[Downstream change][Multilib] Extend the Multilib system to support an IncludeDirs field. (#447)

Downstream issue:#446.

This patch extends the Multilib yaml format to allow specifying an
IncludeDirs for the header path/s per multilib variant. The goal is to
enable fine-grained control over header search paths for each multilib
variant. This feature is especially useful in setups where header paths
deviate from the default bare-metal assumptions. For example, when
headers are shared across target triples, it becomes necessary to
organise them under target-triple-specific directories to ensure correct
resolution.

This is already in upstream review
llvm/llvm-project#146651.
Since the review is pending, a downstream patch is made to enable
IncludeDirs support in multilib.yaml

Author: simpal01

clang/include/clang/Driver/Multilib.h

@@ -35,12 +35,18 @@ class Driver;
 class Multilib {
 public:
   using flags_list = std::vector<std::string>;
+  // Downstream issue: #446 (Extend the Multilib system to support an
+  // IncludeDirs field)
+  using includedirs_list = std::vector<std::string>;
 
 private:
   std::string GCCSuffix;
   std::string OSSuffix;
   std::string IncludeSuffix;
   flags_list Flags;
+  // Downstream issue: #446 (Extend the Multilib system to support an
+  // IncludeDirs field)
+  includedirs_list IncludeDirs;
 
   // Optionally, a multilib can be assigned a string tag indicating that it's
   // part of a group of mutually exclusive possibilities. If two or more
@@ -62,6 +68,9 @@ class Multilib {
   /// This is enforced with an assert in the constructor.
   Multilib(StringRef GCCSuffix = {}, StringRef OSSuffix = {},
            StringRef IncludeSuffix = {}, const flags_list &Flags = flags_list(),
+           // Downstream issue: #446 (Extend the Multilib system to support an
+           // IncludeDirs field)
+           const includedirs_list &IncludeDirs = includedirs_list(),
            StringRef ExclusiveGroup = {},
            std::optional<StringRef> Error = std::nullopt);
 
@@ -81,6 +90,12 @@ class Multilib {
   /// All elements begin with either '-' or '!'
   const flags_list &flags() const { return Flags; }
 
+  // Downstream issue: #446 (Extend the Multilib system to support an
+  // IncludeDirs field)
+  /// Get the include directories specified in multilib.yaml under the
+  /// 'IncludeDirs' field
+  const includedirs_list &includeDirs() const { return IncludeDirs; }
+
   /// Get the exclusive group label.
   const std::string &exclusiveGroup() const { return ExclusiveGroup; }
 

clang/lib/Driver/Multilib.cpp

@@ -29,9 +29,15 @@ using namespace llvm::sys;
 
 Multilib::Multilib(StringRef GCCSuffix, StringRef OSSuffix,
                    StringRef IncludeSuffix, const flags_list &Flags,
+                   // Downstream issue: #446 (Extend the Multilib system to
+                   // support an IncludeDirs field)
+                   const includedirs_list &IncludeDirs,
                    StringRef ExclusiveGroup, std::optional<StringRef> Error)
     : GCCSuffix(GCCSuffix), OSSuffix(OSSuffix), IncludeSuffix(IncludeSuffix),
-      Flags(Flags), ExclusiveGroup(ExclusiveGroup), Error(Error) {
+      Flags(Flags),
+      // Downstream issue: #446 (Extend the Multilib system to support an
+      // IncludeDirs field)
+      IncludeDirs(IncludeDirs), ExclusiveGroup(ExclusiveGroup), Error(Error) {
   assert(GCCSuffix.empty() ||
          (StringRef(GCCSuffix).front() == '/' && GCCSuffix.size() > 1));
   assert(OSSuffix.empty() ||
@@ -299,6 +305,9 @@ struct MultilibSerialization {
   std::string Dir;        // if this record successfully selects a library dir
   std::string Error;      // if this record reports a fatal error message
   std::vector<std::string> Flags;
+  // Downstream issue: #446 (Extend the Multilib system to support an
+  // IncludeDirs field)
+  std::vector<std::string> IncludeDirs;
   std::string Group;
 };
 
