diff --git a/clang/CMakeLists.txt b/clang/CMakeLists.txt
index 9b52c58be41e7f7..1b88905da3b8597 100644
--- a/clang/CMakeLists.txt
+++ b/clang/CMakeLists.txt
@@ -300,6 +300,7 @@ configure_file(
   ${CMAKE_CURRENT_BINARY_DIR}/include/clang/Basic/Version.inc)
 
 # Add appropriate flags for GCC
+option(CLANG_ENABLE_PEDANTIC "Compile with pedantic enabled." ON)
 if (LLVM_COMPILER_IS_GCC_COMPATIBLE)
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fno-common -Woverloaded-virtual")
   if (NOT "${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang")
@@ -307,7 +308,7 @@ if (LLVM_COMPILER_IS_GCC_COMPATIBLE)
   endif ()
 
   # Enable -pedantic for Clang even if it's not enabled for LLVM.
-  if (NOT LLVM_ENABLE_PEDANTIC)
+  if (NOT LLVM_ENABLE_PEDANTIC AND CLANG_ENABLE_PEDANTIC)
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -pedantic -Wno-long-long")
   endif ()
 
diff --git a/clang/include/clang/AST/Expr.h b/clang/include/clang/AST/Expr.h
index b69c616b0090365..9303307fd6a8af5 100644
--- a/clang/include/clang/AST/Expr.h
+++ b/clang/include/clang/AST/Expr.h
@@ -4805,6 +4805,58 @@ class SourceLocExpr final : public Expr {
   friend class ASTStmtReader;
 };
 
+/// Represents a function call to __builtin_pp_embed().
+class PPEmbedExpr final : public Expr {
+  SourceLocation BuiltinLoc, RParenLoc;
+  DeclContext *ParentContext;
+  StringLiteral *Filename;
+  StringLiteral *BinaryData;
+
+public:
+  enum Action {
+    NotFound,
+    FoundOne,
+    Expanded,
+  };
+ 
+  PPEmbedExpr(const ASTContext &Ctx, QualType ResultTy, StringLiteral* Filename, StringLiteral* BinaryData,
+                SourceLocation BLoc, SourceLocation RParenLoc,
+                DeclContext *Context);
+
+  /// Build an empty call expression.
+  explicit PPEmbedExpr(EmptyShell Empty)
+      : Expr(SourceLocExprClass, Empty) {}
+
+  /// If the PPEmbedExpr has been resolved return the subexpression
+  /// representing the resolved value. Otherwise return null.
+  const DeclContext *getParentContext() const { return ParentContext; }
+  DeclContext *getParentContext() { return ParentContext; }
+
+  SourceLocation getLocation() const { return BuiltinLoc; }
+  SourceLocation getBeginLoc() const { return BuiltinLoc; }
+  SourceLocation getEndLoc() const { return RParenLoc; }
+
+  StringLiteral *getFilenameStringLiteral() const { return Filename; }
+  StringLiteral *getDataStringLiteral() const { return BinaryData; }
+
+  size_t getDataElementCount(ASTContext &Context) const;
+
+  child_range children() {
+    return child_range(child_iterator(), child_iterator());
+  }
+
+  const_child_range children() const {
+    return const_child_range(child_iterator(), child_iterator());
+  }
+
+  static bool classof(const Stmt *T) {
+    return T->getStmtClass() == PPEmbedExprClass;
+  }
+
+private:
+  friend class ASTStmtReader;
+};
+
 /// Describes an C or C++ initializer list.
 ///
 /// InitListExpr describes an initializer list, which can be used to
diff --git a/clang/include/clang/AST/RecursiveASTVisitor.h b/clang/include/clang/AST/RecursiveASTVisitor.h
index 3dd23eb38eeabfc..6b7211bb0a0d3f1 100644
--- a/clang/include/clang/AST/RecursiveASTVisitor.h
+++ b/clang/include/clang/AST/RecursiveASTVisitor.h
@@ -2809,6 +2809,7 @@ DEF_TRAVERSE_STMT(ShuffleVectorExpr, {})
 DEF_TRAVERSE_STMT(ConvertVectorExpr, {})
 DEF_TRAVERSE_STMT(StmtExpr, {})
 DEF_TRAVERSE_STMT(SourceLocExpr, {})
+DEF_TRAVERSE_STMT(PPEmbedExpr, {})
 
