diff --git a/BaseTools/Conf/build_rule.template b/BaseTools/Conf/build_rule.template
index db06d3a6b45a..fb8a20f25acc 100755
--- a/BaseTools/Conf/build_rule.template
+++ b/BaseTools/Conf/build_rule.template
@@ -260,7 +260,7 @@
     <OutputFile>
         $(OUTPUT_DIR)(+)$(MODULE_NAME).lib
 
-    <Command.MSFT, Command.INTEL>
+    <Command.MSFT, Command.INTEL, Command.CLANGPE>
         "$(SLINK)" $(SLINK_FLAGS) /OUT:${dst} @$(OBJECT_FILES_LIST)
 
     <Command.GCC>
@@ -291,6 +291,9 @@
         "$(DLINK)" /OUT:${dst} $(DLINK_FLAGS) $(DLINK2_FLAGS) $(DLINK_SPATH) @$(STATIC_LIBRARY_FILES_LIST)
         "$(DLINK)" /OUT:${dst} $(DLINK_FLAGS) $(DLINK_SPATH) @$(STATIC_LIBRARY_FILES_LIST)
 
+    <Command.CLANGPE>
+        "$(DLINK)" /OUT:${dst} $(DLINK_FLAGS) $(DLINK_SPATH) @$(STATIC_LIBRARY_FILES_LIST) $(DLINK2_FLAGS)
+
     <Command.GCC>
         "$(DLINK)" -o ${dst} $(DLINK_FLAGS) -Wl,--start-group,@$(STATIC_LIBRARY_FILES_LIST),--end-group $(CC_FLAGS) $(DLINK2_FLAGS)
         "$(OBJCOPY)" $(OBJCOPY_FLAGS) ${dst}
@@ -331,7 +334,7 @@
     <OutputFile>
         $(DEBUG_DIR)(+)$(MODULE_NAME)
 
-    <Command.MSFT, Command.INTEL>
+    <Command.MSFT, Command.INTEL, Command.CLANGPE>
         "$(DLINK)" $(DLINK_FLAGS) $(DLINK_SPATH) @$(STATIC_LIBRARY_FILES_LIST)
 
     <Command.GCC>
@@ -355,7 +358,7 @@
     <OutputFile>
         $(OUTPUT_DIR)(+)$(MODULE_NAME).efi
 
-    <Command.MSFT, Command.INTEL, Command.RVCT>
+    <Command.MSFT, Command.INTEL, Command.RVCT, Command.CLANGPE>
         "$(GENFW)" -e $(MODULE_TYPE) -o ${dst} ${src} $(GENFW_FLAGS)
         $(CP) ${dst} $(DEBUG_DIR)
         $(CP) ${dst} $(BIN_DIR)(+)$(MODULE_NAME_GUID).efi
@@ -460,9 +463,14 @@
 
     <Command.GCC>
         "$(ASLCC)" -c -o $(OUTPUT_DIR)(+)${s_dir}(+)${s_base}.obj $(CC_FLAGS) $(ASLCC_FLAGS) $(INC) ${src}
-        "$(ASLDLINK)" -o $(OUTPUT_DIR)(+)${s_dir}(+)${s_base}.dll $(ASLDLINK_FLAGS) $(OUTPUT_DIR)(+)${s_dir}(+)${s_base}.obj
+        "$(ASLDLINK)" -o $(OUTPUT_DIR)(+)${s_dir}(+)${s_base}.dll $(ASLDLINK_FLAGS) $(OUTPUT_DIR)(+)${s_dir}(+)${s_base}.obj $(CC_FLAGS) $(ASLCC_FLAGS)
         "$(GENFW)" -o ${dst} -c $(OUTPUT_DIR)(+)${s_dir}(+)${s_base}.dll $(GENFW_FLAGS)
-        
+
+    <Command.CLANGPE>
+        "$(ASLCC)" -c -o $(OUTPUT_DIR)(+)${s_dir}(+)${s_base}.obj $(CC_FLAGS) $(ASLCC_FLAGS) $(INC) ${src}
+        "$(ASLDLINK)" /OUT:$(OUTPUT_DIR)(+)${s_dir}(+)${s_base}.dll $(ASLDLINK_FLAGS) $(OUTPUT_DIR)(+)${s_dir}(+)${s_base}.obj
+        "$(GENFW)" -o ${dst} -c $(OUTPUT_DIR)(+)${s_dir}(+)${s_base}.dll $(GENFW_FLAGS)
+
     <Command.XCODE>        
         "$(ASLCC)" -o $(OUTPUT_DIR)(+)${s_dir}(+)${s_base}.obj  $(ASLCC_FLAGS) $(INC) ${src}
         "$(ASLDLINK)" -o $(OUTPUT_DIR)(+)${s_dir}(+)${s_base}.dll $(ASLDLINK_FLAGS) $(OUTPUT_DIR)(+)${s_dir}(+)${s_base}.obj
@@ -628,7 +636,7 @@
     <OutputFile.XCODE, OutputFile.RVCT>
         $(OUTPUT_DIR)(+)$(MODULE_NAME)hii.rc
 
-    <Command.MSFT, Command.INTEL>
+    <Command.MSFT, Command.INTEL, Command.CLANGPE>
         "$(GENFW)" -o $(OUTPUT_DIR)(+)$(MODULE_NAME)hii.rc -g $(MODULE_GUID) --hiipackage $(HII_BINARY_PACKAGES) $(GENFW_FLAGS)
         "$(RC)" /Fo${dst} $(OUTPUT_DIR)(+)$(MODULE_NAME)hii.rc
 
@@ -636,7 +644,7 @@
         "$(GENFW)" -o $(OUTPUT_DIR)(+)$(MODULE_NAME)hii.rc -g $(MODULE_GUID) --hiibinpackage $(HII_BINARY_PACKAGES) $(GENFW_FLAGS)
         "$(RC)" $(RC_FLAGS) $(OUTPUT_DIR)(+)$(MODULE_NAME)hii.rc ${dst}
         
-    <Command.XCODE, Command.RVCT>
+    <Command.XCODE, Command.RVCT, Command.CLANGGCC>
         GenFw -o $(OUTPUT_DIR)(+)$(MODULE_NAME)hii.rc -g $(MODULE_GUID) --hiibinpackage $(HII_BINARY_PACKAGES)
         
         
diff --git a/BaseTools/Conf/tools_def.template b/BaseTools/Conf/tools_def.template
index 8f0e6cb6c2cb..e3f3c6bdcfe7 100755
--- a/BaseTools/Conf/tools_def.template
+++ b/BaseTools/Conf/tools_def.template
@@ -249,6 +249,15 @@ DEFINE DTC_BIN                 = ENV(DTC_PREFIX)dtc
 #                             Required to build platforms or ACPI tables:
 #                               Intel(r) ACPI Compiler from
 #                               https://acpica.org/downloads
+#   CLANG9PE  -Linux, Windows, Mac-  Requires:
+#                             Clang 9 or above from http://releases.llvm.org/
+#                        Optional:
+#                             Required to compile nasm source:
+#                               nasm compiler from
+#                               NASM -- http://www.nasm.us/
+#                             Required to build platforms or ACPI tables:
+#                               Intel(r) ACPI Compiler from
+#                               https://acpica.org/downloads
 #   VS2008x86   -win64-  Requires:
 #                             Microsoft Visual Studio 2008 (x86)
 #                             Microsoft Windows Server 2003 Driver Development Kit (Microsoft WINDDK) version 3790.1830
@@ -331,8 +340,8 @@ DEFINE DTC_BIN                 = ENV(DTC_PREFIX)dtc
 # *_*_EBC_SLINK_PATH                 = C:\Program Files\Intel\EBC\Bin\link.exe
 #
 # *_*_EBC_SLINK_FLAGS                = /lib /NOLOGO /MACHINE:EBC
-# *_*_EBC_PP_FLAGS                   = /nologo /E /TC /FI$(DEST_DIR_DEBUG)/AutoGen.h
-# *_*_EBC_CC_FLAGS                   = /nologo /FAcs /c /W3 /WX /FI$(DEST_DIR_DEBUG)/AutoGen.h
+# *_*_EBC_PP_FLAGS                   = /nologo /E /TC /FIAutoGen.h
+# *_*_EBC_CC_FLAGS                   = /nologo /FAcs /c /W3 /WX /FIAutoGen.h
 # *_*_EBC_DLINK_FLAGS                = "C:\Program Files\Intel\EBC\Lib\EbcLib.lib" /NOLOGO /MACHINE:EBC /OPT:REF /NODEFAULTLIB /ENTRY:$(IMAGE_ENTRY_POINT) /SUBSYSTEM:EFI_BOOT_SERVICE_DRIVER /ALIGN:32 /DRIVER
 #
 ####################################################################################
@@ -1724,13 +1733,13 @@ DEFINE GCC_IA32_X64_ASLDLINK_FLAGS = DEF(GCC_IA32_X64_DLINK_COMMON) --entry _Ref
 DEFINE GCC_ARM_ASLDLINK_FLAGS      = DEF(GCC_ARM_DLINK_FLAGS) -Wl,--entry,ReferenceAcpiTable -u $(IMAGE_ENTRY_POINT) DEF(GCC_ARM_AARCH64_ASLDLINK_FLAGS)
 DEFINE GCC_AARCH64_ASLDLINK_FLAGS  = DEF(GCC_AARCH64_DLINK_FLAGS) -Wl,--entry,ReferenceAcpiTable -u $(IMAGE_ENTRY_POINT) DEF(GCC_ARM_AARCH64_ASLDLINK_FLAGS)
 DEFINE GCC_IA32_X64_DLINK_FLAGS    = DEF(GCC_IA32_X64_DLINK_COMMON) --entry _$(IMAGE_ENTRY_POINT) --file-alignment 0x20 --section-alignment 0x20 -Map $(DEST_DIR_DEBUG)/$(BASE_NAME).map
-DEFINE GCC_ASM_FLAGS               = -c -x assembler -imacros $(DEST_DIR_DEBUG)/AutoGen.h
-DEFINE GCC_PP_FLAGS                = -E -x assembler-with-cpp -include $(DEST_DIR_DEBUG)/AutoGen.h
-DEFINE GCC_VFRPP_FLAGS             = -x c -E -P -DVFRCOMPILE --include $(DEST_DIR_DEBUG)/$(MODULE_NAME)StrDefs.h
+DEFINE GCC_ASM_FLAGS               = -c -x assembler -imacros AutoGen.h
+DEFINE GCC_PP_FLAGS                = -E -x assembler-with-cpp -include AutoGen.h
+DEFINE GCC_VFRPP_FLAGS             = -x c -E -P -DVFRCOMPILE --include $(MODULE_NAME)StrDefs.h
 DEFINE GCC_ASLPP_FLAGS             = -x c -E -include AutoGen.h
 DEFINE GCC_ASLCC_FLAGS             = -x c
 DEFINE GCC_WINDRES_FLAGS           = -J rc -O coff
-DEFINE GCC_DTCPP_FLAGS             = -E -x assembler-with-cpp -imacros $(DEST_DIR_DEBUG)/AutoGen.h -nostdinc -undef
+DEFINE GCC_DTCPP_FLAGS             = -E -x assembler-with-cpp -imacros AutoGen.h -nostdinc -undef
 DEFINE GCC_IA32_RC_FLAGS           = -I binary -O elf32-i386          -B i386    --rename-section .data=.hii
 DEFINE GCC_X64_RC_FLAGS            = -I binary -O elf64-x86-64        -B i386    --rename-section .data=.hii
 DEFINE GCC_ARM_RC_FLAGS            = -I binary -O elf32-littlearm     -B arm     --rename-section .data=.hii
@@ -2516,6 +2525,99 @@ DEFINE CLANG38_AARCH64_DLINK_FLAGS  = DEF(CLANG38_AARCH64_TARGET) DEF(GCC_AARCH6
 RELEASE_CLANG38_AARCH64_CC_FLAGS    = DEF(CLANG38_AARCH64_CC_FLAGS) $(ARCHCC_FLAGS) $(PLATFORM_FLAGS) -flto -O3
 RELEASE_CLANG38_AARCH64_DLINK_FLAGS = DEF(CLANG38_AARCH64_DLINK_FLAGS) -flto -Wl,-O3 -L$(WORKSPACE)/ArmPkg/Library/GccLto -llto-aarch64 -Wl,-plugin-opt=-pass-through=-llto-aarch64
 
+####################################################################################
+#
+# Clang9 PE - This configuration is used to compile under Windows/Linux/Mac to produce
+#  PE/COFF binaries using LLVM/Clang/LLD with Link Time Optimization enabled
+#
+####################################################################################
+*_CLANG9PE_*_*_FAMILY                = GCC
+*_CLANG9PE_*_*_BUILDRULEFAMILY       = CLANGPE
+*_CLANG9PE_*_MAKE_PATH               = ENV(CLANG_HOST_BIN)make
+*_CLANG9PE_*_*_DLL                   = ENV(CLANG9PE_DLL)
+*_CLANG9PE_*_ASL_PATH                = DEF(UNIX_IASL_BIN)
+
+*_CLANG9PE_*_APP_FLAGS               =
+*_CLANG9PE_*_ASL_FLAGS               = DEF(DEFAULT_WIN_ASL_FLAGS)
+*_CLANG9PE_*_ASL_OUTFLAGS            = DEF(DEFAULT_WIN_ASL_OUTFLAGS)
+*_CLANG9PE_*_ASLDLINK_FLAGS          = DEF(MSFT_ASLDLINK_FLAGS)
+
+DEFINE CLANG9PE_IA32_PREFIX          = ENV(CLANG9PE_BIN)
+DEFINE CLANG9PE_X64_PREFIX           = ENV(CLANG9PE_BIN)
+
+DEFINE CLANG9PE_IA32_TARGET          = -target i686-unknown-windows
+DEFINE CLANG9PE_X64_TARGET           = -target x86_64-unknown-windows
+
+DEFINE CLANG9PE_WARNING_OVERRIDES    = -Wno-parentheses-equality -Wno-tautological-compare -Wno-tautological-constant-out-of-range-compare -Wno-empty-body -Wno-unused-const-variable -Wno-varargs -Wno-unknown-warning-option -Wno-microsoft-enum-forward-reference
+DEFINE CLANG9PE_ALL_CC_FLAGS         = DEF(GCC48_ALL_CC_FLAGS) DEF(CLANG9PE_WARNING_OVERRIDES) -fno-stack-protector -mms-bitfields -Wno-address -Wno-shift-negative-value -Wno-unknown-pragmas -Wno-incompatible-library-redeclaration -fno-asynchronous-unwind-tables -mno-implicit-float  -ftrap-function=undefined_behavior_has_been_optimized_away_by_clang -funsigned-char -fno-ms-extensions -Wno-null-dereference -fms-compatibility -mno-stack-arg-probe
+
+###########################
+# CLANG9PE IA32 definitions
+###########################
+*_CLANG9PE_IA32_CC_PATH              = DEF(CLANG9PE_IA32_PREFIX)clang
+*_CLANG9PE_IA32_SLINK_PATH           = DEF(CLANG9PE_IA32_PREFIX)llvm-lib
+*_CLANG9PE_IA32_DLINK_PATH           = DEF(CLANG9PE_IA32_PREFIX)lld-link
+*_CLANG9PE_IA32_ASLDLINK_PATH        = DEF(CLANG9PE_IA32_PREFIX)lld-link
+*_CLANG9PE_IA32_ASM_PATH             = DEF(CLANG9PE_IA32_PREFIX)clang
+*_CLANG9PE_IA32_PP_PATH              = DEF(CLANG9PE_IA32_PREFIX)clang
+*_CLANG9PE_IA32_VFRPP_PATH           = DEF(CLANG9PE_IA32_PREFIX)clang
+*_CLANG9PE_IA32_ASLCC_PATH           = DEF(CLANG9PE_IA32_PREFIX)clang
+*_CLANG9PE_IA32_ASLPP_PATH           = DEF(CLANG9PE_IA32_PREFIX)clang
+*_CLANG9PE_IA32_RC_PATH              = DEF(CLANG9PE_IA32_PREFIX)llvm-rc
+
+*_CLANG9PE_IA32_ASLCC_FLAGS          = DEF(GCC_ASLCC_FLAGS) -m32 -fno-lto DEF(CLANG9PE_IA32_TARGET)
+*_CLANG9PE_IA32_ASM_FLAGS            = DEF(GCC5_ASM_FLAGS) -m32 -march=i386 DEF(CLANG9PE_IA32_TARGET)
+*_CLANG9PE_IA32_OBJCOPY_FLAGS        =
+*_CLANG9PE_IA32_NASM_FLAGS           = -f win32
+*_CLANG9PE_IA32_PP_FLAGS             = DEF(GCC_PP_FLAGS) DEF(CLANG9PE_IA32_TARGET)
+*_CLANG9PE_IA32_ASLPP_FLAGS          = DEF(GCC_ASLPP_FLAGS) DEF(CLANG9PE_IA32_TARGET)
+*_CLANG9PE_IA32_VFRPP_FLAGS          = DEF(GCC_VFRPP_FLAGS) DEF(CLANG9PE_IA32_TARGET)
+
+DEBUG_CLANG9PE_IA32_CC_FLAGS         = DEF(CLANG9PE_ALL_CC_FLAGS) -m32 -Oz -flto -march=i586 DEF(CLANG9PE_IA32_TARGET) -gcodeview
+DEBUG_CLANG9PE_IA32_DLINK_FLAGS      = /NOLOGO /NODEFAULTLIB /IGNORE:4001 /OPT:REF /OPT:ICF=10 /ALIGN:32 /FILEALIGN:32 /SECTION:.xdata,D /SECTION:.pdata,D /MACHINE:X86 /DLL /ENTRY:$(IMAGE_ENTRY_POINT) /SUBSYSTEM:EFI_BOOT_SERVICE_DRIVER /SAFESEH:NO /BASE:0 /DEBUG:GHASH  /lldmap
+DEBUG_CLANG9PE_IA32_DLINK2_FLAGS     =
+
+RELEASE_CLANG9PE_IA32_CC_FLAGS       = DEF(CLANG9PE_ALL_CC_FLAGS) -m32 -Oz -flto -march=i586 DEF(CLANG9PE_IA32_TARGET)
+RELEASE_CLANG9PE_IA32_DLINK_FLAGS    = /NOLOGO /NODEFAULTLIB /IGNORE:4001 /IGNORE:4254 /OPT:REF /OPT:ICF=10 /ALIGN:32 /FILEALIGN:32 /SECTION:.xdata,D /SECTION:.pdata,D /MACHINE:X86 /DLL /ENTRY:$(IMAGE_ENTRY_POINT) /SUBSYSTEM:EFI_BOOT_SERVICE_DRIVER /SAFESEH:NO /BASE:0 /MERGE:.rdata=.data  /lldmap
+RELEASE_CLANG9PE_IA32_DLINK2_FLAGS   = 
+
+NOOPT_CLANG9PE_IA32_CC_FLAGS         = DEF(CLANG9PE_ALL_CC_FLAGS) -m32 -O0 -march=i586 DEF(CLANG9PE_IA32_TARGET) -gcodeview
+NOOPT_CLANG9PE_IA32_DLINK_FLAGS      = /NOLOGO /NODEFAULTLIB /IGNORE:4001 /OPT:REF /OPT:ICF=10 /ALIGN:32 /FILEALIGN:32 /SECTION:.xdata,D /SECTION:.pdata,D /MACHINE:X86 /DLL /ENTRY:$(IMAGE_ENTRY_POINT) /SUBSYSTEM:EFI_BOOT_SERVICE_DRIVER /SAFESEH:NO /BASE:0 /DEBUG:GHASH  /lldmap
+NOOPT_CLANG9PE_IA32_DLINK2_FLAGS     = 
+
+##########################
+# CLANGWIN X64 definitions
+##########################
+*_CLANG9PE_X64_CC_PATH              = DEF(CLANG9PE_X64_PREFIX)clang
+*_CLANG9PE_X64_SLINK_PATH           = DEF(CLANG9PE_X64_PREFIX)llvm-lib
+*_CLANG9PE_X64_DLINK_PATH           = DEF(CLANG9PE_X64_PREFIX)lld-link
+*_CLANG9PE_X64_ASLDLINK_PATH        = DEF(CLANG9PE_X64_PREFIX)lld-link
+*_CLANG9PE_X64_ASM_PATH             = DEF(CLANG9PE_X64_PREFIX)clang
+*_CLANG9PE_X64_PP_PATH              = DEF(CLANG9PE_X64_PREFIX)clang
+*_CLANG9PE_X64_VFRPP_PATH           = DEF(CLANG9PE_X64_PREFIX)clang
+*_CLANG9PE_X64_ASLCC_PATH           = DEF(CLANG9PE_X64_PREFIX)clang
+*_CLANG9PE_X64_ASLPP_PATH           = DEF(CLANG9PE_X64_PREFIX)clang
+*_CLANG9PE_X64_RC_PATH              = DEF(CLANG9PE_IA32_PREFIX)llvm-rc
+
+*_CLANG9PE_X64_ASLCC_FLAGS          = DEF(GCC_ASLCC_FLAGS) -m64 -fno-lto DEF(CLANG9PE_X64_TARGET)
+*_CLANG9PE_X64_ASM_FLAGS            = DEF(GCC5_ASM_FLAGS) -m64 DEF(CLANG9PE_X64_TARGET)
+*_CLANG9PE_X64_OBJCOPY_FLAGS        =
+*_CLANG9PE_X64_NASM_FLAGS           = -f win64
+*_CLANG9PE_X64_PP_FLAGS             = DEF(GCC_PP_FLAGS) DEF(CLANG9PE_X64_TARGET)
+*_CLANG9PE_X64_ASLPP_FLAGS          = DEF(GCC_ASLPP_FLAGS) DEF(CLANG9PE_X64_TARGET)
+*_CLANG9PE_X64_VFRPP_FLAGS          = DEF(GCC_VFRPP_FLAGS) DEF(CLANG9PE_X64_TARGET)
+
+DEBUG_CLANG9PE_X64_CC_FLAGS         = DEF(CLANG9PE_ALL_CC_FLAGS) -m64 "-DEFIAPI=__attribute__((ms_abi))" -mno-red-zone -mcmodel=small -Oz -flto DEF(CLANG9PE_X64_TARGET) -gcodeview
+DEBUG_CLANG9PE_X64_DLINK_FLAGS      = /NOLOGO /NODEFAULTLIB /IGNORE:4001 /OPT:REF /OPT:ICF=10 /ALIGN:32 /FILEALIGN:32 /SECTION:.xdata,D /SECTION:.pdata,D /Machine:X64 /DLL /ENTRY:$(IMAGE_ENTRY_POINT) /SUBSYSTEM:EFI_BOOT_SERVICE_DRIVER /SAFESEH:NO /BASE:0 /DEBUG:GHASH  /lldmap
+DEBUG_CLANG9PE_X64_DLINK2_FLAGS     = 
+
+RELEASE_CLANG9PE_X64_CC_FLAGS       = DEF(CLANG9PE_ALL_CC_FLAGS) -m64 "-DEFIAPI=__attribute__((ms_abi))" -mno-red-zone -mcmodel=small -Oz -flto DEF(CLANG9PE_X64_TARGET)
+RELEASE_CLANG9PE_X64_DLINK_FLAGS    = /NOLOGO /NODEFAULTLIB /IGNORE:4001 /IGNORE:4254 /OPT:REF /OPT:ICF=10 /ALIGN:32 /FILEALIGN:32 /SECTION:.xdata,D /SECTION:.pdata,D /Machine:X64 /DLL /ENTRY:$(IMAGE_ENTRY_POINT) /SUBSYSTEM:EFI_BOOT_SERVICE_DRIVER /SAFESEH:NO /BASE:0 /MERGE:.rdata=.data  /lldmap
+RELEASE_CLANG9PE_X64_DLINK2_FLAGS   = 
+
+NOOPT_CLANG9PE_X64_CC_FLAGS         = DEF(CLANG9PE_ALL_CC_FLAGS) -m64 "-DEFIAPI=__attribute__((ms_abi))" -mno-red-zone -mcmodel=small -O0 DEF(CLANG9PE_X64_TARGET) -gcodeview
+NOOPT_CLANG9PE_X64_DLINK_FLAGS      = /NOLOGO /NODEFAULTLIB /IGNORE:4001 /OPT:REF /OPT:ICF=10 /ALIGN:32 /FILEALIGN:32 /SECTION:.xdata,D /SECTION:.pdata,D /Machine:X64 /DLL /ENTRY:$(IMAGE_ENTRY_POINT) /SUBSYSTEM:EFI_BOOT_SERVICE_DRIVER /SAFESEH:NO /BASE:0 /DEBUG:GHASH  /lldmap
+NOOPT_CLANG9PE_X64_DLINK2_FLAGS     = 
 
 
 #
@@ -2590,8 +2692,8 @@ RELEASE_XCODE5_X64_DLINK_FLAGS      = -arch x86_64 -u _$(IMAGE_ENTRY_POINT) -e _
   NOOPT_XCODE5_X64_ASM_FLAGS  = -arch x86_64 -g
 RELEASE_XCODE5_X64_ASM_FLAGS  = -arch x86_64
       *_XCODE5_X64_NASM_FLAGS = -f macho64
-*_XCODE5_*_PP_FLAGS         = -E -x assembler-with-cpp -include $(DEST_DIR_DEBUG)/AutoGen.h
-*_XCODE5_*_VFRPP_FLAGS      = -x c -E -P -DVFRCOMPILE -include $(DEST_DIR_DEBUG)/$(MODULE_NAME)StrDefs.h
+*_XCODE5_*_PP_FLAGS         = -E -x assembler-with-cpp -include AutoGen.h
+*_XCODE5_*_VFRPP_FLAGS      = -x c -E -P -DVFRCOMPILE -include $(MODULE_NAME)StrDefs.h
 
   DEBUG_XCODE5_X64_CC_FLAGS   = -target x86_64-pc-win32-macho -c -g -gdwarf -Os       -Wall -Werror -Wextra -include AutoGen.h -funsigned-char -fno-ms-extensions -fno-stack-protector -fno-builtin -fshort-wchar -mno-implicit-float -mms-bitfields -Wno-unused-parameter -Wno-missing-braces -Wno-missing-field-initializers -Wno-tautological-compare -Wno-sign-compare -Wno-varargs -ftrap-function=undefined_behavior_has_been_optimized_away_by_clang -D NO_MSABI_VA_FUNCS $(PLATFORM_FLAGS)
   NOOPT_XCODE5_X64_CC_FLAGS   = -target x86_64-pc-win32-macho -c -g -gdwarf -O0       -Wall -Werror -Wextra -include AutoGen.h -funsigned-char -fno-ms-extensions -fno-stack-protector -fno-builtin -fshort-wchar -mno-implicit-float -mms-bitfields -Wno-unused-parameter -Wno-missing-braces -Wno-missing-field-initializers -Wno-tautological-compare -Wno-sign-compare -Wno-varargs -ftrap-function=undefined_behavior_has_been_optimized_away_by_clang -D NO_MSABI_VA_FUNCS $(PLATFORM_FLAGS)
@@ -2630,7 +2732,7 @@ RELEASE_RVCT_ARM_DLINK_FLAGS     = $(ARCHDLINK_FLAGS) DEF(RVCT_ALL_DLINK_FLAGS)
 
 *_RVCT_ARM_ASM_FLAGS       = $(ARCHASM_FLAGS) $(PLATFORM_FLAGS) DEF(RVCT_ALL_ASM_FLAGS)
 *_RVCT_ARM_PP_FLAGS        = $(ARCHCC_FLAGS) $(PLATFORM_FLAGS) -E --preinclude AutoGen.h
-*_RVCT_ARM_VFRPP_FLAGS     = $(ARCHCC_FLAGS) $(PLATFORM_FLAGS) -E  -DVFRCOMPILE --preinclude $(DEST_DIR_DEBUG)/$(MODULE_NAME)StrDefs.h
+*_RVCT_ARM_VFRPP_FLAGS     = $(ARCHCC_FLAGS) $(PLATFORM_FLAGS) -E  -DVFRCOMPILE --preinclude $(MODULE_NAME)StrDefs.h
 *_RVCT_ARM_MAKE_PATH       = nmake /NOLOGO
 *_RVCT_ARM_SLINK_FLAGS     = --partial -o
   DEBUG_RVCT_ARM_CC_FLAGS  = $(ARCHCC_FLAGS) $(PLATFORM_FLAGS) DEF(RVCT_ALL_CC_FLAGS) -O1 -g
@@ -2671,7 +2773,7 @@ RELEASE_RVCTLINUX_ARM_DLINK_FLAGS   = $(ARCHDLINK_FLAGS) DEF(RVCT_ALL_DLINK_FLAG
 
 *_RVCTLINUX_ARM_ASM_FLAGS       = $(ARCHASM_FLAGS) $(PLATFORM_FLAGS) DEF(RVCT_ALL_ASM_FLAGS)
 *_RVCTLINUX_ARM_PP_FLAGS        = $(ARCHCC_FLAGS) $(PLATFORM_FLAGS) -E
-*_RVCTLINUX_ARM_VFRPP_FLAGS     = $(ARCHCC_FLAGS) $(PLATFORM_FLAGS) -E  -DVFRCOMPILE --preinclude $(DEST_DIR_DEBUG)/$(MODULE_NAME)StrDefs.h
+*_RVCTLINUX_ARM_VFRPP_FLAGS     = $(ARCHCC_FLAGS) $(PLATFORM_FLAGS) -E  -DVFRCOMPILE --preinclude $(MODULE_NAME)StrDefs.h
 *_RVCTLINUX_ARM_SLINK_FLAGS     = --partial -o
   DEBUG_RVCTLINUX_ARM_CC_FLAGS  = $(ARCHCC_FLAGS) $(PLATFORM_FLAGS) DEF(RVCT_ALL_CC_FLAGS) -O1 -g
 RELEASE_RVCTLINUX_ARM_CC_FLAGS  = $(ARCHCC_FLAGS) $(PLATFORM_FLAGS) --diag_suppress=550 DEF(RVCT_ALL_CC_FLAGS) -O2
@@ -2718,7 +2820,7 @@ RELEASE_RVCTCYGWIN_ARM_DLINK_FLAGS     = "$(DLINKPATH_FLAG)" $(ARCHDLINK_FLAGS)
 
 *_RVCTCYGWIN_ARM_ASM_FLAGS       = "$(ASMPATH_FLAG)" $(ARCHASM_FLAGS) $(PLATFORM_FLAGS) DEF(RVCT_ALL_ASM_FLAGS)
 *_RVCTCYGWIN_ARM_PP_FLAGS        = "$(CCPATH_FLAG)" $(ARCHCC_FLAGS) $(PLATFORM_FLAGS) -E
-*_RVCTCYGWIN_ARM_VFRPP_FLAGS     = "$(CCPATH_FLAG)" $(ARCHCC_FLAGS) $(PLATFORM_FLAGS) -E  -DVFRCOMPILE --preinclude `cygpath -m $(DEST_DIR_DEBUG)/$(MODULE_NAME)StrDefs.h`
+*_RVCTCYGWIN_ARM_VFRPP_FLAGS     = "$(CCPATH_FLAG)" $(ARCHCC_FLAGS) $(PLATFORM_FLAGS) -E  -DVFRCOMPILE --preinclude `cygpath -m $(MODULE_NAME)StrDefs.h`
 *_RVCTCYGWIN_ARM_MAKE_PATH       = make
 *_RVCTCYGWIN_ARM_SLINK_FLAGS     = "$(SLINKPATH_FLAG)" --partial -o
   DEBUG_RVCTCYGWIN_ARM_CC_FLAGS  = "$(CCPATH_FLAG)" $(ARCHCC_FLAGS) $(PLATFORM_FLAGS) DEF(RVCT_ALL_CC_FLAGS) -O1 -g
diff --git a/BaseTools/Source/C/GenFw/GenFw.c b/BaseTools/Source/C/GenFw/GenFw.c
index c99782b78eca..d8d3360c2440 100644
--- a/BaseTools/Source/C/GenFw/GenFw.c
+++ b/BaseTools/Source/C/GenFw/GenFw.c
@@ -653,7 +653,11 @@ PeCoffConvertImageToXip (
     //
     // Make the size of raw data in section header alignment.
     //
-    SectionHeader->SizeOfRawData = (SectionHeader->Misc.VirtualSize + PeHdr->Pe32.OptionalHeader.FileAlignment - 1) & (~(PeHdr->Pe32.OptionalHeader.FileAlignment - 1));
+    SectionSize = (SectionHeader->Misc.VirtualSize + PeHdr->Pe32.OptionalHeader.FileAlignment - 1) & (~(PeHdr->Pe32.OptionalHeader.FileAlignment - 1));
+    if (SectionSize < SectionHeader->SizeOfRawData) {
+      SectionHeader->SizeOfRawData = SectionSize;
+    }
+    
     SectionHeader->PointerToRawData = SectionHeader->VirtualAddress;
   }
 
@@ -999,7 +1003,7 @@ Routine Description:
     CopyMem (
       FileBuffer + SectionHeader->PointerToRawData,
       (VOID*) (UINTN) (ImageContext.ImageAddress + SectionHeader->VirtualAddress),
-      SectionHeader->SizeOfRawData
+      SectionHeader->SizeOfRawData < SectionHeader->Misc.VirtualSize ? SectionHeader->SizeOfRawData : SectionHeader->Misc.VirtualSize
       );
   }
 
diff --git a/CryptoPkg/Library/BaseCryptLib/BaseCryptLib.inf b/CryptoPkg/Library/BaseCryptLib/BaseCryptLib.inf
index 8d4988e8c6b4..a9b3fc513c09 100644
--- a/CryptoPkg/Library/BaseCryptLib/BaseCryptLib.inf
+++ b/CryptoPkg/Library/BaseCryptLib/BaseCryptLib.inf
@@ -101,5 +101,6 @@
 
   GCC:*_CLANG35_*_CC_FLAGS = -std=c99
   GCC:*_CLANG38_*_CC_FLAGS = -std=c99
+  GCC:*_CLANG9PE_*_CC_FLAGS = -std=c99 -Wno-error=incompatible-pointer-types
 
   XCODE:*_*_*_CC_FLAGS = -std=c99
diff --git a/CryptoPkg/Library/BaseCryptLib/PeiCryptLib.inf b/CryptoPkg/Library/BaseCryptLib/PeiCryptLib.inf
index 3da8bd848017..11cfcbf726a3 100644
--- a/CryptoPkg/Library/BaseCryptLib/PeiCryptLib.inf
+++ b/CryptoPkg/Library/BaseCryptLib/PeiCryptLib.inf
@@ -96,5 +96,6 @@
 
   GCC:*_CLANG35_*_CC_FLAGS = -std=c99
   GCC:*_CLANG38_*_CC_FLAGS = -std=c99
+  GCC:*_CLANG9PE_*_CC_FLAGS = -std=c99 -Wno-error=incompatible-pointer-types
 
   XCODE:*_*_*_CC_FLAGS = -std=c99
diff --git a/CryptoPkg/Library/BaseCryptLib/RuntimeCryptLib.inf b/CryptoPkg/Library/BaseCryptLib/RuntimeCryptLib.inf
index 21a481eb7767..d1afd0ea6d1c 100644
--- a/CryptoPkg/Library/BaseCryptLib/RuntimeCryptLib.inf
+++ b/CryptoPkg/Library/BaseCryptLib/RuntimeCryptLib.inf
@@ -107,5 +107,6 @@
 
   GCC:*_CLANG35_*_CC_FLAGS = -std=c99
   GCC:*_CLANG38_*_CC_FLAGS = -std=c99
+  GCC:*_CLANG9PE_*_CC_FLAGS = -std=c99 -Wno-error=incompatible-pointer-types
 
   XCODE:*_*_*_CC_FLAGS = -std=c99
diff --git a/CryptoPkg/Library/BaseCryptLib/SmmCryptLib.inf b/CryptoPkg/Library/BaseCryptLib/SmmCryptLib.inf
index 7c187e21b3b9..0eeefb75affe 100644
--- a/CryptoPkg/Library/BaseCryptLib/SmmCryptLib.inf
+++ b/CryptoPkg/Library/BaseCryptLib/SmmCryptLib.inf
@@ -104,3 +104,4 @@
 
   GCC:*_CLANG35_*_CC_FLAGS = -std=c99
   GCC:*_CLANG38_*_CC_FLAGS = -std=c99
+  GCC:*_CLANG9PE_*_CC_FLAGS = -std=c99 -Wno-error=incompatible-pointer-types
diff --git a/CryptoPkg/Library/IntrinsicLib/MemoryIntrinsics.c b/CryptoPkg/Library/IntrinsicLib/MemoryIntrinsics.c
index 6e4d4a68cc3f..94fe341bec9d 100644
--- a/CryptoPkg/Library/IntrinsicLib/MemoryIntrinsics.c
+++ b/CryptoPkg/Library/IntrinsicLib/MemoryIntrinsics.c
@@ -2,7 +2,7 @@
   Intrinsic Memory Routines Wrapper Implementation for OpenSSL-based
   Cryptographic Library.
 
-Copyright (c) 2010 - 2018, Intel Corporation. All rights reserved.<BR>
+Copyright (c) 2010 - 2019, Intel Corporation. All rights reserved.<BR>
 SPDX-License-Identifier: BSD-2-Clause-Patent
 
 **/
@@ -13,9 +13,15 @@ SPDX-License-Identifier: BSD-2-Clause-Patent
 
 typedef UINTN  size_t;
 
+#if defined(__GNUC__) || defined(__clang__)
+  #define GLOBAL_USED __attribute__((used))
+#else
+  #define GLOBAL_USED
+#endif
+
 /* OpenSSL will use floating point support, and C compiler produces the _fltused
    symbol by default. Simply define this symbol here to satisfy the linker. */
-int _fltused = 1;
+int  GLOBAL_USED _fltused = 1;
 
 /* Sets buffers to a specified character */
 void * memset (void *dest, int ch, size_t count)
diff --git a/CryptoPkg/Library/OpensslLib/OpensslLib.inf b/CryptoPkg/Library/OpensslLib/OpensslLib.inf
index 7432321fd431..9cb7e71a5b69 100644
--- a/CryptoPkg/Library/OpensslLib/OpensslLib.inf
+++ b/CryptoPkg/Library/OpensslLib/OpensslLib.inf
@@ -662,6 +662,7 @@
   GCC:*_*_AARCH64_CC_FLAGS = $(OPENSSL_FLAGS) -Wno-error=maybe-uninitialized -Wno-format -Wno-error=unused-but-set-variable
   GCC:*_CLANG35_*_CC_FLAGS = -std=c99 -Wno-error=uninitialized
   GCC:*_CLANG38_*_CC_FLAGS = -std=c99 -Wno-error=uninitialized
+  GCC:*_CLANG9PE_*_CC_FLAGS = -std=c99 -Wno-error=uninitialized -Wno-error=incompatible-pointer-types -Wno-error=pointer-sign -Wno-error=implicit-function-declaration -Wno-error=ignored-pragma-optimize
 
   # suppress the following warnings in openssl so we don't break the build with warnings-as-errors:
   # 1295: Deprecated declaration <entity> - give arg types
diff --git a/CryptoPkg/Library/OpensslLib/OpensslLibCrypto.inf b/CryptoPkg/Library/OpensslLib/OpensslLibCrypto.inf
index 8134b45eda25..ba0ca95d61e0 100644
--- a/CryptoPkg/Library/OpensslLib/OpensslLibCrypto.inf
+++ b/CryptoPkg/Library/OpensslLib/OpensslLibCrypto.inf
@@ -610,6 +610,7 @@
   GCC:*_*_AARCH64_CC_FLAGS = $(OPENSSL_FLAGS) -Wno-error=maybe-uninitialized -Wno-format -Wno-error=unused-but-set-variable
   GCC:*_CLANG35_*_CC_FLAGS = -std=c99 -Wno-error=uninitialized
   GCC:*_CLANG38_*_CC_FLAGS = -std=c99 -Wno-error=uninitialized
+  GCC:*_CLANG9PE_*_CC_FLAGS = -std=c99 -Wno-error=uninitialized -Wno-error=incompatible-pointer-types -Wno-error=pointer-sign -Wno-error=implicit-function-declaration -Wno-error=ignored-pragma-optimize
 
   # suppress the following warnings in openssl so we don't break the build with warnings-as-errors:
   # 1295: Deprecated declaration <entity> - give arg types
diff --git a/EmulatorPkg/EmulatorPkg.dsc b/EmulatorPkg/EmulatorPkg.dsc
index 20f118771393..9d978f46dc56 100644
--- a/EmulatorPkg/EmulatorPkg.dsc
+++ b/EmulatorPkg/EmulatorPkg.dsc
@@ -237,7 +237,7 @@
 
 [Components]
 !if "IA32" in $(ARCH) || "X64" in $(ARCH)
-  !if "MSFT" in $(FAMILY)
+  !if "MSFT" in $(FAMILY) || "CLANG9PE" in $(TOOL_CHAIN_TAG)
     ##
     #  Emulator, OS WIN application
     ##
@@ -377,7 +377,7 @@
 
   FatPkg/EnhancedFatDxe/Fat.inf
 
-!if "XCODE5" not in $(TOOL_CHAIN_TAG)
+!if "XCODE5" not in $(TOOL_CHAIN_TAG) and "CLANG9PE" not in $(TOOL_CHAIN_TAG)
   ShellPkg/DynamicCommand/TftpDynamicCommand/TftpDynamicCommand.inf {
     <PcdsFixedAtBuild>
       gEfiShellPkgTokenSpaceGuid.PcdShellLibAutoInitialize|FALSE
@@ -419,7 +419,11 @@
 
   MSFT:DEBUG_*_*_CC_FLAGS = /Od /Oy-
   MSFT:NOOPT_*_*_CC_FLAGS = /Od /Oy-
+  CLANGPE:DEBUG_*_*_CC_FLAGS =-O0 -D UNICODE -Wno-unused-command-line-argument -Wno-incompatible-pointer-types -Wno-enum-conversion -Wno-incompatible-pointer-types -Wno-sometimes-uninitialized -Wno-constant-conversion -Wno-main-return-type
 
   MSFT:*_*_*_DLINK_FLAGS     = /ALIGN:4096 /FILEALIGN:4096 /SUBSYSTEM:CONSOLE
   MSFT:DEBUG_*_*_DLINK_FLAGS = /EXPORT:InitializeDriver=$(IMAGE_ENTRY_POINT) /BASE:0x10000
   MSFT:NOOPT_*_*_DLINK_FLAGS = /EXPORT:InitializeDriver=$(IMAGE_ENTRY_POINT) /BASE:0x10000
+  CLANGPE:*_*_*_DLINK_FLAGS     = /ALIGN:4096 /FILEALIGN:4096 /SUBSYSTEM:CONSOLE
+  CLANGPE:DEBUG_*_*_DLINK_FLAGS = /EXPORT:InitializeDriver=$(IMAGE_ENTRY_POINT) /BASE:0x10000
+  CLANGPE:NOOPT_*_*_DLINK_FLAGS = /EXPORT:InitializeDriver=$(IMAGE_ENTRY_POINT) /BASE:0x10000
diff --git a/EmulatorPkg/EmulatorPkg.fdf b/EmulatorPkg/EmulatorPkg.fdf
index 295f6f1db8ab..473289ca72a5 100644
--- a/EmulatorPkg/EmulatorPkg.fdf
+++ b/EmulatorPkg/EmulatorPkg.fdf
@@ -196,7 +196,7 @@ INF  EmulatorPkg/EmuSnpDxe/EmuSnpDxe.inf
 
 INF FatPkg/EnhancedFatDxe/Fat.inf
 
-!if "XCODE5" not in $(TOOL_CHAIN_TAG)
+!if "XCODE5" not in $(TOOL_CHAIN_TAG) and "CLANG9PE" not in $(TOOL_CHAIN_TAG)
 INF  ShellPkg/DynamicCommand/TftpDynamicCommand/TftpDynamicCommand.inf
 !endif
 INF  ShellPkg/Application/Shell/Shell.inf
diff --git a/EmulatorPkg/Win/Host/WinHost.c b/EmulatorPkg/Win/Host/WinHost.c
index 9aba3c89593d..d51a96de7b31 100644
--- a/EmulatorPkg/Win/Host/WinHost.c
+++ b/EmulatorPkg/Win/Host/WinHost.c
@@ -356,7 +356,7 @@ Routine Description:
 INTN
 EFIAPI
 main (
-  IN  INTN  Argc,
+  IN  INT  Argc,
   IN  CHAR8 **Argv,
   IN  CHAR8 **Envp
   )
@@ -405,9 +405,6 @@ Routine Description:
     AdjustTokenPrivileges(Token, FALSE, &TokenPrivileges, 0, (PTOKEN_PRIVILEGES) NULL, 0);
   }
 
-  MemorySizeStr      = (CHAR16 *) PcdGetPtr (PcdEmuMemorySize);
-  FirmwareVolumesStr = (CHAR16 *) PcdGetPtr (PcdEmuFirmwareVolume);
-
   SecPrint ("\n\rEDK II WIN Host Emulation Environment from http://www.tianocore.org/edk2/\n\r");
 
   //
@@ -423,6 +420,12 @@ Routine Description:
       SetProcessAffinityMask (GetCurrentProcess (), (INTN)(BIT0 << LowBit));
     }
   }
+  
+  //
+  // Move PCD getting late
+  //
+  MemorySizeStr      = (CHAR16 *) PcdGetPtr (PcdEmuMemorySize);
+  FirmwareVolumesStr = (CHAR16 *) PcdGetPtr (PcdEmuFirmwareVolume);
 
   //
   // Make some Windows calls to Set the process to the highest priority in the
diff --git a/EmulatorPkg/Win/Host/WinHost.inf b/EmulatorPkg/Win/Host/WinHost.inf
index 631d5a647022..dad9278fa3d6 100644
--- a/EmulatorPkg/Win/Host/WinHost.inf
+++ b/EmulatorPkg/Win/Host/WinHost.inf
@@ -95,3 +95,9 @@
   MSFT:*_VS2017_X64_DLINK_FLAGS      = /LIBPATH:"%VCToolsInstallDir%lib\x64" /LIBPATH:"%UniversalCRTSdkDir%lib\%UCRTVersion%\ucrt\x64" /LIBPATH:"%WindowsSdkDir%lib\%WindowsSDKLibVersion%\um\x64" /NOLOGO /SUBSYSTEM:CONSOLE /NODEFAULTLIB /IGNORE:4086 /MAP /OPT:REF /DEBUG /MACHINE:AMD64 /LTCG Kernel32.lib MSVCRTD.lib vcruntimed.lib ucrtd.lib Gdi32.lib User32.lib Winmm.lib Advapi32.lib
   MSFT:*_*_X64_ASM_FLAGS            == /nologo /W3 /WX /c /Cx /Zd /W0 /Zi
   MSFT:*_*_X64_ASMLINK_FLAGS        == /link /nologo
+
+  CLANGPE:*_*_X64_DLINK_FLAGS == /out:"$(BIN_DIR)\$(BASE_NAME).exe" /base:0x10000000 /pdb:"$(BIN_DIR)\$(BASE_NAME).pdb"  /LIBPATH:"%UniversalCRTSdkDir%lib\%UCRTVersion%\ucrt\x64" /LIBPATH:"%WindowsSdkDir%lib\%WindowsSDKLibVersion%\um\x64" /LIBPATH:"%VCToolsInstallDir%lib\x64"   /NOLOGO /SUBSYSTEM:CONSOLE /NODEFAULTLIB /IGNORE:4086  /OPT:REF /DEBUG /MACHINE:AMD64 Kernel32.lib MSVCRTD.lib vcruntimed.lib ucrtd.lib Gdi32.lib User32.lib Winmm.lib Advapi32.lib /lldmap  /EXPORT:InitializeDriver=_ModuleEntryPoint
+  CLANGPE:*_*_X64_CC_FLAGS == -m64 -g -fshort-wchar -fno-strict-aliasing -Wall -c -include AutoGen.h -D _CRT_SECURE_NO_WARNINGS -Wnonportable-include-path  -D UNICODE -D _CRT_SECURE_NO_DEPRECATE
+
+  CLANGPE:*_*_IA32_DLINK_FLAGS == /out:"$(BIN_DIR)\$(BASE_NAME).exe" /base:0x10000000 /pdb:"$(BIN_DIR)\$(BASE_NAME).pdb" /LIBPATH:"%UniversalCRTSdkDir%lib\%UCRTVersion%\ucrt\x86" /LIBPATH:"%WindowsSdkDir%lib\%WindowsSDKLibVersion%\um\x86" /LIBPATH:"%VCToolsInstallDir%ib\x86"   /NOLOGO /SUBSYSTEM:CONSOLE /NODEFAULTLIB /IGNORE:4086  /OPT:REF /DEBUG /MACHINE:I386 Kernel32.lib MSVCRTD.lib vcruntimed.lib ucrtd.lib Gdi32.lib User32.lib Winmm.lib Advapi32.lib /lldmap  /EXPORT:InitializeDriver=_ModuleEntryPoint
+  CLANGPE:*_*_IA32_CC_FLAGS == -m32 -g -fshort-wchar -fno-strict-aliasing -Wall -c -include AutoGen.h -D _CRT_SECURE_NO_WARNINGS -Wnonportable-include-path  -D UNICODE -D _CRT_SECURE_NO_DEPRECATE
diff --git a/MdeModulePkg/Library/LzmaCustomDecompressLib/Sdk/C/7zTypes.h b/MdeModulePkg/Library/LzmaCustomDecompressLib/Sdk/C/7zTypes.h
index a5fcb50baea3..3ce087ecf710 100644
--- a/MdeModulePkg/Library/LzmaCustomDecompressLib/Sdk/C/7zTypes.h
+++ b/MdeModulePkg/Library/LzmaCustomDecompressLib/Sdk/C/7zTypes.h
@@ -118,7 +118,7 @@ typedef int Bool;
 #define MY_STD_CALL
 #endif
 
-#ifdef _MSC_VER
+#if defined(_MSC_VER) && !defined(__clang__)
 
 #if _MSC_VER >= 1300
 #define MY_NO_INLINE __declspec(noinline)
diff --git a/MdeModulePkg/Universal/RegularExpressionDxe/RegularExpressionDxe.inf b/MdeModulePkg/Universal/RegularExpressionDxe/RegularExpressionDxe.inf
index 883d5f112765..818f1f79b129 100644
--- a/MdeModulePkg/Universal/RegularExpressionDxe/RegularExpressionDxe.inf
+++ b/MdeModulePkg/Universal/RegularExpressionDxe/RegularExpressionDxe.inf
@@ -107,6 +107,9 @@
   # Oniguruma: tag_end in parse_callout_of_name
   GCC:*_*_*_CC_FLAGS = -Wno-error=maybe-uninitialized
 
+  # Oniguruma: implicit conversion from 'UINTN' (aka 'unsigned long long') to 'long'
+  GCC:*_CLANG9PE_*_CC_FLAGS = -Wno-error=constant-conversion
+
   # Not add -Wno-error=maybe-uninitialized option for XCODE
   # XCODE doesn't know this option
   XCODE:*_*_*_CC_FLAGS =
diff --git a/MdePkg/Include/Base.h b/MdePkg/Include/Base.h
index ce20b5f01dce..9498dfe0d9fe 100644
--- a/MdePkg/Include/Base.h
+++ b/MdePkg/Include/Base.h
@@ -673,9 +673,9 @@ typedef char* VA_LIST;
 #define VA_END(Marker)                  (Marker = (VA_LIST) 0)
 #define VA_COPY(Dest, Start)            ((void)((Dest) = (Start)))
 
-#elif defined(__GNUC__)
+#elif defined(__GNUC__) || defined(__clang__)
 
-#if defined(MDE_CPU_X64) && !defined(NO_MSABI_VA_FUNCS)
+#if defined(MDE_CPU_X64) && !defined(NO_MSABI_VA_FUNCS) && !defined(__clang__)
 //
 // X64 only. Use MS ABI version of GCC built-in macros for variable argument lists.
 //
@@ -1270,7 +1270,7 @@ typedef UINTN RETURN_STATUS;
 
   **/
   #define RETURN_ADDRESS(L)     ((L == 0) ? _ReturnAddress() : (VOID *) 0)
-#elif defined(__GNUC__)
+#elif defined (__GNUC__) || defined (__clang__)
   void * __builtin_return_address (unsigned int level);
   /**
     Get the return address of the calling function.
diff --git a/MdePkg/Include/Ia32/ProcessorBind.h b/MdePkg/Include/Ia32/ProcessorBind.h
index 497c58b33b73..fa4b7e8e98cb 100644
--- a/MdePkg/Include/Ia32/ProcessorBind.h
+++ b/MdePkg/Include/Ia32/ProcessorBind.h
@@ -281,7 +281,7 @@ typedef INT32   INTN;
   /// Microsoft* compiler specific method for EFIAPI calling convention.
   ///
   #define EFIAPI __cdecl
-#elif defined(__GNUC__)
+#elif defined(__GNUC__) || defined(__clang__)
   ///
   /// GCC specific method for EFIAPI calling convention.
   ///
@@ -294,7 +294,7 @@ typedef INT32   INTN;
   #define EFIAPI
 #endif
 
-#if defined(__GNUC__)
+#if defined(__GNUC__) || defined(__clang__)
   ///
   /// For GNU assembly code, .global or .globl can declare global symbols.
   /// Define this macro to unify the usage.
diff --git a/MdePkg/Include/Library/DebugLib.h b/MdePkg/Include/Library/DebugLib.h
index f1d55cf62b0e..3c54e07ab6ae 100644
--- a/MdePkg/Include/Library/DebugLib.h
+++ b/MdePkg/Include/Library/DebugLib.h
@@ -289,8 +289,11 @@ DebugPrintLevelEnabled (
   @param  Expression  Boolean expression that evaluated to FALSE
 
 **/
+#ifdef __clang__
+#define _ASSERT(Expression)  DebugAssert (__FILE_NAME__, __LINE__, #Expression)
+#else
 #define _ASSERT(Expression)  DebugAssert (__FILE__, __LINE__, #Expression)
-
+#endif
 
 /**
   Internal worker macro that calls DebugPrint().
diff --git a/MdePkg/Include/X64/ProcessorBind.h b/MdePkg/Include/X64/ProcessorBind.h
index 6f65acd60939..387e9c5c9c19 100644
--- a/MdePkg/Include/X64/ProcessorBind.h
+++ b/MdePkg/Include/X64/ProcessorBind.h
@@ -313,7 +313,7 @@ typedef INT64   INTN;
   #define EFIAPI
 #endif
 
-#if defined(__GNUC__)
+#if defined(__GNUC__) || defined(__clang__)
   ///
   /// For GNU assembly code, .global or .globl can declare global symbols.
   /// Define this macro to unify the usage.
diff --git a/MdePkg/Library/BaseIoLibIntrinsic/IoLibGcc.c b/MdePkg/Library/BaseIoLibIntrinsic/IoLibGcc.c
index 055f0a947ece..b3a1a2025663 100644
--- a/MdePkg/Library/BaseIoLibIntrinsic/IoLibGcc.c
+++ b/MdePkg/Library/BaseIoLibIntrinsic/IoLibGcc.c
@@ -32,7 +32,6 @@
   @return The value read.
 
