[lld-macho] Fix alignment of TLV data sections

[glandium]

Applied clang-format.

[glandium]

lld/test/MachO/tlv.s

129–132

Note that this doesn't cause a problem at an alignment of 16 unless __thread_vars has an odd number of entries, which makes (otherwise __thread_data is accidentally aligned to 16)

[int3]

Can you include a description of the problem in the commit message? (Just copying the block comment is fine)

lld/MachO/Writer.cpp

916

918

919

919–923

convention is to omit braces for one-liners

[glandium]

Addressed comments and added a check that __thread_vars is aligned correctly for the test to be valuable.

[glandium]

@int3 Can you commit this for me?

lld/MachO/Writer.cpp

static void sortSegmentsAndSections() {
   sortOutputSegments();
 
   DenseMap<const InputSection *, size_t> isecPriorities =
       buildInputSectionPriorities();
 
   uint32_t sectionIndex = 0;
   for (OutputSegment *seg : outputSegments) {
     seg->sortOutputSections();
+    // References from thread-local variable sections are treated as offsets
+    // relative to the start of the thread-local data memory area, which
+    // is initialized via copying all the TLV data sections (which are all
+    // contiguous). If later data sections require a greater alignment than
+    // earlier ones, the offsets of data within those sections won't be
+    // guaranteed to aligned unless we normalize alignments. We therefore use
+    // the largest alignment for all TLV data sections.
+    uint32_t tlvAlign = 0;
+    for (const OutputSection *osec : seg->getSections())
+      if (isThreadLocalData(osec->flags) && osec->align > tlvAlign)
+        tlvAlign = osec->align;
+
     for (OutputSection *osec : seg->getSections()) {
       // Now that the output sections are sorted, assign the final
       // output section indices.
       if (!osec->isHidden())
         osec->index = ++sectionIndex;
-      if (!firstTLVDataSection && isThreadLocalData(osec->flags))
+      if (isThreadLocalData(osec->flags)) {
+        if (!firstTLVDataSection)
           firstTLVDataSection = osec;
+        osec->align = tlvAlign;
+      }
 
       if (!isecPriorities.empty()) {
         if (auto *merged = dyn_cast<ConcatOutputSection>(osec)) {
           llvm::stable_sort(merged->inputs,
                             [&](InputSection *a, InputSection *b) {
                               return isecPriorities[a] > isecPriorities[b];
                             });
         }

lld/test/MachO/tlv.s

 # RUN: llvm-objdump -d --bind --rebase %t/tbss | FileCheck %s --check-prefixes=TBSS,LINKEDIT
 # RUN: llvm-objdump --macho --section=__DATA,__thread_vars %t/tbss | \
 # RUN:   FileCheck %s --check-prefix=TBSS-TLVP
 
 # RUN: %lld -lSystem %t/regular.o %t/tbss.o -o %t/regular-and-tbss
 # RUN: llvm-objdump -d --bind --rebase %t/regular-and-tbss | FileCheck %s --check-prefixes=REG,TBSS,LINKEDIT
 # RUN: llvm-objdump --macho --section=__DATA,__thread_vars %t/regular-and-tbss | \
 # RUN:   FileCheck %s --check-prefix=REG-TBSS-TLVP
-# RUN: llvm-objdump --section-headers %t/regular-and-tbss | FileCheck %s --check-prefix=SECTION-ORDER
+# RUN: llvm-objdump --section-headers %t/regular-and-tbss | FileCheck %s --check-prefix=SECTIONS
 
 ## Check that we always put __thread_bss immediately after __thread_data,
 ## regardless of the order of the input files.
 # RUN: %lld -lSystem %t/tbss.o %t/regular.o -o %t/regular-and-tbss
-# RUN: llvm-objdump --section-headers %t/regular-and-tbss | FileCheck %s --check-prefix=SECTION-ORDER
+# RUN: llvm-objdump --section-headers %t/regular-and-tbss | FileCheck %s --check-prefix=SECTIONS
 
 # HEADER: MH_HAS_TLV_DESCRIPTORS
 
 # REG:       <_main>:
 # REG-NEXT:  leaq    {{.*}}(%rip), %rax  ## {{.*}} <_foo>
 # REG-NEXT:  leaq    {{.*}}(%rip), %rax  ## {{.*}} <_bar>
 # REG-NEXT:  retq
 