 DEF_TRAVERSE_STMT(UnresolvedLookupExpr, {
   TRY_TO(TraverseNestedNameSpecifierLoc(S->getQualifierLoc()));
diff --git a/clang/include/clang/Basic/Builtins.def b/clang/include/clang/Basic/Builtins.def
index 6ea8484606cfd5d..0dfc6456daf059a 100644
--- a/clang/include/clang/Basic/Builtins.def
+++ b/clang/include/clang/Basic/Builtins.def
@@ -1766,6 +1766,9 @@ BUILTIN(__builtin_ms_va_copy, "vc*&c*&", "n")
 // Arithmetic Fence: to prevent FP reordering and reassociation optimizations
 LANGBUILTIN(__arithmetic_fence, "v.", "tE", ALL_LANGUAGES)
 
+// preprocessor embed builtin
+LANGBUILTIN(__builtin_pp_embed, "v.", "tE", ALL_LANGUAGES)
+
 #undef BUILTIN
 #undef LIBBUILTIN
 #undef LANGBUILTIN
diff --git a/clang/include/clang/Basic/DiagnosticCommonKinds.td b/clang/include/clang/Basic/DiagnosticCommonKinds.td
index f2df283c74829f6..4df86e35eebde38 100644
--- a/clang/include/clang/Basic/DiagnosticCommonKinds.td
+++ b/clang/include/clang/Basic/DiagnosticCommonKinds.td
@@ -59,6 +59,9 @@ def err_expected_string_literal : Error<"expected string literal "
           "'external_source_symbol' attribute|"
           "as argument of '%1' attribute}0">;
 
+def err_builtin_pp_embed_invalid_argument : Error<
+  "invalid argument to '__builtin_pp_embed': %0">;
+
 def err_invalid_string_udl : Error<
   "string literal with user-defined suffix cannot be used here">;
 def err_invalid_character_udl : Error<
@@ -80,6 +83,9 @@ def err_expected : Error<"expected %0">;
 def err_expected_either : Error<"expected %0 or %1">;
 def err_expected_after : Error<"expected %1 after %0">;
 
+def err_builtin_pp_embed_invalid_location : Error<
+  "'__builtin_pp_embed' in invalid location: %0%select{|%2}1">;
+
 def err_param_redefinition : Error<"redefinition of parameter %0">;
 def warn_method_param_redefinition : Warning<"redefinition of method parameter %0">;
 def warn_method_param_declaration : Warning<"redeclaration of method parameter %0">,
diff --git a/clang/include/clang/Basic/DiagnosticGroups.td b/clang/include/clang/Basic/DiagnosticGroups.td
index 0b09c002191848a..7ebea56891d4654 100644
--- a/clang/include/clang/Basic/DiagnosticGroups.td
+++ b/clang/include/clang/Basic/DiagnosticGroups.td
@@ -708,6 +708,12 @@ def ReservedIdAsMacro : DiagGroup<"reserved-macro-identifier">;
 def ReservedIdAsMacroAlias : DiagGroup<"reserved-id-macro", [ReservedIdAsMacro]>;
 def RestrictExpansionMacro : DiagGroup<"restrict-expansion">;
 def FinalMacro : DiagGroup<"final-macro">;
+// Warnings about unknown preprocessor parameters (e.g. `#embed` and extensions)
+def UnsupportedDirective : DiagGroup<"unsupported-directive">;
+def UnknownDirectiveParameters : DiagGroup<"unknown-directive-parameters">;
+def IgnoredDirectiveParameters : DiagGroup<"ignored-directive-parameters">;
+def DirectiveParameters : DiagGroup<"directive-parameters",
+    [UnknownDirectiveParameters, IgnoredDirectiveParameters]>;
 
 // Just silence warnings about -Wstrict-aliasing for now.
 def : DiagGroup<"strict-aliasing=0">;
@@ -715,6 +721,7 @@ def : DiagGroup<"strict-aliasing=1">;
 def : DiagGroup<"strict-aliasing=2">;
 def : DiagGroup<"strict-aliasing">;
 
