[ELF] Implement Dependent Libraries Feature

This patch implements a limited form of autolinking primarily designed to allow
either the --dependent-library compiler option, or "comment lib" pragmas (
https://docs.microsoft.com/en-us/cpp/preprocessor/comment-c-cpp?view=vs-2017) in
C/C++ e.g. #pragma comment(lib, "foo"), to cause an ELF linker to automatically
add the specified library to the link when processing the input file generated
by the compiler.

Currently this extension is unique to LLVM and LLD. However, care has been taken
to design this feature so that it could be supported by other ELF linkers.

The design goals were to provide:

- A simple linking model for developers to reason about.
- The ability to to override autolinking from the linker command line.
- Source code compatibility, where possible, with "comment lib" pragmas in other
  environments (MSVC in particular).

Dependent library support is implemented differently for ELF platforms than on
the other platforms. Primarily this difference is that on ELF we pass the
dependent library specifiers directly to the linker without manipulating them.
This is in contrast to other platforms where they are mapped to a specific
linker option by the compiler. This difference is a result of the greater
variety of ELF linkers and the fact that ELF linkers tend to handle libraries in
a more complicated fashion than on other platforms. This forces us to defer
handling the specifiers to the linker.

In order to achieve a level of source code compatibility with other platforms
we have restricted this feature to work with libraries that meet the following
"reasonable" requirements:

1. There are no competing defined symbols in a given set of libraries, or
   if they exist, the program owner doesn't care which is linked to their
   program.
2. There may be circular dependencies between libraries.

The binary representation is a mergeable string section (SHF_MERGE,
SHF_STRINGS), called .deplibs, with custom type SHT_LLVM_DEPENDENT_LIBRARIES
(0x6fff4c04). The compiler forms this section by concatenating the arguments of
the "comment lib" pragmas and --dependent-library options in the order they are
encountered. Partial (-r, -Ur) links are handled by concatenating .deplibs
sections with the normal mergeable string section rules. As an example, #pragma
comment(lib, "foo") would result in:

.section ".deplibs","MS",@llvm_dependent_libraries,1
         .asciz "foo"

For LTO, equivalent information to the contents of a the .deplibs section can be
retrieved by the LLD for bitcode input files.

LLD processes the dependent library specifiers in the following way:

1. Dependent libraries which are found from the specifiers in .deplibs sections
   of relocatable object files are added when the linker decides to include that
   file (which could itself be in a library) in the link. Dependent libraries
   behave as if they were appended to the command line after all other options. As
   a consequence the set of dependent libraries are searched last to resolve
   symbols.
2. It is an error if a file cannot be found for a given specifier.
3. Any command line options in effect at the end of the command line parsing apply
   to the dependent libraries, e.g. --whole-archive.
4. The linker tries to add a library or relocatable object file from each of the
   strings in a .deplibs section by; first, handling the string as if it was
   specified on the command line; second, by looking for the string in each of the
   library search paths in turn; third, by looking for a lib<string>.a or
   lib<string>.so (depending on the current mode of the linker) in each of the
   library search paths.
5. A new command line option --no-dependent-libraries tells LLD to ignore the
   dependent libraries.

Rationale for the above points:

1. Adding the dependent libraries last makes the process simple to understand
   from a developers perspective. All linkers are able to implement this scheme.
2. Error-ing for libraries that are not found seems like better behavior than
   failing the link during symbol resolution.
3. It seems useful for the user to be able to apply command line options which
   will affect all of the dependent libraries. There is a potential problem of
   surprise for developers, who might not realize that these options would apply
   to these "invisible" input files; however, despite the potential for surprise,
   this is easy for developers to reason about and gives developers the control
   that they may require.
4. This algorithm takes into account all of the different ways that ELF linkers
   find input files. The different search methods are tried by the linker in most
   obvious to least obvious order.
5. I considered adding finer grained control over which dependent libraries were
   ignored (e.g. MSVC has /nodefaultlib:<library>); however, I concluded that this
   is not necessary: if finer control is required developers can fall back to using
   the command line directly.

