From 57ef51a040ed1efa68640c60dc52209a6202a04b Mon Sep 17 00:00:00 2001
From: Owen Anderson <resistor@mac.com>
Date: Wed, 20 Aug 2025 17:38:24 +0800
Subject: [PATCH] [CHERIoT] Wire up enough driver support to be able to
 successfully infer -mabi=cheriot from the cheriotrtos OS field in the triple.

---
 clang/lib/Driver/ToolChains/Arch/RISCV.cpp | 56 ++++++----------------
 llvm/lib/TargetParser/RISCVISAInfo.cpp     |  2 +
 2 files changed, 17 insertions(+), 41 deletions(-)

diff --git a/clang/lib/Driver/ToolChains/Arch/RISCV.cpp b/clang/lib/Driver/ToolChains/Arch/RISCV.cpp
index 19c1445a8e72c..89fed43cde286 100644
--- a/clang/lib/Driver/ToolChains/Arch/RISCV.cpp
+++ b/clang/lib/Driver/ToolChains/Arch/RISCV.cpp
@@ -63,6 +63,8 @@ static bool isCheriPurecapABIName(StringRef ABI) {
       .Case("l64pc128", true)
       .Case("l64pc128f", true)
       .Case("l64pc128d", true)
+      .Case("cheriot", true)
+      .Case("cheriot-baremetal", true)
       .Default(false);
 }
 
@@ -205,8 +207,12 @@ void riscv::getRISCVTargetFeatures(const Driver &D, const llvm::Triple &Triple,
                             options::OPT_m_riscv_Features_Group);
 
   if (Arg *A = Args.getLastArg(options::OPT_mabi_EQ)) {
-    bool IsPureCapability = isCheriPurecapABIName(A->getValue());
-    if (IsPureCapability) {
+    StringRef ABI = A->getValue();
+    bool IsPureCapability = isCheriPurecapABIName(ABI);
+    if (ABI == "cheriot" || ABI == "cheriot-baremetal") {
+      // +xcheriot implies both +xcheri and +xcheripurecap
+      Features.push_back("+xcheriot");
+    } else if (IsPureCapability) {
       auto ISAInfo = llvm::RISCVISAInfo::parseFeatures(
           Triple.isArch32Bit() ? 32 : 64,
           std::vector<std::string>(Features.begin(), Features.end()));
@@ -224,42 +230,6 @@ void riscv::getRISCVTargetFeatures(const Driver &D, const llvm::Triple &Triple,
     }
   }
 
-  if (Arg *A = Args.getLastArg(options::OPT_mabi_EQ)) {
-    bool IsPureCapability = isCheriPurecapABIName(A->getValue());
-    if (IsPureCapability) {
-      if (llvm::find(Features, "+xcheri") == Features.end()) {
-        D.Diag(diag::err_riscv_invalid_abi) << A->getValue()
-          << "pure capability ABI requires xcheri extension to be specified";
-        return;
-      }
-      Features.push_back("+xcheripurecap");
-    }
-  }
-
-  if (Arg *A = Args.getLastArg(options::OPT_mabi_EQ)) {
-    bool IsPureCapability = isCheriPurecapABIName(A->getValue());
-    if (IsPureCapability) {
-      if (llvm::find(Features, "+xcheri") == Features.end()) {
-        D.Diag(diag::err_riscv_invalid_abi) << A->getValue()
-          << "pure capability ABI requires xcheri extension to be specified";
-        return;
-      }
-      Features.push_back("+xcheripurecap");
-    }
-  }
-
-  if (Arg *A = Args.getLastArg(options::OPT_mabi_EQ)) {
-    bool IsPureCapability = isCheriPurecapABIName(A->getValue());
-    if (IsPureCapability) {
-      if (llvm::find(Features, "+xcheri") == Features.end()) {
-        D.Diag(diag::err_riscv_invalid_abi) << A->getValue()
-          << "pure capability ABI requires xcheri extension to be specified";
-        return;
-      }
-      Features.push_back("+xcheripurecap");
-    }
-  }
-
   // If -mstrict-align, -mno-strict-align, -mscalar-strict-align, or
   // -mno-scalar-strict-align is passed, use it. Otherwise, the
   // unaligned-scalar-mem is enabled if the CPU supports it or the target is
@@ -356,6 +326,8 @@ StringRef riscv::getRISCVABI(const ArgList &Args, const llvm::Triple &Triple) {
   // - On `riscv{XLEN}-unknown-elf` we use the integer calling convention only.
   // - On all other OSs we use the double floating point calling convention.
   if (Triple.isRISCV32()) {
+    if (Triple.getOS() == llvm::Triple::CheriotRTOS)
+      return "cheriot";
     if (Triple.getOS() == llvm::Triple::UnknownOS)
       return "ilp32";
     else
@@ -457,8 +429,9 @@ std::string riscv::getRISCVArch(const llvm::opt::ArgList &Args,
   // We deviate from GCC's defaults here:
   // - On `riscv{XLEN}-unknown-elf` we default to `rv{XLEN}imac`
   // - On all other OSs we use `rv{XLEN}imafdc` (equivalent to `rv{XLEN}gc`)
-  if (Triple.getSubArch() == llvm::Triple::RISCV32SubArch_cheriot_v1)
-    return "rv32emc_xcheri";
+  if (Triple.getSubArch() == llvm::Triple::RISCV32SubArch_cheriot_v1 ||
+      Triple.getOS() == llvm::Triple::CheriotRTOS)
+    return "rv32emc_xcheriot";
   if (Triple.isRISCV32()) {
     if (Triple.getOS() == llvm::Triple::UnknownOS)
       return "rv32imac";
@@ -488,7 +461,8 @@ std::string riscv::getRISCVTargetCPU(const llvm::opt::ArgList &Args,
   if (!CPU.empty())
     return CPU;
 
-  if (Triple.getSubArch() == llvm::Triple::RISCV32SubArch_cheriot_v1)
+  if (Triple.getOS() == llvm::Triple::CheriotRTOS ||
+      Triple.getSubArch() == llvm::Triple::RISCV32SubArch_cheriot_v1)
     return "cheriot";
 
   return Triple.isRISCV64() ? "generic-rv64" : "generic-rv32";
diff --git a/llvm/lib/TargetParser/RISCVISAInfo.cpp b/llvm/lib/TargetParser/RISCVISAInfo.cpp
index 17b8c2ac77307..5d012888740a9 100644
--- a/llvm/lib/TargetParser/RISCVISAInfo.cpp
+++ b/llvm/lib/TargetParser/RISCVISAInfo.cpp
@@ -957,6 +957,8 @@ RISCVISAInfo::postProcessAndChecking(std::unique_ptr<RISCVISAInfo> &&ISAInfo) {
 
 StringRef RISCVISAInfo::computeDefaultABI() const {
   if (XLen == 32) {
+    if (Exts.count("xcheriot"))
+      return "cheriot";
     if (Exts.count("e"))
       return "ilp32e";
     if (Exts.count("d"))