@@ -350,6 +359,9 @@ template <> struct llvm::yaml::MappingTraits<MultilibSerialization> {
     io.mapOptional("Dir", V.Dir);
     io.mapOptional("Error", V.Error);
     io.mapRequired("Flags", V.Flags);
+    // Downstream issue: #446 (Extend the Multilib system to support an
+    // IncludeDirs field)
+    io.mapOptional("IncludeDirs", V.IncludeDirs);
     io.mapOptional("Group", V.Group);
   }
   static std::string validate(IO &io, MultilibSerialization &V) {
@@ -359,6 +371,12 @@ template <> struct llvm::yaml::MappingTraits<MultilibSerialization> {
       return "the 'Dir' and 'Error' keys may not both be specified";
     if (StringRef(V.Dir).starts_with("/"))
       return "paths must be relative but \"" + V.Dir + "\" starts with \"/\"";
+    // Downstream issue: #446 (Extend the Multilib system to support an
+    // IncludeDirs field)
+    for (const auto &Path : V.IncludeDirs) {
+      if (StringRef(Path).starts_with("/"))
+        return "paths must be relative but \"" + Path + "\" starts with \"/\"";
+    }
     return std::string{};
   }
 };
@@ -489,7 +507,10 @@ MultilibSet::parseYaml(llvm::MemoryBufferRef Input,
   Multilibs.reserve(MS.Multilibs.size());
   for (const auto &M : MS.Multilibs) {
     if (!M.Error.empty()) {
-      Multilibs.emplace_back("", "", "", M.Flags, M.Group, M.Error);
+      // Downstream issue: #446 (Extend the Multilib system to support an
+      // IncludeDirs field)
+      Multilibs.emplace_back("", "", "", M.Flags, M.IncludeDirs, M.Group,
+                             M.Error);
     } else {
       std::string Dir;
       if (M.Dir != ".")
@@ -498,7 +519,9 @@ MultilibSet::parseYaml(llvm::MemoryBufferRef Input,
       // Multilib constructor. If we later support more than one type of group,
       // we'll have to look up the group name in MS.Groups, check its type, and
       // decide what to do here.
-      Multilibs.emplace_back(Dir, Dir, Dir, M.Flags, M.Group);
+      // Downstream issue: #446 (Extend the Multilib system to support an
+      // IncludeDirs field)
+      Multilibs.emplace_back(Dir, Dir, Dir, M.Flags, M.IncludeDirs, M.Group);
     }
   }
 

clang/lib/Driver/ToolChains/BareMetal.cpp

@@ -427,10 +427,22 @@ void BareMetal::AddClangSystemIncludeArgs(const ArgList &DriverArgs,
   const SmallString<128> SysRootDir(computeSysRoot());
   if (!SysRootDir.empty()) {
     for (const Multilib &M : getOrderedMultilibs()) {
-      SmallString<128> Dir(SysRootDir);
-      llvm::sys::path::append(Dir, M.includeSuffix());
-      llvm::sys::path::append(Dir, "include");
-      addSystemInclude(DriverArgs, CC1Args, Dir.str());
+      // Downstream issue: #446 (Extend the Multilib system to support an
+      // IncludeDirs field)
+      if (!M.includeDirs().empty()) {
+        // Add include directories specified in multilib.yaml under the
+        // 'IncludeDirs' field
+        for (const std::string &Path : M.includeDirs()) {
+          SmallString<128> Dir(SysRoot);
+          llvm::sys::path::append(Dir, Path);
+          addSystemInclude(DriverArgs, CC1Args, Dir.str());
+        }
+      } else {
+        SmallString<128> Dir(SysRootDir);
+        llvm::sys::path::append(Dir, M.includeSuffix());
+        llvm::sys::path::append(Dir, "include");
+        addSystemInclude(DriverArgs, CC1Args, Dir.str());
+      }
     }
   }
 }
@@ -511,6 +523,18 @@ void BareMetal::AddClangCXXStdlibIncludeArgs(const ArgList &DriverArgs,
         addSystemInclude(DriverArgs, CC1Args, TargetDir.str());
         break;
       }
+      // Downstream issue: #446 (Extend the Multilib system to support an
+      // IncludeDirs field)
+      if (!M.includeDirs().empty()) {
+        // Add include directories specified in multilib.yaml under the
+        // 'IncludeDirs' field
+        for (const std::string &Path : M.includeDirs()) {
+          Dir = SysRoot;
+          llvm::sys::path::append(Dir, Path, "c++", "v1");
+          addSystemInclude(DriverArgs, CC1Args, Dir.str());
+        }
+        break;
+      }
       // Add generic path if nothing else succeeded so far.
       llvm::sys::path::append(Dir, "include", "c++", "v1");
       addSystemInclude(DriverArgs, CC1Args, Dir.str());

clang/test/Driver/baremetal-multilib-includedirs-error.yaml

@@ -0,0 +1,30 @@
+# Downstream issue: #446 (Extend the Multilib system to support an IncludeDirs field)
+# REQUIRES: shell
+# UNSUPPORTED: system-windows
+
+# This test demonstrates the new "IncludeDirs" field.
+# This field allows specifying include directories through
+# multilib.yaml configuration using relative paths.
+# Absolute paths should be rejected by the driver
+# with an appropriate diagnostic message.
+#
+# This test verifies that passing an absolute path
+# (/include) to IncludeDirs triggers the expected
+# error.
+
+# RUN: not %clang --target=aarch64-none-elf --multi-lib-config=%s %s -o /dev/null 2>&1 \
+# RUN: | FileCheck %s --check-prefix=CHECK-ERROR
+# CHECK-ERROR: error: paths must be relative but "/include" starts with "/"
+
+---
+MultilibVersion: 1.0
+Variants:
+- Dir: aarch64-none-elf/aarch64a_exn_rtti_unaligned
+  Flags:
+  - --target=aarch64-unknown-none-elf
+  - -munaligned-access
+  IncludeDirs:
+  - /include
+  - aarch64-none-elf/include
+
+...

clang/test/Driver/baremetal-multilib-includedirs.yaml

@@ -0,0 +1,33 @@
+# Downstream issue: #446 (Extend the Multilib system to support an IncludeDirs field)
+# REQUIRES: shell
+# UNSUPPORTED: system-windows
+
+# This test demonstrates the new "IncludeDirs" field.
+# This field allows specifying include directories through
+# multilib.yaml configuration. When this field is present
+# it is appended to the sysroot during header path
+# resolution ignoring the default bare-metal assumptions.
+
+# RUN: %clang --multi-lib-config=%s -no-canonical-prefixes -x c++ %s -### -o %t.out 2>&1 \
+# RUN:     --target=thumbv7m-none-eabi -mfloat-abi=soft --sysroot= \
+# RUN:   | FileCheck %s
+# CHECK:      "-cc1" "-triple" "thumbv7m-unknown-none-eabi"
+# CHECK-SAME: "-internal-isystem" "[[SYSROOT:[^"]*]]/bin/../lib/clang-runtimes/include/c++/v1"
+# CHECK-SAME: "-internal-isystem" "[[SYSROOT]]/bin/../lib/clang-runtimes/include-libunwind/c++/v1"
+# CHECK-SAME: "-internal-isystem" "[[SYSROOT]]/bin/../lib/clang-runtimes/soft/include/c++/v1"
+# CHECK-SAME: "-internal-isystem" "[[SYSROOT]]/bin/../lib/clang-runtimes/include"
+# CHECK-SAME: "-internal-isystem" "[[SYSROOT]]/bin/../lib/clang-runtimes/include-libunwind"
+# CHECK-SAME: "-internal-isystem" "[[SYSROOT]]/bin/../lib/clang-runtimes/soft/include"
+
+---
+MultilibVersion: 1.0
+Variants:
+- Dir: soft
+  Flags:
+    - -mfloat-abi=soft
+  IncludeDirs:
+    - include
+    - include-libunwind
+    - soft/include
+
+...