[ELF] Implement .{ctors,dtors}.<priority> sections ordering

[atanasyan]

Summary

In general .ctors/.dtors sections might be considered as obsoleted but they still used on some target platforms like MIPS and maybe others.

Let's support ordering of such sections.

[shankarke]

Could you merge it with ArrayOrderPass ? what do you think ?

[atanasyan]

I abandon this revision. I plan to provide more complex and correct solution.

lib/ReaderWriter/ELF/CMakeLists.txt

 add_lld_library(lldELF
   ArrayOrderPass.cpp
+  CtorsOrderPass.cpp
   ELFLinkingContext.cpp
   Reader.cpp
   Writer.cpp
   )
 
 target_link_libraries(lldELF
   lldHexagonELFTarget
   lldMipsELFTarget

lib/ReaderWriter/ELF/CtorsOrderPass.h

+//===- lib/ReaderWriter/ELF/CtorsOrderPass.h ------------------------------===//
+//
+//                             The LLVM Linker
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLD_READER_WRITER_ELF_CTORS_ORDER_PASS_H
+#define LLD_READER_WRITER_ELF_CTORS_ORDER_PASS_H
+
+#include "lld/Core/Pass.h"
+
+namespace lld {
+namespace elf {
+/// \brief This pass sorts atoms in .{ctors,dtors}.<priority> sections.
+class CtorsOrderPass : public Pass {
+public:
+  void perform(std::unique_ptr<MutableFile> &mergedFile) override;
+};
+}
+}
+
+#endif

lib/ReaderWriter/ELF/CtorsOrderPass.cpp

+//===- lib/ReaderWriter/ELF/CtorsOrderPass.cpp ----------------------------===//
+//
+//                             The LLVM Linker
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "CtorsOrderPass.h"
+
+#include <algorithm>
+
+namespace lld {
+namespace elf {
+void CtorsOrderPass::perform(std::unique_ptr<MutableFile> &f) {
+  auto definedAtoms = f->definedAtoms();
+  std::stable_sort(definedAtoms.begin(), definedAtoms.end(),
+                   [](const DefinedAtom *left, const DefinedAtom *right) {
+    if (left->sectionChoice() != DefinedAtom::sectionCustomRequired ||
+        right->sectionChoice() != DefinedAtom::sectionCustomRequired)
+      return false;
+
+    StringRef leftSec = left->customSectionName();
+    StringRef rightSec = right->customSectionName();
+
+    // Both sections start with the same prefixes.
+    if (!(leftSec.startswith(".ctors") && rightSec.startswith(".ctors")) &&
+        !(leftSec.startswith(".dtors") && rightSec.startswith(".dtors")))
+      return false;
+
+    // Get priortiy
+    uint16_t leftPriority = 0;
+    leftSec.rsplit('.').second.getAsInteger(10, leftPriority);
+    uint16_t rightPriority = 0;
+    rightSec.rsplit('.').second.getAsInteger(10, rightPriority);
+
+    return leftPriority < rightPriority;
+  });
+}
+} // end namespace elf
+} // end namespace lld

lib/ReaderWriter/ELF/DefaultLayout.h

Layout::SectionOrder DefaultLayout<ELFT>::getSectionOrder(
   case DefinedAtom::typeConstant:
     return ORDER_RODATA;
 
   case DefinedAtom::typeData:
   case DefinedAtom::typeDataFast:
     return llvm::StringSwitch<Layout::SectionOrder>(name)
         .StartsWith(".init_array", ORDER_INIT_ARRAY)
         .StartsWith(".fini_array", ORDER_FINI_ARRAY)
+        .StartsWith(".ctors", ORDER_CTORS)
+        .StartsWith(".dtors", ORDER_DTORS)
         .Default(ORDER_DATA);
 
   case DefinedAtom::typeZeroFill:
   case DefinedAtom::typeZeroFillFast:
     return ORDER_BSS;
 
