gd-le.s

 x:
  .space 4
  .type  x, %object
 
 // CHECK:       Contents of section .got:
 // Module index is always 1 for executable
 // CHECK-NEXT:  13060 01000000 00000000
 
+
+// Without any definition of __tls_get_addr we get an error
+// RUN: not ld.lld  %t.o -o %t 2>&1 | FileCheck --check-prefix=ERR %s
+// ERR: error: undefined symbol: __tls_get_addr

test/ELF/tls-static.s

 // RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t
 // RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %S/Inputs/shared.s -o %tso
 // RUN: ld.lld -static %t -o %tout
 // RUN: ld.lld %t -o %tout
 // RUN: ld.lld -shared %tso -o %tshared
-// RUN: not ld.lld -static %t %tshared -o %tout 2>&1 | FileCheck %s
+// RUN: ld.lld -static %t %tshared -o %tout
 // REQUIRES: x86
 
 .global _start
 _start:
-  call __tls_get_addr
+  data16
+  leaq  foobar@TLSGD(%rip), %rdi
+  data16
+  data16
+  rex64
+  callq  __tls_get_addr@PLT
 
-// CHECK: error: undefined symbol: __tls_get_addr
-// CHECK: >>> referenced by {{.*}}:(.text+0x1)
+
+.section        .tdata,"awT",@progbits
+.global  foobar
+foobar:
+  .long   42