+
 // Just silence warnings about -Wstrict-overflow for now.
 def : DiagGroup<"strict-overflow=0">;
 def : DiagGroup<"strict-overflow=1">;
diff --git a/clang/include/clang/Basic/DiagnosticLexKinds.td b/clang/include/clang/Basic/DiagnosticLexKinds.td
index 940cca67368492f..4490f40806b0345 100644
--- a/clang/include/clang/Basic/DiagnosticLexKinds.td
+++ b/clang/include/clang/Basic/DiagnosticLexKinds.td
@@ -422,6 +422,22 @@ def warn_cxx23_compat_warning_directive : Warning<
 def warn_c23_compat_warning_directive : Warning<
   "#warning is incompatible with C standards before C23">,
   InGroup<CPre23Compat>, DefaultIgnore;
+def warn_c23_pp_embed : Warning<
+  "'__has_embed' is a C23 extension">,
+  InGroup<CPre23Compat>,
+  DefaultIgnore;
+def warn_c23_pp_has_embed : Warning<
+  "'__has_embed' is a C23 extension">,
+  InGroup<CPre23Compat>,
+  DefaultIgnore;
+def warn_cxx26_pp_embed : Warning<
+  "'__has_embed' is a C++26 extension">,
+  InGroup<CXXPre26Compat>,
+  DefaultIgnore;
+def warn_cxx26_pp_has_embed : Warning<
+  "'__has_embed' is a C++26 extension">,
+  InGroup<CXXPre26Compat>,
+  DefaultIgnore;
 
 def ext_pp_extra_tokens_at_eol : ExtWarn<
   "extra tokens at end of #%0 directive">, InGroup<ExtraTokens>;
@@ -483,7 +499,13 @@ def ext_pp_gnu_line_directive : Extension<
 def err_pp_invalid_directive : Error<
   "invalid preprocessing directive%select{|, did you mean '#%1'?}0">;
 def warn_pp_invalid_directive : Warning<
-  err_pp_invalid_directive.Summary>, InGroup<DiagGroup<"unknown-directives">>;
+  err_pp_invalid_directive.Summary>,
+  InGroup<UnsupportedDirective>;
+def warn_pp_unknown_parameter_ignored : Warning<
+  "unknown%select{ | embed}0 preprocessor parameter '%1' ignored">,
+  InGroup<UnknownDirectiveParameters>;
+def err_pp_unsupported_directive : Error<
+  "unsupported%select{ | embed}0 directive: %1">;
 def err_pp_directive_required : Error<
   "%0 must be used within a preprocessing directive">;
 def err_pp_file_not_found : Error<"'%0' file not found">, DefaultFatal;
diff --git a/clang/include/clang/Basic/FileManager.h b/clang/include/clang/Basic/FileManager.h
index 56cb093dd8c376f..c757f8775b425e9 100644
--- a/clang/include/clang/Basic/FileManager.h
+++ b/clang/include/clang/Basic/FileManager.h
@@ -276,11 +276,13 @@ class FileManager : public RefCountedBase<FileManager> {
   /// MemoryBuffer if successful, otherwise returning null.
   llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>>
   getBufferForFile(FileEntryRef Entry, bool isVolatile = false,
-                   bool RequiresNullTerminator = true);
+                   bool RequiresNullTerminator = true,
+                   std::optional<int64_t> MaybeLimit = std::nullopt);
   llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>>
   getBufferForFile(StringRef Filename, bool isVolatile = false,
-                   bool RequiresNullTerminator = true) {
-    return getBufferForFileImpl(Filename, /*FileSize=*/-1, isVolatile,
+                   bool RequiresNullTerminator = true,
+                   std::optional<int64_t> MaybeLimit = std::nullopt) {
+    return getBufferForFileImpl(Filename, /*FileSize=*/(MaybeLimit ? *MaybeLimit : -1), isVolatile,
                                 RequiresNullTerminator);
   }
 
diff --git a/clang/include/clang/Basic/StmtNodes.td b/clang/include/clang/Basic/StmtNodes.td
index cec301dfca2817b..e3be997dd1c86e0 100644
--- a/clang/include/clang/Basic/StmtNodes.td
+++ b/clang/include/clang/Basic/StmtNodes.td
@@ -203,6 +203,7 @@ def OpaqueValueExpr : StmtNode<Expr>;
 def TypoExpr : StmtNode<Expr>;
 def RecoveryExpr : StmtNode<Expr>;
 def BuiltinBitCastExpr : StmtNode<ExplicitCastExpr>;
+def PPEmbedExpr : StmtNode<Expr>;
 
 // Microsoft Extensions.
 def MSPropertyRefExpr : StmtNode<Expr>;
diff --git a/clang/include/clang/Basic/TokenKinds.def b/clang/include/clang/Basic/TokenKinds.def
index 94db56a9fd5d78c..167bd614efe7bd9 100644
--- a/clang/include/clang/Basic/TokenKinds.def
+++ b/clang/include/clang/Basic/TokenKinds.def
@@ -126,6 +126,9 @@ PPKEYWORD(error)
 // C99 6.10.6 - Pragma Directive.
 PPKEYWORD(pragma)
 
+// C23 & C++26 #embed
+PPKEYWORD(embed)
+
 // GNU Extensions.
 PPKEYWORD(import)
 PPKEYWORD(include_next)
@@ -751,6 +754,7 @@ ALIAS("__char32_t"   , char32_t          , KEYCXX)
 KEYWORD(__builtin_bit_cast               , KEYALL)
 KEYWORD(__builtin_available              , KEYALL)
 KEYWORD(__builtin_sycl_unique_stable_name, KEYSYCL)
+KEYWORD(__builtin_pp_embed               , KEYALL)
 
 // Keywords defined by Attr.td.
 #ifndef KEYWORD_ATTRIBUTE
@@ -986,6 +990,7 @@ ANNOTATION(repl_input_end)
 #undef CXX11_KEYWORD
 #undef KEYWORD
 #undef PUNCTUATOR
+#undef BUILTINOK
 #undef TOK
 #undef C99_KEYWORD
 #undef C23_KEYWORD
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index 5415b18d3f406df..bfc4b15d5411cde 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -114,6 +114,11 @@ def IncludePath_Group : OptionGroup<"<I/i group>">, Group<Preprocessor_Group>,
                         DocBrief<[{
 Flags controlling how ``#include``\s are resolved to files.}]>;
 
