CodeGen: support an extension to pass linker options on ELF

Introduce an extension to support passing linker options to the linker.
These would be ignored by older linkers, but newer linkers which support
this feature would be able to process the linker.

Emit a special discarded section `.linker-option`.  The content of this
section is a pair of strings (key, value).  The key is a type identifier for
the parameter.  This allows for an argument free parameter that will be
processed by the linker with the value being the parameter.  As an example,
`lib` identifies a library to be linked against, traditionally the `-l`
argument for Unix-based linkers with the parameter being the library name.

Thanks to James Henderson, Cary Coutant, Rafael Espinolda, Sean Silva
for the valuable discussion on the design of this feature.

llvm-svn: 323783

1 files changed, 18 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
index 0e90df901fd..dc3efe1d4bc 100644
--- a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
+++ b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
@@ -93,6 +93,24 @@ static void GetObjCImageInfo(Module &M, unsigned &Version, unsigned &Flags,
 
 void TargetLoweringObjectFileELF::emitModuleMetadata(
     MCStreamer &Streamer, Module &M, const TargetMachine &TM) const {
+  auto &C = getContext();
+
+  if (NamedMDNode *LinkerOptions = M.getNamedMetadata("llvm.linker.options")) {
+    auto *S = C.getELFSection(".linker-options", ELF::SHT_LLVM_LINKER_OPTIONS,
+                              ELF::SHF_EXCLUDE);
+
+    Streamer.SwitchSection(S);
+
+    for (const auto &Operand : LinkerOptions->operands()) {
+      if (cast<MDNode>(Operand)->getNumOperands() != 2)
+        report_fatal_error("invalid llvm.linker.options");
+      for (const auto &Option : cast<MDNode>(Operand)->operands()) {
+        Streamer.EmitBytes(cast<MDString>(Option)->getString());
+        Streamer.EmitIntValue(0, 1);
+      }
+    }
+  }
+
   unsigned Version = 0;
   unsigned Flags = 0;
   StringRef Section;
@@ -101,7 +119,6 @@ void TargetLoweringObjectFileELF::emitModuleMetadata(
   if (Section.empty())
     return;
 
-  auto &C = getContext();
   auto *S = C.getELFSection(Section, ELF::SHT_PROGBITS, ELF::SHF_ALLOC);
   Streamer.SwitchSection(S);
   Streamer.EmitLabel(C.getOrCreateSymbol(StringRef("OBJC_IMAGE_INFO")));