RFC thread: http://lists.llvm.org/pipermail/llvm-dev/2019-March/131004.html.

Differential Revision: https://reviews.llvm.org/D60274

llvm-svn: 360984

22 files changed, 179 insertions, 11 deletions

diff --git a/llvm/docs/Extensions.rst b/llvm/docs/Extensions.rst
index fac2289921e..8543ac61185 100644
--- a/llvm/docs/Extensions.rst
+++ b/llvm/docs/Extensions.rst
@@ -285,6 +285,26 @@ The following directives are specified:
     The paramter identifies an additional library search path to be considered
     when looking up libraries after the inclusion of this option.
 
+``SHT_LLVM_DEPENDENT_LIBRARIES`` Section (Dependent Libraries)
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This section contains strings specifying libraries to be added to the link by
+the linker.
+
+The section should be consumed by the linker and not written to the output.
+
+The strings are encoded as standard null-terminated UTF-8 strings.
+
+For example:
+
+.. code-block:: gas
+
+  .section ".deplibs","MS",@llvm_dependent_libraries,1
+  .asciz "library specifier 1"
+  .asciz "library specifier 2"
+
+The interpretation of the library specifiers is defined by the consuming linker.
+
 ``SHT_LLVM_CALL_GRAPH_PROFILE`` Section (Call Graph Profile)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
diff --git a/llvm/docs/LangRef.rst b/llvm/docs/LangRef.rst
index af6e484c4b8..bfe0a0ab9fe 100644
--- a/llvm/docs/LangRef.rst
+++ b/llvm/docs/LangRef.rst
@@ -6081,10 +6081,10 @@ enum is the smallest type which can represent all of its values::
 Automatic Linker Flags Named Metadata
 =====================================
 
-Some targets support embedding flags to the linker inside individual object
+Some targets support embedding of flags to the linker inside individual object
 files. Typically this is used in conjunction with language extensions which
-allow source files to explicitly declare the libraries they depend on, and have
-these automatically be transmitted to the linker via object files.
+allow source files to contain linker command line options, and have these
+automatically be transmitted to the linker via object files.
 
 These flags are encoded in the IR using named metadata with the name
 ``!llvm.linker.options``. Each operand is expected to be a metadata node
@@ -6095,8 +6095,8 @@ For example, the following metadata section specifies two separate sets of
 linker options, presumably to link against ``libz`` and the ``Cocoa``
 framework::
 
-    !0 = !{ !"-lz" },
-    !1 = !{ !"-framework", !"Cocoa" } } }
+    !0 = !{ !"-lz" }
+    !1 = !{ !"-framework", !"Cocoa" }
     !llvm.linker.options = !{ !0, !1 }
 
 The metadata encoding as lists of lists of options, as opposed to a collapsed
@@ -6109,6 +6109,28 @@ Each individual option is required to be either a valid option for the target's
 linker, or an option that is reserved by the target specific assembly writer or
 object file emitter. No other aspect of these options is defined by the IR.
 
+Dependent Libs Named Metadata
+=============================
+
+Some targets support embedding of strings into object files to indicate
+a set of libraries to add to the link. Typically this is used in conjunction
+with language extensions which allow source files to explicitly declare the
+libraries they depend on, and have these automatically be transmitted to the
+linker via object files.
+
+The list is encoded in the IR using named metadata with the name
+``!llvm.dependent-libraries``. Each operand is expected to be a metadata node
+which should contain a single string operand.
+
+For example, the following metadata section contains two library specfiers::
+
+    !0 = !{!"a library specifier"}
+    !1 = !{!"another library specifier"}
+    !llvm.dependent-libraries = !{ !0, !1 }
+
+Each library specifier will be handled independently by the consuming linker.
+The effect of the library specifiers are defined by the consuming linker.
+
 .. _summary:
 
 ThinLTO Summary
diff --git a/llvm/include/llvm-c/lto.h b/llvm/include/llvm-c/lto.h
index a22f0bbade4..5a33898d0f8 100644
--- a/llvm/include/llvm-c/lto.h
+++ b/llvm/include/llvm-c/lto.h
@@ -44,7 +44,7 @@ typedef bool lto_bool_t;
  * @{
  */
 
-#define LTO_API_VERSION 23
+#define LTO_API_VERSION 24
 
 /**
  * \since prior to LTO_API_VERSION=3
@@ -298,6 +298,14 @@ extern const char*
 lto_module_get_linkeropts(lto_module_t mod);
 
 /**
+* Returns the module's dependent library specifiers.
+*
+* \since LTO_API_VERSION=24
+*/
+extern const char*
+lto_module_get_dependent_libraries(lto_module_t mod);
+
+/**
  * Diagnostic severity.
  *
  * \since LTO_API_VERSION=7
diff --git a/llvm/include/llvm/BinaryFormat/ELF.h b/llvm/include/llvm/BinaryFormat/ELF.h
index 84f69666bb9..6ec924d08d1 100644
--- a/llvm/include/llvm/BinaryFormat/ELF.h
+++ b/llvm/include/llvm/BinaryFormat/ELF.h
@@ -841,6 +841,7 @@ enum : unsigned {
   SHT_LLVM_CALL_GRAPH_PROFILE = 0x6fff4c02, // LLVM Call Graph Profile.
   SHT_LLVM_ADDRSIG = 0x6fff4c03,        // List of address-significant symbols
                                         // for safe ICF.
+  SHT_LLVM_DEPENDENT_LIBRARIES = 0x6fff4c04, // LLVM Dependent Library Specifiers.
   // Android's experimental support for SHT_RELR sections.
   // https://android.googlesource.com/platform/bionic/+/b7feec74547f84559a1467aca02708ff61346d2a/libc/include/elf.h#512
   SHT_ANDROID_RELR = 0x6fffff00,        // Relocation entries; only offsets.
diff --git a/llvm/include/llvm/LTO/LTO.h b/llvm/include/llvm/LTO/LTO.h
index 76fa4f4dd62..d3a0d3c37dc 100644
--- a/llvm/include/llvm/LTO/LTO.h
+++ b/llvm/include/llvm/LTO/LTO.h
@@ -115,6 +115,7 @@ private:
   std::vector<std::pair<size_t, size_t>> ModuleSymIndices;
 
   StringRef TargetTriple, SourceFileName, COFFLinkerOpts;
+  std::vector<StringRef> DependentLibraries;
   std::vector<StringRef> ComdatTable;
 
 public:
@@ -155,6 +156,9 @@ public:
   /// Returns linker options specified in the input file.
   StringRef getCOFFLinkerOpts() const { return COFFLinkerOpts; }
 
+  /// Returns dependent library specifiers from the input file.
+  ArrayRef<StringRef> getDependentLibraries() const { return DependentLibraries; }
+
   /// Returns the path to the InputFile.
   StringRef getName() const;
 
diff --git a/llvm/include/llvm/LTO/legacy/LTOModule.h b/llvm/include/llvm/LTO/legacy/LTOModule.h
index 006521bf397..89d8682a207 100644
--- a/llvm/include/llvm/LTO/legacy/LTOModule.h
+++ b/llvm/include/llvm/LTO/legacy/LTOModule.h
@@ -47,6 +47,8 @@ private:
 
   std::string LinkerOpts;
 
+  std::string DependentLibraries;
+
   std::unique_ptr<Module> Mod;
   MemoryBufferRef MBRef;
   ModuleSymbolTable SymTab;
@@ -153,6 +155,8 @@ public:
 
   StringRef getLinkerOpts() { return LinkerOpts; }
 
+  StringRef getDependentLibraries() { return DependentLibraries; }
+
   const std::vector<StringRef> &getAsmUndefinedRefs() { return _asm_undefines; }
 
 private:
diff --git a/llvm/include/llvm/Object/IRSymtab.h b/llvm/include/llvm/Object/IRSymtab.h
index 0601d995fd1..0bbfc932493 100644
--- a/llvm/include/llvm/Object/IRSymtab.h
+++ b/llvm/include/llvm/Object/IRSymtab.h
@@ -125,12 +125,13 @@ struct Uncommon {
   Str SectionName;
 };
 
+
 struct Header {
   /// Version number of the symtab format. This number should be incremented
   /// when the format changes, but it does not need to be incremented if a
   /// change to LLVM would cause it to create a different symbol table.
   Word Version;
-  enum { kCurrentVersion = 1 };
+  enum { kCurrentVersion = 2 };
 
   /// The producer's version string (LLVM_VERSION_STRING " " LLVM_REVISION).
   /// Consumers should rebuild the symbol table from IR if the producer's
@@ -147,6 +148,9 @@ struct Header {
 
   /// COFF-specific: linker directives.
   Str COFFLinkerOpts;
+
+  /// Dependent Library Specifiers
+  Range<Str> DependentLibraries;
 };
 
 } // end namespace storage
@@ -231,6 +235,7 @@ class Reader {
   ArrayRef<storage::Comdat> Comdats;
   ArrayRef<storage::Symbol> Symbols;
   ArrayRef<storage::Uncommon> Uncommons;
+  ArrayRef<storage::Str> DependentLibraries;
 
   StringRef str(storage::Str S) const { return S.get(Strtab); }
 
@@ -251,6 +256,7 @@ public:
     Comdats = range(header().Comdats);
     Symbols = range(header().Symbols);
     Uncommons = range(header().Uncommons);
+    DependentLibraries = range(header().DependentLibraries);
   }
 
   using symbol_range = iterator_range<object::content_iterator<SymbolRef>>;
@@ -283,6 +289,16 @@ public:
 
   /// COFF-specific: returns linker options specified in the input file.
   StringRef getCOFFLinkerOpts() const { return str(header().COFFLinkerOpts); }
+
+  /// Returns dependent library specifiers
+  std::vector<StringRef> getDependentLibraries() const {
+    std::vector<StringRef> Specifiers;
+    Specifiers.reserve(DependentLibraries.size());
+    for (auto S : DependentLibraries) {
+      Specifiers.push_back(str(S));
+    }
+    return Specifiers;
+  }
 };
 
 /// Ephemeral symbols produced by Reader::symbols() and
diff --git a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
index 436076f33b9..b3aa8c6e634 100644
--- a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
+++ b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
@@ -271,6 +271,19 @@ void TargetLoweringObjectFileELF::emitModuleMetadata(MCStreamer &Streamer,
     }
   }
 
+  if (NamedMDNode *DependentLibraries = M.getNamedMetadata("llvm.dependent-libraries")) {
+    auto *S = C.getELFSection(".deplibs", ELF::SHT_LLVM_DEPENDENT_LIBRARIES,
+                              ELF::SHF_MERGE | ELF::SHF_STRINGS, 1, "");
+
+    Streamer.SwitchSection(S);
+
+    for (const auto &Operand : DependentLibraries->operands()) {
+      Streamer.EmitBytes(
+          cast<MDString>(cast<MDNode>(Operand)->getOperand(0))->getString());
+      Streamer.EmitIntValue(0, 1);
+    }
+  }
+
   unsigned Version = 0;
   unsigned Flags = 0;
   StringRef Section;
diff --git a/llvm/lib/LTO/LTO.cpp b/llvm/lib/LTO/LTO.cpp
index 442c0853263..ce1b0a1e4f6 100644
--- a/llvm/lib/LTO/LTO.cpp
+++ b/llvm/lib/LTO/LTO.cpp
@@ -425,6 +425,7 @@ Expected<std::unique_ptr<InputFile>> InputFile::create(MemoryBufferRef Object) {
   File->TargetTriple = FOrErr->TheReader.getTargetTriple();
   File->SourceFileName = FOrErr->TheReader.getSourceFileName();
   File->COFFLinkerOpts = FOrErr->TheReader.getCOFFLinkerOpts();
+  File->DependentLibraries = FOrErr->TheReader.getDependentLibraries();
   File->ComdatTable = FOrErr->TheReader.getComdatTable();
 
   for (unsigned I = 0; I != FOrErr->Mods.size(); ++I) {
diff --git a/llvm/lib/LTO/LTOModule.cpp b/llvm/lib/LTO/LTOModule.cpp
index eb46b31d211..83e9a09854c 100644
--- a/llvm/lib/LTO/LTOModule.cpp
+++ b/llvm/lib/LTO/LTOModule.cpp
@@ -646,5 +646,9 @@ void LTOModule::parseMetadata() {
     emitLinkerFlagsForGlobalCOFF(OS, Sym.symbol, TT, M);
   }
 
-  // Add other interesting metadata here.
+  // Dependent Libraries
+  raw_string_ostream OSD(DependentLibraries);
+  if (NamedMDNode *DependentLibraries = getModule().getNamedMetadata("llvm.dependent-libraries"))
+    for (MDNode *N : DependentLibraries->operands())
+      OSD << " " << cast<MDString>(N->getOperand(0))->getString();
 }
diff --git a/llvm/lib/MC/MCParser/ELFAsmParser.cpp b/llvm/lib/MC/MCParser/ELFAsmParser.cpp
index 9e5b54a6881..48ced8d3dfa 100644
--- a/llvm/lib/MC/MCParser/ELFAsmParser.cpp
+++ b/llvm/lib/MC/MCParser/ELFAsmParser.cpp
@@ -615,6 +615,8 @@ EndStmt:
       Type = ELF::SHT_LLVM_LINKER_OPTIONS;
     else if (TypeName == "llvm_call_graph_profile")
       Type = ELF::SHT_LLVM_CALL_GRAPH_PROFILE;
+    else if (TypeName == "llvm_dependent_libraries")
+      Type = ELF::SHT_LLVM_DEPENDENT_LIBRARIES;
     else if (TypeName.getAsInteger(0, Type))
       return TokError("unknown section type");
   }
diff --git a/llvm/lib/MC/MCSectionELF.cpp b/llvm/lib/MC/MCSectionELF.cpp
index e3c24efa93f..569b6ba0997 100644
--- a/llvm/lib/MC/MCSectionELF.cpp
+++ b/llvm/lib/MC/MCSectionELF.cpp
@@ -152,6 +152,8 @@ void MCSectionELF::PrintSwitchToSection(const MCAsmInfo &MAI, const Triple &T,
     OS << "llvm_linker_options";
   else if (Type == ELF::SHT_LLVM_CALL_GRAPH_PROFILE)
     OS << "llvm_call_graph_profile";
+  else if (Type == ELF::SHT_LLVM_DEPENDENT_LIBRARIES)
+    OS << "llvm_dependent_libraries";
   else
     report_fatal_error("unsupported type 0x" + Twine::utohexstr(Type) +
                        " for section " + getSectionName());
diff --git a/llvm/lib/Object/ELF.cpp b/llvm/lib/Object/ELF.cpp
index d5d98126343..951f4ae8f7e 100644
--- a/llvm/lib/Object/ELF.cpp
+++ b/llvm/lib/Object/ELF.cpp
@@ -253,6 +253,7 @@ StringRef llvm::object::getELFSectionTypeName(uint32_t Machine, unsigned Type) {
     STRINGIFY_ENUM_CASE(ELF, SHT_LLVM_LINKER_OPTIONS);
     STRINGIFY_ENUM_CASE(ELF, SHT_LLVM_CALL_GRAPH_PROFILE);
     STRINGIFY_ENUM_CASE(ELF, SHT_LLVM_ADDRSIG);
+    STRINGIFY_ENUM_CASE(ELF, SHT_LLVM_DEPENDENT_LIBRARIES);
     STRINGIFY_ENUM_CASE(ELF, SHT_GNU_ATTRIBUTES);
     STRINGIFY_ENUM_CASE(ELF, SHT_GNU_HASH);
     STRINGIFY_ENUM_CASE(ELF, SHT_GNU_verdef);
diff --git a/llvm/lib/Object/IRSymtab.cpp b/llvm/lib/Object/IRSymtab.cpp
index e80eaf1db32..e4282b9d6bd 100644
--- a/llvm/lib/Object/IRSymtab.cpp
+++ b/llvm/lib/Object/IRSymtab.cpp
@@ -89,6 +89,8 @@ struct Builder {
   std::string COFFLinkerOpts;
   raw_string_ostream COFFLinkerOptsOS{COFFLinkerOpts};
 
+  std::vector<storage::Str> DependentLibraries;
+
   void setStr(storage::Str &S, StringRef Value) {
     S.Offset = StrtabBuilder.add(Value);
     S.Size = Value.size();
@@ -140,6 +142,20 @@ Error Builder::addModule(Module *M) {
     }
   }
 
+  if (TT.isOSBinFormatELF()) {
+    if (auto E = M->materializeMetadata())
+      return E;
+    if (NamedMDNode *N = M->getNamedMetadata("llvm.dependent-libraries")) {
+      for (MDNode *MDOptions : N->operands()) {
+        const auto OperandStr =
+            cast<MDString>(cast<MDNode>(MDOptions)->getOperand(0))->getString();
+        storage::Str Specifier;
+        setStr(Specifier, OperandStr);
+        DependentLibraries.emplace_back(Specifier);
+      }
+    }
+  }
+
   for (ModuleSymbolTable::Symbol Msym : Msymtab.symbols())
     if (Error Err = addSymbol(Msymtab, Used, Msym))
       return Err;
@@ -312,7 +328,7 @@ Error Builder::build(ArrayRef<Module *> IRMods) {
   writeRange(Hdr.Comdats, Comdats);
   writeRange(Hdr.Symbols, Syms);
   writeRange(Hdr.Uncommons, Uncommons);
-
+  writeRange(Hdr.DependentLibraries, DependentLibraries);
   *reinterpret_cast<storage::Header *>(Symtab.data()) = Hdr;
   return Error::success();
 }
diff --git a/llvm/lib/ObjectYAML/ELFYAML.cpp b/llvm/lib/ObjectYAML/ELFYAML.cpp
index 1ac624fe958..39e59efe00f 100644
--- a/llvm/lib/ObjectYAML/ELFYAML.cpp
+++ b/llvm/lib/ObjectYAML/ELFYAML.cpp
@@ -455,6 +455,7 @@ void ScalarEnumerationTraits<ELFYAML::ELF_SHT>::enumeration(
   ECase(SHT_LLVM_LINKER_OPTIONS);
   ECase(SHT_LLVM_CALL_GRAPH_PROFILE);
   ECase(SHT_LLVM_ADDRSIG);
+  ECase(SHT_LLVM_DEPENDENT_LIBRARIES);
   ECase(SHT_GNU_ATTRIBUTES);
   ECase(SHT_GNU_HASH);
   ECase(SHT_GNU_verdef);
diff --git a/llvm/test/Feature/elf-deplibs.ll b/llvm/test/Feature/elf-deplibs.ll
new file mode 100644
index 00000000000..c44740ef961
--- /dev/null
+++ b/llvm/test/Feature/elf-deplibs.ll
@@ -0,0 +1,15 @@
+; RUN: llc -mtriple x86_64-elf -filetype asm -o - %s | FileCheck %s
+; REQUIRES: x86-registered-target
+
+!llvm.dependent-libraries = !{!0, !1, !0}
+
+!0 = !{!"foo"}
+!1 = !{!"b a r"}
+
+; CHECK: .section .deplibs,"MS",@llvm_dependent_libraries,1
+; CHECK-NEXT: .ascii  "foo"
+; CHECK-NEXT: .byte   0
+; CHECK-NEXT: .ascii  "b a r"
+; CHECK-NEXT: .byte   0
+; CHECK-NEXT: .ascii  "foo"
+; CHECK-NEXT: .byte   0
diff --git a/llvm/test/LTO/Resolution/X86/symtab-elf.ll b/llvm/test/LTO/Resolution/X86/symtab-elf.ll
index d5f0fbe3700..40864a82dd0 100644
--- a/llvm/test/LTO/Resolution/X86/symtab-elf.ll
+++ b/llvm/test/LTO/Resolution/X86/symtab-elf.ll
@@ -9,6 +9,12 @@ target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 !0 = !{!"/include:foo"}
 !llvm.linker.options = !{ !0 }
 
+; CHECK: {{^dependent libraries: \"foo\" \"b a r\" \"baz\"$}}
+!1 = !{!"foo"}
+!2 = !{!"b a r"}
+!3 = !{!"baz"}
+!llvm.dependent-libraries = !{!1, !2, !3}
+
 @g1 = global i32 0
 
 ; CHECK-NOT: fallback g1
diff --git a/llvm/test/MC/ELF/section.s b/llvm/test/MC/ELF/section.s
index d31909f5f42..7c9bb7915d1 100644
--- a/llvm/test/MC/ELF/section.s
+++ b/llvm/test/MC/ELF/section.s
@@ -293,3 +293,16 @@ bar:
 // CHECK-NEXT:   ]
 // CHECK: }
 
+// Test SHT_LLVM_DEPENDENT_LIBRARIES
+
+.section .deplibs,"MS",@llvm_dependent_libraries,1
+// ASM: .section .deplibs,"MS",@llvm_dependent_libraries,1
+
+// CHECK: Section {
+// CHECK:   Name: .deplibs
+// CHECK-NEXT:   Type: SHT_LLVM_DEPENDENT_LIBRARIES
+// CHECK-NEXT:   Flags [
+// CHECK-NEXT:       SHF_MERGE
+// CHECK-NEXT:       SHF_STRINGS
+// CHECK-NEXT:   ]
+// CHECK: }
diff --git a/llvm/test/Object/X86/irsymtab.ll b/llvm/test/Object/X86/irsymtab.ll
index 78e474df9a5..1b9915a2b74 100644
--- a/llvm/test/Object/X86/irsymtab.ll
+++ b/llvm/test/Object/X86/irsymtab.ll
@@ -9,16 +9,17 @@
 
 ; BCA:      <SYMTAB_BLOCK
 ; Version stored at offset 0.
-; BCA-NEXT:   <BLOB abbrevid=4/> blob data = '\x01\x00\x00\x00\x06\x00\x00\x00\x08\x00\x00\x00D\x00\x00\x00\x01\x00\x00\x00P\x00\x00\x00\x00\x00\x00\x00P\x00\x00\x00\x02\x00\x00\x00\x80\x00\x00\x00\x00\x00\x00\x00\x0E\x00\x00\x00\x18\x00\x00\x00&\x00\x00\x00\x0B\x00\x00\x001\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x03\x00\x00\x00\x00\x00\x00\x00\x03\x00\x00\x00\xFF\xFF\xFF\xFF\x00$\x00\x00\x03\x00\x00\x00\x03\x00\x00\x00\x03\x00\x00\x00\x03\x00\x00\x00\xFF\xFF\xFF\xFF\x08$\x00\x00'
+; BCA-NEXT:   <BLOB abbrevid=4/> blob data = '\x02\x00\x00\x00\x06\x00\x00\x00\x08\x00\x00\x00L\x00\x00\x00\x01\x00\x00\x00X\x00\x00\x00\x00\x00\x00\x00X\x00\x00\x00\x02\x00\x00\x00\x88\x00\x00\x00\x00\x00\x00\x00\x0E\x00\x00\x00\x18\x00\x00\x00&\x00\x00\x00\x0B\x00\x00\x001\x00\x00\x00\x00\x00\x00\x00\x88\x00\x00\x00\x02\x00\x00\x00\x00\x00\x00\x00\x02\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x03\x00\x00\x00\x00\x00\x00\x00\x03\x00\x00\x00\xFF\xFF\xFF\xFF\x00$\x00\x00\x03\x00\x00\x00\x03\x00\x00\x00\x03\x00\x00\x00\x03\x00\x00\x00\xFF\xFF\xFF\xFF\x08$\x00\x00\x00\x00\x00\x00\x03\x00\x00\x00\x03\x00\x00\x00\x03\x00\x00\x00'
 ; BCA-NEXT: </SYMTAB_BLOCK>
 ; BCA-NEXT: <STRTAB_BLOCK
 ; BCA-NEXT:   <BLOB abbrevid=4/> blob data = 'foobarproducerx86_64-unknown-linux-gnuirsymtab.ll'
 ; BCA-NEXT: </STRTAB_BLOCK>
 
-; SYMTAB:      version: 1
+; SYMTAB:      version: 2
 ; SYMTAB-NEXT: producer: producer
 ; SYMTAB-NEXT: target triple: x86_64-unknown-linux-gnu
 ; SYMTAB-NEXT: source filename: irsymtab.ll
+; SYMTAB-NEXT: {{^dependent libraries: \"foo\" \"bar\"$}}
 ; SYMTAB-NEXT: D------X foo
 ; SYMTAB-NEXT: DU-----X bar
 
@@ -31,3 +32,8 @@ define void @foo() {
 }
 
 declare void @bar()
+
+!llvm.dependent-libraries = !{!0, !1}
+
+!0 = !{!"foo"}
+!1 = !{!"bar"}
diff --git a/llvm/tools/llvm-lto2/llvm-lto2.cpp b/llvm/tools/llvm-lto2/llvm-lto2.cpp
index df51921396a..72d80f64a96 100644
--- a/llvm/tools/llvm-lto2/llvm-lto2.cpp
+++ b/llvm/tools/llvm-lto2/llvm-lto2.cpp
@@ -360,6 +360,13 @@ static int dumpSymtab(int argc, char **argv) {
     if (TT.isOSBinFormatCOFF())
       outs() << "linker opts: " << Input->getCOFFLinkerOpts() << '\n';
 
+    if (TT.isOSBinFormatELF()) {
+      outs() << "dependent libraries:";
+      for (auto L : Input->getDependentLibraries())
+        outs() << " \"" << L << "\"";
+      outs() << '\n';
+    }
+
     std::vector<StringRef> ComdatTable = Input->getComdatTable();
     for (const InputFile::Symbol &Sym : Input->symbols()) {
       switch (Sym.getVisibility()) {
diff --git a/llvm/tools/llvm-readobj/ELFDumper.cpp b/llvm/tools/llvm-readobj/ELFDumper.cpp
index ba6622686b9..75579879762 100644
--- a/llvm/tools/llvm-readobj/ELFDumper.cpp
+++ b/llvm/tools/llvm-readobj/ELFDumper.cpp
@@ -2857,6 +2857,8 @@ static std::string getSectionTypeString(unsigned Arch, unsigned Type) {
     return "LLVM_CALL_GRAPH_PROFILE";
   case SHT_LLVM_ADDRSIG:
     return "LLVM_ADDRSIG";
+  case SHT_LLVM_DEPENDENT_LIBRARIES:
+    return "LLVM_DEPENDENT_LIBRARIES";
   // FIXME: Parse processor specific GNU attributes
   case SHT_GNU_ATTRIBUTES:
     return "ATTRIBUTES";
diff --git a/llvm/tools/lto/lto.cpp b/llvm/tools/lto/lto.cpp
index 379b5b89714..01dc141ffd0 100644
--- a/llvm/tools/lto/lto.cpp
+++ b/llvm/tools/lto/lto.cpp
@@ -325,6 +325,10 @@ const char* lto_module_get_linkeropts(lto_module_t mod) {
   return unwrap(mod)->getLinkerOpts().data();
 }
 
+const char* lto_module_get_dependent_libraries(lto_module_t mod) {
+    return unwrap(mod)->getDependentLibraries().data();
+}
+
 void lto_codegen_set_diagnostic_handler(lto_code_gen_t cg,
                                         lto_diagnostic_handler_t diag_handler,
                                         void *ctxt) {