Add support for writing HermitCore (https://hermitcore.org) ELF binaries.

HermitCore is a POSIX-compatible kernel for running a single application in
an isolated environment to get maximum performance and predictable runtime
behavior. It can either be used bare-metal on hardware or a VM (Unikernel)
or side by side to an existing Linux system (Multikernel).
Due to the latter feature, HermitCore binaries are marked with a different
OS ABI to let the Linux ELF loader distinguish them from regular Unix/Linux
binaries and load them using the HermitCore "proxy" tool.

Author: ColinFinck

include/llvm/ADT/Triple.h

@@ -182,7 +182,8 @@ class Triple {
     Mesa3D,
     Contiki,
     AMDPAL,     // AMD PAL Runtime
-    LastOSType = AMDPAL
+    HermitCore, // HermitCore Unikernel/Multikernel
+    LastOSType = HermitCore
   };
   enum EnvironmentType {
     UnknownEnvironment,

include/llvm/BinaryFormat/ELF.h

@@ -357,6 +357,7 @@ enum {
   ELFOSABI_AMDGPU_HSA = 64,    // AMD HSA runtime
   ELFOSABI_AMDGPU_PAL = 65,    // AMD PAL runtime
   ELFOSABI_AMDGPU_MESA3D = 66, // AMD GCN GPUs (GFX6+) for MESA runtime
+  ELFOSABI_HERMITCORE = 66,    // HermitCore Unikernel/Multikernel
   ELFOSABI_ARM = 97,           // ARM
   ELFOSABI_C6000_ELFABI = 64,  // Bare-metal TMS320C6000
   ELFOSABI_C6000_LINUX = 65,   // Linux TMS320C6000

include/llvm/MC/MCELFObjectWriter.h

@@ -73,6 +73,8 @@ class MCELFObjectTargetWriter : public MCObjectTargetWriter {
     switch (OSType) {
       case Triple::CloudABI:
         return ELF::ELFOSABI_CLOUDABI;
+      case Triple::HermitCore:
+        return ELF::ELFOSABI_HERMITCORE;
       case Triple::PS4:
       case Triple::FreeBSD:
         return ELF::ELFOSABI_FREEBSD;

lib/Support/Triple.cpp

@@ -209,6 +209,7 @@ StringRef Triple::getOSTypeName(OSType Kind) {
   case Mesa3D: return "mesa3d";
   case Contiki: return "contiki";
   case AMDPAL: return "amdpal";
+  case HermitCore: return "hermit";
   }
 
   llvm_unreachable("Invalid OSType");
@@ -502,6 +503,7 @@ static Triple::OSType parseOS(StringRef OSName) {
     .StartsWith("mesa3d", Triple::Mesa3D)
     .StartsWith("contiki", Triple::Contiki)
     .StartsWith("amdpal", Triple::AMDPAL)
+    .StartsWith("hermit", Triple::HermitCore)
     .Default(Triple::UnknownOS);
 }
 

tools/llvm-readobj/ELFDumper.cpp

@@ -868,6 +868,7 @@ static const EnumEntry<unsigned> ElfOSABI[] = {
   {"AROS",         "AROS",                 ELF::ELFOSABI_AROS},
   {"FenixOS",      "FenixOS",              ELF::ELFOSABI_FENIXOS},
   {"CloudABI",     "CloudABI",             ELF::ELFOSABI_CLOUDABI},
+  {"HermitCore",   "HermitCore",           ELF::ELFOSABI_HERMITCORE},
   {"Standalone",   "Standalone App",       ELF::ELFOSABI_STANDALONE}
 };
 

unittests/ADT/TripleTest.cpp

@@ -235,6 +235,12 @@ TEST(TripleTest, ParsedIDs) {
   EXPECT_EQ(Triple::Fuchsia, T.getOS());
   EXPECT_EQ(Triple::UnknownEnvironment, T.getEnvironment());
 
+  T = Triple("x86_64-unknown-hermit");
+  EXPECT_EQ(Triple::x86_64, T.getArch());
+  EXPECT_EQ(Triple::UnknownVendor, T.getVendor());
+  EXPECT_EQ(Triple::HermitCore, T.getOS());
+  EXPECT_EQ(Triple::UnknownEnvironment, T.getEnvironment());
+
   T = Triple("wasm32-unknown-unknown");
   EXPECT_EQ(Triple::wasm32, T.getArch());
   EXPECT_EQ(Triple::UnknownVendor, T.getVendor());