+def EmbedPath_Group : OptionGroup<"<Embed group>">, Group<Preprocessor_Group>,
+                        DocName<"Embed path management">,
+                        DocBrief<[{
+Flags controlling how ``#embed``\s and similar are resolved to files.}]>;
+
 def I_Group : OptionGroup<"<I group>">, Group<IncludePath_Group>, DocFlatten;
 def i_Group : OptionGroup<"<i group>">, Group<IncludePath_Group>, DocFlatten;
 def clang_i_Group : OptionGroup<"<clang i group>">, Group<i_Group>, DocFlatten;
@@ -816,6 +821,14 @@ will be ignored}]>;
 def L : JoinedOrSeparate<["-"], "L">, Flags<[RenderJoined]>, Group<Link_Group>,
     Visibility<[ClangOption, FlangOption]>,
     MetaVarName<"<dir>">, HelpText<"Add directory to library search path">;
+def embed_dir : JoinedOrSeparate<["-"], "embed-dir">,
+    Flags<[RenderJoined]>, Group<EmbedPath_Group>,
+    Visibility<[ClangOption, CC1Option, CC1AsOption, FlangOption, FC1Option]>,
+    MetaVarName<"<dir>">, HelpText<"Add directory to embed search path">;
+def embed_dir_EQ : JoinedOrSeparate<["-"], "embed-dir=">,
+    Flags<[RenderJoined]>, Group<EmbedPath_Group>,
+    Visibility<[ClangOption, CC1Option, CC1AsOption, FlangOption, FC1Option]>,
+    MetaVarName<"<dir>">, HelpText<"Add directory to embed search path">;
 def MD : Flag<["-"], "MD">, Group<M_Group>,
     HelpText<"Write a depfile containing user and system headers">;
 def MMD : Flag<["-"], "MMD">, Group<M_Group>,
@@ -1353,6 +1366,9 @@ def dD : Flag<["-"], "dD">, Group<d_Group>, Visibility<[ClangOption, CC1Option]>
 def dI : Flag<["-"], "dI">, Group<d_Group>, Visibility<[ClangOption, CC1Option]>,
   HelpText<"Print include directives in -E mode in addition to normal output">,
   MarshallingInfoFlag<PreprocessorOutputOpts<"ShowIncludeDirectives">>;
+def dE : Flag<["-"], "dE">, Group<d_Group>, Visibility<[ClangOption, CC1Option]>,
+  HelpText<"Print embed directives in -E mode in addition to normal output">,
+  MarshallingInfoFlag<PreprocessorOutputOpts<"ShowEmbedDirectives">>;
 def dM : Flag<["-"], "dM">, Group<d_Group>, Visibility<[ClangOption, CC1Option]>,
   HelpText<"Print macro definitions in -E mode instead of normal output">;
 def dead__strip : Flag<["-"], "dead_strip">;
diff --git a/clang/include/clang/Frontend/PreprocessorOutputOptions.h b/clang/include/clang/Frontend/PreprocessorOutputOptions.h
index db2ec9f2ae20698..3e36db3f8ce46ea 100644
--- a/clang/include/clang/Frontend/PreprocessorOutputOptions.h
+++ b/clang/include/clang/Frontend/PreprocessorOutputOptions.h
@@ -22,6 +22,7 @@ class PreprocessorOutputOptions {
   unsigned ShowMacroComments : 1;  ///< Show comments, even in macros.
   unsigned ShowMacros : 1;         ///< Print macro definitions.
   unsigned ShowIncludeDirectives : 1;  ///< Print includes, imports etc. within preprocessed output.
+  unsigned ShowEmbedDirectives : 1;  ///< Print embeds, etc. within preprocessed output.
   unsigned RewriteIncludes : 1;    ///< Preprocess include directives only.
   unsigned RewriteImports  : 1;    ///< Include contents of transitively-imported modules.
   unsigned MinimizeWhitespace : 1; ///< Ignore whitespace from input.
@@ -37,6 +38,7 @@ class PreprocessorOutputOptions {
     ShowMacroComments = 0;
     ShowMacros = 0;
     ShowIncludeDirectives = 0;
+    ShowEmbedDirectives = 0;
     RewriteIncludes = 0;
     RewriteImports = 0;
     MinimizeWhitespace = 0;
diff --git a/clang/include/clang/Lex/PPCallbacks.h b/clang/include/clang/Lex/PPCallbacks.h
index 94f96cf9c512541..7028c81dbc84aac 100644
--- a/clang/include/clang/Lex/PPCallbacks.h
+++ b/clang/include/clang/Lex/PPCallbacks.h
@@ -22,11 +22,11 @@
 #include "llvm/ADT/StringRef.h"
 
 namespace clang {
-  class Token;
-  class IdentifierInfo;
-  class MacroDefinition;
-  class MacroDirective;
-  class MacroArgs;
+class Token;
+class IdentifierInfo;
+class MacroDefinition;
+class MacroDirective;
+class MacroArgs;
 
 /// This interface provides a way to observe the actions of the
 /// preprocessor as it does its thing.
@@ -36,9 +36,7 @@ class PPCallbacks {
 public:
   virtual ~PPCallbacks();
 
-  enum FileChangeReason {
-    EnterFile, ExitFile, SystemHeaderPragma, RenameFile
-  };
+  enum FileChangeReason { EnterFile, ExitFile, SystemHeaderPragma, RenameFile };
 
   /// Callback invoked whenever a source file is entered or exited.
   ///
@@ -47,8 +45,7 @@ class PPCallbacks {
   /// the file before the new one entered for \p Reason EnterFile.
   virtual void FileChanged(SourceLocation Loc, FileChangeReason Reason,
                            SrcMgr::CharacteristicKind FileType,
-                           FileID PrevFID = FileID()) {
-  }
+                           FileID PrevFID = FileID()) {}
 
   enum class LexedFileChangeReason { EnterFile, ExitFile };
 
@@ -83,6 +80,47 @@ class PPCallbacks {
                            const Token &FilenameTok,
                            SrcMgr::CharacteristicKind FileType) {}
 
+  /// Callback invoked whenever the preprocessor cannot find a file for an
+  /// embed directive.
+  ///
+  /// \param FileName The name of the file being included, as written in the
+  /// source code.
+  ///
+  /// \returns true to indicate that the preprocessor should skip this file
+  /// and not issue any diagnostic.
+  virtual bool EmbedFileNotFound(StringRef FileName) { return false; }
+
+  /// Callback invoked whenever an embed directive has been processed,
+  /// regardless of whether the embed will actually find a file.
+  ///
+  /// \param HashLoc The location of the '#' that starts the embed directive.
+  ///
+  /// \param FileName The name of the file being included, as written in the
+  /// source code.
+  ///
+  /// \param IsAngled Whether the file name was enclosed in angle brackets;
+  /// otherwise, it was enclosed in quotes.
+  ///
+  /// \param FilenameRange The character range of the quotes or angle brackets
+  /// for the written file name.
+  ///
+  /// \param ParametersRange The character range of the embed parameters. An
+  /// empty range if there were no parameters.
+  ///
+  /// \param File The actual file that may be included by this embed directive.
+  ///
+  /// \param SearchPath Contains the search path which was used to find the file
+  /// in the file system. If the file was found via an absolute path,
+  /// SearchPath will be empty.
+  ///
+  /// \param RelativePath The path relative to SearchPath, at which the resource
+  /// file was found. This is equal to FileName.
+  virtual void EmbedDirective(SourceLocation HashLoc, StringRef FileName,
+                              bool IsAngled, CharSourceRange FilenameRange,
+                              CharSourceRange ParametersRange,
+                              OptionalFileEntryRef File, StringRef SearchPath,
+                              StringRef RelativePath) {}
+
   /// Callback invoked whenever the preprocessor cannot find a file for an
   /// inclusion directive.
   ///
@@ -151,7 +189,7 @@ class PPCallbacks {
   /// \param ForPragma If entering from pragma directive.
   ///
   virtual void EnteredSubmodule(Module *M, SourceLocation ImportLoc,
-                                bool ForPragma) { }
+                                bool ForPragma) {}
 
   /// Callback invoked whenever a submodule was left.
   ///
@@ -162,7 +200,7 @@ class PPCallbacks {
   /// \param ForPragma If entering from pragma directive.
   ///
   virtual void LeftSubmodule(Module *M, SourceLocation ImportLoc,
-                             bool ForPragma) { }
+                             bool ForPragma) {}
 
   /// Callback invoked whenever there was an explicit module-import
   /// syntax.
@@ -174,49 +212,40 @@ class PPCallbacks {
   ///
   /// \param Imported The imported module; can be null if importing failed.
   ///
-  virtual void moduleImport(SourceLocation ImportLoc,
-                            ModuleIdPath Path,
-                            const Module *Imported) {
-  }
+  virtual void moduleImport(SourceLocation ImportLoc, ModuleIdPath Path,
+                            const Module *Imported) {}
 
   /// Callback invoked when the end of the main file is reached.
   ///
   /// No subsequent callbacks will be made.
-  virtual void EndOfMainFile() {
-  }
+  virtual void EndOfMainFile() {}
 
   /// Callback invoked when a \#ident or \#sccs directive is read.
   /// \param Loc The location of the directive.
   /// \param str The text of the directive.
   ///
-  virtual void Ident(SourceLocation Loc, StringRef str) {
-  }
+  virtual void Ident(SourceLocation Loc, StringRef str) {}
 
   /// Callback invoked when start reading any pragma directive.
   virtual void PragmaDirective(SourceLocation Loc,
-                               PragmaIntroducerKind Introducer) {
-  }
+                               PragmaIntroducerKind Introducer) {}
 
   /// Callback invoked when a \#p...
[truncated]