   case DefinedAtom::typeGOT:
     return llvm::StringSwitch<Layout::SectionOrder>(name)
return llvm::StringSwitch<StringRef>(da->customSectionName())
       .StartsWith(".gcc_except_table", ".gcc_except_table")
       .StartsWith(".data.rel.ro", ".data.rel.ro")
       .StartsWith(".data.rel.local", ".data.rel.local")
       .StartsWith(".data", ".data")
       .StartsWith(".tdata", ".tdata")
       .StartsWith(".tbss", ".tbss")
       .StartsWith(".init_array", ".init_array")
       .StartsWith(".fini_array", ".fini_array")
+      .StartsWith(".ctors", ".ctors")
+      .StartsWith(".dtors", ".dtors")
       .Default(da->customSectionName());
 }
 
 /// \brief Gets the segment for a output section
 template <class ELFT>
 Layout::SegmentType DefaultLayout<ELFT>::getSegmentType(
     Section<ELFT> *section) const {
 

lib/ReaderWriter/ELF/ELFLinkingContext.cpp

 //===- lib/ReaderWriter/ELF/ELFLinkingContext.cpp -------------------------===//
 //
 //                             The LLVM Linker
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #include "lld/ReaderWriter/ELFLinkingContext.h"
 
 #include "ArrayOrderPass.h"
+#include "CtorsOrderPass.h"
 #include "ELFFile.h"
 #include "TargetHandler.h"
 #include "Targets.h"
 
 #include "lld/Core/Instrumentation.h"
 #include "lld/Passes/LayoutPass.h"
 #include "lld/Passes/RoundTripYAMLPass.h"
 
bool ELFLinkingContext::isLittleEndian() const {
   // TODO: Do this properly. It is not defined purely by arch.
   return true;
 }
 
 void ELFLinkingContext::addPasses(PassManager &pm) {
   if (_runLayoutPass)
     pm.add(std::unique_ptr<Pass>(new LayoutPass(registry())));
   pm.add(std::unique_ptr<Pass>(new elf::ArrayOrderPass()));
+  pm.add(std::unique_ptr<Pass>(new elf::CtorsOrderPass()));
 }
 
 uint16_t ELFLinkingContext::getOutputMachine() const {
   switch (getTriple().getArch()) {
   case llvm::Triple::x86:
     return llvm::ELF::EM_386;
   case llvm::Triple::x86_64:
     return llvm::ELF::EM_X86_64;

test/elf/ctors-order.test

+# RUN: yaml2obj -format=elf %s > %t
+# RUN: lld -flavor gnu -target mipsel -shared %t --output-filetype=yaml \
+# RUN:   | FileCheck %s
+
+# CHECK:      defined-atoms:
+# CHECK-NEXT:    - type:            data
+# CHECK-NEXT:      content:         [ 11, 11, 11, 11 ]
+# CHECK-NEXT:      alignment:       2^2
+# CHECK-NEXT:      section-choice:  custom-required
+# CHECK-NEXT:      section-name:    .ctors.1
+# CHECK-NEXT:   - type:            data
+# CHECK-NEXT:      content:         [ 22, 22, 22, 22 ]
+# CHECK-NEXT:      alignment:       2^2
+# CHECK-NEXT:      section-choice:  custom-required
+# CHECK-NEXT:      section-name:    .ctors.2
+
+---
+FileHeader:
+  Class:           ELFCLASS32
+  Data:            ELFDATA2LSB
+  Type:            ET_REL
+  Machine:         EM_MIPS
+  Flags:           [ EF_MIPS_NOREORDER, EF_MIPS_CPIC,
+                     EF_MIPS_ABI_O32, EF_MIPS_ARCH_32 ]
+Sections:
+  - Name:            .ctors.2
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_WRITE, SHF_ALLOC ]
+    AddressAlign:    0x04
+    Content:         '22222222'
+  - Name:            .ctors.1
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_WRITE, SHF_ALLOC ]
+    AddressAlign:    0x04
+    Content:         '11111111'
+
+Symbols:
+  Local:
+    - Name:            .ctors.2
+      Type:            STT_SECTION
+      Section:         .ctors.2
+    - Name:            .ctors.1
+      Type:            STT_SECTION
+      Section:         .ctors.1
+...