 # TBSS:       <_f>:
 # TBSS-NEXT:  leaq    {{.*}}(%rip), %rax  ## {{.*}} <_baz>
 # TBSS-NEXT:  leaq    {{.*}}(%rip), %rax  ## {{.*}} <_qux>
+# TBSS-NEXT:  leaq    {{.*}}(%rip), %rax  ## {{.*}} <_hoge>
 # TBSS-NEXT:  retq
 
 # REG-TLVP:      00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 # REG-TLVP-NEXT: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 # REG-TLVP-NEXT: 00 00 00 00 00 00 00 00 08 00 00 00 00 00 00 00
 
 # TBSS-TLVP:      00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 # TBSS-TLVP-NEXT: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 # TBSS-TLVP-NEXT: 00 00 00 00 00 00 00 00 08 00 00 00 00 00 00 00
 
 # REG-TBSS-TLVP:      00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 # REG-TBSS-TLVP-NEXT: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
-# REG-TBSS-TLVP-NEXT: 00 00 00 00 00 00 00 00 08 00 00 00 00 00 00 00
+# REG-TBSS-TLVP-NEXT: 00 00 00 00 00 00 00 00 10 00 00 00 00 00 00 00
 # REG-TBSS-TLVP-NEXT: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
-# REG-TBSS-TLVP-NEXT: 10 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
-# REG-TBSS-TLVP-NEXT: 00 00 00 00 00 00 00 00 18 00 00 00 00 00 00 00
+# REG-TBSS-TLVP-NEXT: 20 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
+# REG-TBSS-TLVP-NEXT: 00 00 00 00 00 00 00 00 28 00 00 00 00 00 00 00
+# REG-TBSS-TLVP-NEXT: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
+# REG-TBSS-TLVP-NEXT: 30 00 00 00 00 00 00 00
 
 ## Make sure we don't emit rebase opcodes for relocations in __thread_vars.
 # LINKEDIT:       Rebase table:
 # LINKEDIT-NEXT:  segment  section            address     type
 # LINKEDIT-EMPTY:
 # LINKEDIT-NEXT:  Bind table:
 # LINKEDIT:       __DATA  __thread_vars   0x{{[0-9a-f]*}}  pointer 0 libSystem __tlv_bootstrap
 # LINKEDIT:       __DATA  __thread_vars   0x{{[0-9a-f]*}}  pointer 0 libSystem __tlv_bootstrap
 
-# SECTION-ORDER:      __thread_data
-# SECTION-ORDER:      more_thread_data
-# SECTION-ORDER-NEXT: __thread_bss
+## Make sure we have an odd number of tlv vars, and that the __thread_vars
+## section starts 16-bytes aligned. This is the setup required for __thread_data
+## not to be automatically 16-bytes aligned, ensuring the linker does its
+## expected job of aligning _hoge$tlv$init.
+# SECTIONS:      __thread_vars {{[0-9]+}}8 {{[0-9]+}}0
+# SECTIONS:      __thread_data
+# SECTIONS:      more_thread_data
+# SECTIONS-NEXT: __thread_bss
 
 #--- regular.s
 .globl _main
 _main:
   mov _foo@TLVP(%rip), %rax
   mov _bar@TLVP(%rip), %rax
   ret
 
_bar:
   .quad  _bar$tlv$init
 
 #--- tbss.s
 
 .globl _f
 _f:
   mov _baz@TLVP(%rip), %rax
   mov _qux@TLVP(%rip), %rax
+  mov _hoge@TLVP(%rip), %rax
   ret
 
 .tbss _baz$tlv$init, 8, 3
 .tbss _qux$tlv$init, 8, 3
+.tbss _hoge$tlv$init, 16, 4
 
 .section __DATA,__thread_vars,thread_local_variables
 _baz:
   .quad  __tlv_bootstrap
   .quad  0
   .quad  _baz$tlv$init
 _qux:
   .quad  __tlv_bootstrap
   .quad  0
   .quad  _qux$tlv$init
+_hoge:
+  .quad  __tlv_bootstrap
+  .quad  0
+  .quad  _hoge$tlv$init