[lld-macho] Don't emit rebase opcodes for relocs in TLV sections

[int3]

Summary

Their addresses are already encoded as section-relative offsets, so
there's no need to rebase them at runtime. D85080: [lld-macho] Support static linking of thread-locals has some context
on the weirdness of TLV sections.

Fixes llvm.org/PR48491.

[thakis]

I suppose this corresponds to http://llvm-cs.pcc.me.uk/tools/lld/lib/ReaderWriter/MachO/ArchHandler_x86_64.cpp#457 ?

[int3]

Looks like it, yup

[int3]

don't forget to emit binding for __tlv_bootstrap

lld/MachO/Arch/X86_64.cpp

void X86_64::prepareSymbolRelocation(lld::macho::Symbol *sym,
   case X86_64_RELOC_UNSIGNED: {
     if (auto *dysym = dyn_cast<DylibSymbol>(sym)) {
       if (r.length != 3) {
         error("X86_64_RELOC_UNSIGNED referencing the dynamic symbol " +
               dysym->getName() + " must have r_length = 3");
         return;
       }
     }
+    // References from thread-local variable sections are treated as offsets
+    // relative to the start of the referent section, and therefore have no
+    // need of rebase opcodes.
+    if (!(isThreadLocalVariables(isec->flags) && isa<Defined>(sym)))
       addNonLazyBindingEntries(sym, isec, r.offset, r.addend);
     break;
   }
   case X86_64_RELOC_SIGNED:
   case X86_64_RELOC_SIGNED_1:
   case X86_64_RELOC_SIGNED_2:
   case X86_64_RELOC_SIGNED_4:
     // TODO: warn if they refer to a weak global
     break;

lld/test/MachO/tlv-dylib.s

 # REQUIRES: x86
 # RUN: split-file %s %t
 
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/libtlv.s -o %t/libtlv.o
 # RUN: %lld -dylib -install_name @executable_path/libtlv.dylib \
 # RUN:   -lSystem -o %t/libtlv.dylib %t/libtlv.o
-# RUN: llvm-objdump --exports-trie -d --no-show-raw-insn %t/libtlv.dylib | FileCheck %s --check-prefix=DYLIB
+# RUN: llvm-objdump --macho --exports-trie --rebase %t/libtlv.dylib | \
+# RUN:   FileCheck %s --check-prefix=DYLIB
 # DYLIB-DAG: _foo [per-thread]
 # DYLIB-DAG: _bar [per-thread]
+## Make sure we don't emit rebase opcodes for relocations in __thread_vars.
+# DYLIB:       Rebase table:
+# DYLIB-NEXT:  segment  section            address     type
+# DYLIB-EMPTY:
 
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/test.s -o %t/test.o
 # RUN: %lld -lSystem -L%t -ltlv %t/test.o -o %t/test
 # RUN: llvm-objdump --bind -d --no-show-raw-insn %t/test | FileCheck %s
 
 # CHECK:      movq [[#]](%rip), %rax # [[#%x, FOO:]]
 # CHECK-NEXT: movq [[#]](%rip), %rax # [[#%x, BAR:]]
 # CHECK-NEXT: movq [[#]](%rip), %rax # [[#%x, BAZ:]]

lld/test/MachO/tlv.s

 # REQUIRES: x86
 # RUN: mkdir -p %t
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t/test.o
+
 # RUN: %lld -lSystem -o %t/test %t/test.o
 # RUN: llvm-readobj --file-headers %t/test | FileCheck %s --check-prefix=HEADER
-# RUN: llvm-objdump -D %t/test | FileCheck %s
+# RUN: llvm-objdump -D --bind --rebase %t/test | FileCheck %s
+
+# RUN: %lld -lSystem -pie -o %t/test %t/test.o
+# RUN: llvm-readobj --file-headers %t/test | FileCheck %s --check-prefix=HEADER
+# RUN: llvm-objdump -D --bind --rebase %t/test | FileCheck %s
 
 # HEADER: MH_HAS_TLV_DESCRIPTORS
 
 # CHECK:       Disassembly of section __TEXT,__text:
 # CHECK-EMPTY:
 # CHECK-NEXT:  <_main>:
 # CHECK-NEXT:  leaq    {{.*}}(%rip), %rax  # {{.*}} <_foo>
 # CHECK-NEXT:  leaq    {{.*}}(%rip), %rax  # {{.*}} <_bar>

 # CHECK-EMPTY:
 # CHECK-NEXT:  <_bar>:
 # CHECK-NEXT:          ...
 # CHECK-NEXT:  04 00
 # CHECK-NEXT:  00 00
 # CHECK-NEXT:  00 00
 # CHECK-NEXT:  00 00
 
+## Make sure we don't emit rebase opcodes for relocations in __thread_vars.
+# CHECK:       Rebase table:
+# CHECK-NEXT:  segment  section            address     type
+# CHECK-NEXT:  Bind table:
+# CHECK:       __DATA  __thread_vars   0x{{[0-9a-f]*}}  pointer 0 libSystem __tlv_bootstrap
+# CHECK:       __DATA  __thread_vars   0x{{[0-9a-f]*}}  pointer 0 libSystem __tlv_bootstrap
+
 .globl _main
 _main:
   mov _foo@TLVP(%rip), %rax
   mov _bar@TLVP(%rip), %rax
   ret
 
 .section  __DATA,__thread_data,thread_local_regular
 _foo$tlv$init: