Add initial support for creating shared library with symbol versioning

This commit adds initial support for building shared libraries with
symbol versioning information. Symbol versioning allows to add version
information to symbols. It is used to provide multiple definitions of
the same symbol for backward compatibility.

This commit adds the support such that the functionality can be enabled
conditionally at build time by specifying ELD_ENABLE_SYMBOL_VERSIONING
CMake option. This commit also updates the PR checkin builder to enable
symbol versioning functionality.

Symbol versioning is a target-independent feature but requires support
from compiler, linker and the loader. From the ELF perspective, symbol
versioning is implemented using 3 sections:
.gnu.version(SHT_GNU_versym), .gnu.version_d(SHT_GNU_verdef), and
.gnu.version_r(SHT_GNU_verneed). This commit only provides support for
.gnu.version and .gnu.version_d sections because only they are required
when building a shared library. .gnu.version_r is required when using a
shared library. Briefly, these sections can be descrbed as:

- .gnu.version: An array of version IDs. i'th entry of this array stores
                the version ID of the i'th symbol in the dynamic symbol
                table.
- .gnu.version_d: Stores the version definitions of the symbols that
                  are defined by this module.
- .gnu.version_r: Stores the version definitions of the undefined symbols that
                  are used by this module.

To add the support for creating shared libraries with symbol versioning
information, this commit:
- Adds support for creating symbol versioning sections .gnu.version and
  .gnu.version_d
- Improve version script support to properly handle versioned
  nodes.
- Add logic to properly assign output version IDs to symbols.
- Update dynamic symbol table and .hash section to properly emit
  versioned symbols.
- Emit symbol versioning sections and correctly fill symbol versioning
  information in the .dynamic section.

Additionally, this commit adds the trace flag --trace=symbol-versioning.

Resolves #646

Signed-off-by: Parth Arora <[email protected]>

Author: parth-07

.github/workflows/ci.yml

@@ -89,6 +89,7 @@ jobs:
             -DLLVM_TARGETS_TO_BUILD="ARM;AArch64;RISCV;Hexagon;X86" \
             -DELD_TARGETS_TO_BUILD="ARM;AArch64;RISCV;Hexagon;x86_64" \
             -DCMAKE_BUILD_WITH_INSTALL_RPATH=ON \
+            -DELD_ENABLE_SYMBOL_VERSIONING=ON \
             ../llvm-project/llvm
 
       - name: Cache Usage before build

CMakeLists.txt

@@ -175,6 +175,11 @@ if(LLVM_USE_SANITIZER OR ELD_SANITIZE)
   endif()
 endif()
 
+option(ELD_ENABLE_SYMBOL_VERSIONING "Enable Eld symbol versioning support" OFF)
+if(ELD_ENABLE_SYMBOL_VERSIONING)
+  add_compile_definitions(ELD_ENABLE_SYMBOL_VERSIONING)
+endif()
+
 set(CMAKE_INCLUDE_CURRENT_DIR ON)
 include_directories(BEFORE ${CMAKE_CURRENT_BINARY_DIR}/include
                     ${CMAKE_CURRENT_SOURCE_DIR}/include)

cmake/modules/LITModules.cmake

@@ -59,6 +59,10 @@ function(generate_ext_lit ARCH OPTIONNAME LIT_CFG_PATH)
     "${CMAKE_CURRENT_BINARY_DIR}/llvm-lit-${ARCH_LOWER}-${OPTIONNAME}")
 endfunction()
 
+if(ELD_ENABLE_SYMBOL_VERSIONING)
+  set(ELD_ENABLE_SYMBOL_VERSIONING_TESTS "true")
+endif()
+
 function(add_eld_lit_cfg ARCH OPTION OPTIONNAME)
   set(ELD_CURRENT_TARGET "${ARCH}_${OPTIONNAME}")
   set(ELD_OPTION ${OPTION})

include/eld/Config/LinkerConfig.h

@@ -420,6 +420,12 @@ class LinkerConfig {
 
   std::string getSymDefString() const;
 
+  /// Returns true if the link should build a dynamic object file
+  /// or a dynamic executable file.
+#ifdef ELD_ENABLE_SYMBOL_VERSIONING
+  bool shouldBuildDynamicArtifact() const;
+#endif
+
 protected:
   CommandLineVectorT CommandLineVector;
 

include/eld/Core/Module.h

@@ -98,7 +98,10 @@ class Module {
     Trampoline,
     GlobalDataSymbols,
     GNUBuildID,
-    MAX,
+#ifdef ELD_ENABLE_SYMBOL_VERSIONING
+    SymbolVersioning,
+#endif
+    MAX
   } InternalInputType;
 
   typedef std::vector<InputFile *> ObjectList;

include/eld/Diagnostics/DiagCommonKinds.inc

@@ -83,7 +83,8 @@ DIAG(mismatched_group, DiagnosticEngine::Fatal,
 DIAG(unsupported_version_node, DiagnosticEngine::Warning,
      "Only anonymous version nodes are supported. Ignoring version script `%0'")
 DIAG(unsupported_dependent_node, DiagnosticEngine::Warning,
-     "Dependent nodes are not supported. Ignoring version script `%0'")
+     "Dependent nodes are not supported. Ignoring dependency for node '%0' "
+     "in version script '%1'")
 DIAG(unable_to_write_output_file, DiagnosticEngine::Error,
      "Unable to write output file %0 because of error %1")
 DIAG(unable_to_write_temporary_file, DiagnosticEngine::Fatal,

include/eld/Diagnostics/DiagSymbolVersioning.inc

@@ -0,0 +1,24 @@
+//===- DiagSymbolVersioning.inc--------------------------------------------===//
+// Part of the eld Project, under the BSD License
+// See https://github.com/qualcomm/eld/LICENSE.txt for license information.
+// SPDX-License-Identifier: BSD-3-Clause
+//===----------------------------------------------------------------------===//
+//
+//                     The MCLinker Project
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+DIAG(trace_creating_symbol_versioning_section, DiagnosticEngine::Trace,
+     "Creating symbol versioning section: %0")
+DIAG(trace_creating_symbol_versioning_fragment, DiagnosticEngine::Trace,
+     "Creating symbol versioning fragment: %0")
+DIAG(trace_version_script_matched_scope, DiagnosticEngine::Trace,
+     "Version script node matched %0 symbol '%1'")
+DIAG(trace_clear_export_due_to_local_scope, DiagnosticEngine::Trace,
+     "Clearing export for symbol '%0' due to local scope")
+DIAG(error_missing_version_node, DiagnosticEngine::Error,
+     "%0: symbol %1 has undefined version %2")
+DIAG(trace_assign_output_version_ids, DiagnosticEngine::Trace,
+     "Assigning version IDs to output symbols")

include/eld/Diagnostics/DiagnosticEngine.h

@@ -301,6 +301,7 @@ class Diag {
 #include "eld/Diagnostics/DiagRelocations.inc"
 #include "eld/Diagnostics/DiagStats.inc"
 #include "eld/Diagnostics/DiagSymbolResolutions.inc"
+#include "eld/Diagnostics/DiagSymbolVersioning.inc"
 #include "eld/Diagnostics/DiagTraceAssignments.inc"
 #include "eld/Diagnostics/DiagTraceFiles.inc"
 #include "eld/Diagnostics/DiagTraceGC.inc"

include/eld/Diagnostics/DiagnosticPrinter.h

@@ -47,6 +47,9 @@ class DiagnosticPrinter {
     TraceMergeStrings = 0x8000,
     TraceLinkerScript = 0x10000,
     TraceSymDef = 0x100000,
+#ifdef ELD_ENABLE_SYMBOL_VERSIONING
+    TraceSymbolVersioning = 0x200000
+#endif
   };
 
   enum Verbose : uint16_t { None = 0x0, Default = 0x1 };
@@ -98,6 +101,12 @@ class DiagnosticPrinter {
 
   bool traceSymDef() { return (Trace & TraceSymDef); }
 
+#ifdef ELD_ENABLE_SYMBOL_VERSIONING
+  bool traceSymbolVersioning() const { return (Trace & TraceSymbolVersioning); }
+#else
+  bool traceSymbolVersioning() const { return false; }
+#endif
+
   uint32_t trace() { return Trace; }
 
   uint32_t isVerbose() const { return VerboseLevel & Verbose::Default; }

include/eld/Driver/GnuLinkerOptions.td

@@ -688,7 +688,8 @@ defm trace
           "\t\t\t --trace=trampolines : trace trampolines\n"
           "\t\t\t --trace=wrap-symbols : trace symbol wrap options\n"
           "\t\t\t --trace=symdef : trace symbol resolution from symdef files\n"
-          "\t\t\t --trace=dynamic-linking : trace dynamic linking">,
+          "\t\t\t --trace=dynamic-linking : trace dynamic linking\n"
+          "\t\t\t --trace=symbol-versioning : trace symbol versioning">,
       MetaVarName<"<trace-type>">,
       Group<grp_diagopts>;
 defm trace_symbol : smDashTwoWithOpt<"y", "trace-symbol", "trace_symbol",