 **/
-__inline__
 UINT8
 EFIAPI
 IoRead8 (
@@ -60,7 +59,6 @@ IoRead8 (
   @return The value written the I/O port.
 
 **/
-__inline__
 UINT8
 EFIAPI
 IoWrite8 (
@@ -87,7 +85,6 @@ IoWrite8 (
   @return The value read.
 
 **/
-__inline__
 UINT16
 EFIAPI
 IoRead16 (
@@ -117,7 +114,6 @@ IoRead16 (
   @return The value written the I/O port.
 
 **/
-__inline__
 UINT16
 EFIAPI
 IoWrite16 (
@@ -145,7 +141,6 @@ IoWrite16 (
   @return The value read.
 
 **/
-__inline__
 UINT32
 EFIAPI
 IoRead32 (
@@ -175,7 +170,6 @@ IoRead32 (
   @return The value written the I/O port.
 
 **/
-__inline__
 UINT32
 EFIAPI
 IoWrite32 (
diff --git a/OvmfPkg/OvmfPkgIa32.dsc b/OvmfPkg/OvmfPkgIa32.dsc
index 66e944436a69..7af58f4795c8 100644
--- a/OvmfPkg/OvmfPkgIa32.dsc
+++ b/OvmfPkg/OvmfPkgIa32.dsc
@@ -66,7 +66,7 @@
   GCC:RELEASE_*_*_CC_FLAGS             = -DMDEPKG_NDEBUG
   INTEL:RELEASE_*_*_CC_FLAGS           = /D MDEPKG_NDEBUG
   MSFT:RELEASE_*_*_CC_FLAGS            = /D MDEPKG_NDEBUG
-!if $(TOOL_CHAIN_TAG) != "XCODE5"
+!if $(TOOL_CHAIN_TAG) != "XCODE5" && $(TOOL_CHAIN_TAG) != "CLANG9PE"
   GCC:*_*_*_CC_FLAGS                   = -mno-mmx -mno-sse
 !endif
 
@@ -80,12 +80,14 @@
 [BuildOptions.common.EDKII.DXE_RUNTIME_DRIVER]
   GCC:*_*_*_DLINK_FLAGS = -z common-page-size=0x1000
   XCODE:*_*_*_DLINK_FLAGS =
+  CLANGPE: *_*_*_DLINK_FLAGS = /ALIGN:4096
 
 # Force PE/COFF sections to be aligned at 4KB boundaries to support page level
 # protection of DXE_SMM_DRIVER/SMM_CORE modules
 [BuildOptions.common.EDKII.DXE_SMM_DRIVER, BuildOptions.common.EDKII.SMM_CORE]
   GCC:*_*_*_DLINK_FLAGS = -z common-page-size=0x1000
   XCODE:*_*_*_DLINK_FLAGS =
+  CLANGPE: *_*_*_DLINK_FLAGS = /ALIGN:4096
 
 ################################################################################
 #
@@ -804,7 +806,7 @@
   OvmfPkg/Csm/Csm16/Csm16.inf
 !endif
 
-!if $(TOOL_CHAIN_TAG) != "XCODE5"
+!if $(TOOL_CHAIN_TAG) != "XCODE5" && $(TOOL_CHAIN_TAG) != "CLANG9PE"
   ShellPkg/DynamicCommand/TftpDynamicCommand/TftpDynamicCommand.inf {
     <PcdsFixedAtBuild>
       gEfiShellPkgTokenSpaceGuid.PcdShellLibAutoInitialize|FALSE
diff --git a/OvmfPkg/OvmfPkgIa32.fdf b/OvmfPkg/OvmfPkgIa32.fdf
index 785affeb90c8..4176e1fe1771 100644
--- a/OvmfPkg/OvmfPkgIa32.fdf
+++ b/OvmfPkg/OvmfPkgIa32.fdf
@@ -278,7 +278,7 @@ INF  MdeModulePkg/Universal/Acpi/BootGraphicsResourceTableDxe/BootGraphicsResour
 INF  FatPkg/EnhancedFatDxe/Fat.inf
 INF  MdeModulePkg/Universal/Disk/UdfDxe/UdfDxe.inf
 
-!if $(TOOL_CHAIN_TAG) != "XCODE5"
+!if $(TOOL_CHAIN_TAG) != "XCODE5" && $(TOOL_CHAIN_TAG) != "CLANG9PE"
 INF  ShellPkg/DynamicCommand/TftpDynamicCommand/TftpDynamicCommand.inf
 !endif
 INF  ShellPkg/Application/Shell/Shell.inf
diff --git a/OvmfPkg/OvmfPkgIa32X64.dsc b/OvmfPkg/OvmfPkgIa32X64.dsc
index 51c2bfb44f14..012869b66460 100644
--- a/OvmfPkg/OvmfPkgIa32X64.dsc
+++ b/OvmfPkg/OvmfPkgIa32X64.dsc
@@ -66,7 +66,7 @@
   GCC:RELEASE_*_*_CC_FLAGS             = -DMDEPKG_NDEBUG
   INTEL:RELEASE_*_*_CC_FLAGS           = /D MDEPKG_NDEBUG
   MSFT:RELEASE_*_*_CC_FLAGS            = /D MDEPKG_NDEBUG
-!if $(TOOL_CHAIN_TAG) != "XCODE5"
+!if $(TOOL_CHAIN_TAG) != "XCODE5" && $(TOOL_CHAIN_TAG) != "CLANG9PE"
   GCC:*_*_*_CC_FLAGS                   = -mno-mmx -mno-sse
 !endif
 !ifdef $(SOURCE_DEBUG_ENABLE)
@@ -85,12 +85,14 @@
 [BuildOptions.common.EDKII.DXE_RUNTIME_DRIVER]
   GCC:*_*_*_DLINK_FLAGS = -z common-page-size=0x1000
   XCODE:*_*_*_DLINK_FLAGS =
+  CLANGPE: *_*_*_DLINK_FLAGS = /ALIGN:4096
 
 # Force PE/COFF sections to be aligned at 4KB boundaries to support page level
 # protection of DXE_SMM_DRIVER/SMM_CORE modules
 [BuildOptions.common.EDKII.DXE_SMM_DRIVER, BuildOptions.common.EDKII.SMM_CORE]
   GCC:*_*_*_DLINK_FLAGS = -z common-page-size=0x1000
   XCODE:*_*_*_DLINK_FLAGS =
+  CLANGPE: *_*_*_DLINK_FLAGS = /ALIGN:4096
 
 ################################################################################
 #
diff --git a/OvmfPkg/OvmfPkgIa32X64.fdf b/OvmfPkg/OvmfPkgIa32X64.fdf
index 74407072563b..28c812388213 100644
--- a/OvmfPkg/OvmfPkgIa32X64.fdf
+++ b/OvmfPkg/OvmfPkgIa32X64.fdf
@@ -279,7 +279,7 @@ INF  MdeModulePkg/Universal/Acpi/BootGraphicsResourceTableDxe/BootGraphicsResour
 INF  FatPkg/EnhancedFatDxe/Fat.inf
 INF  MdeModulePkg/Universal/Disk/UdfDxe/UdfDxe.inf
 
-!if $(TOOL_CHAIN_TAG) != "XCODE5"
+!if $(TOOL_CHAIN_TAG) != "XCODE5" && $(TOOL_CHAIN_TAG) != "CLANG9PE"
 INF  ShellPkg/DynamicCommand/TftpDynamicCommand/TftpDynamicCommand.inf
 !endif
 INF  ShellPkg/Application/Shell/Shell.inf
diff --git a/OvmfPkg/OvmfPkgX64.dsc b/OvmfPkg/OvmfPkgX64.dsc
index ba7a75884490..c9d663aa8135 100644
--- a/OvmfPkg/OvmfPkgX64.dsc
+++ b/OvmfPkg/OvmfPkgX64.dsc
@@ -66,7 +66,7 @@
   GCC:RELEASE_*_*_CC_FLAGS             = -DMDEPKG_NDEBUG
   INTEL:RELEASE_*_*_CC_FLAGS           = /D MDEPKG_NDEBUG
   MSFT:RELEASE_*_*_CC_FLAGS            = /D MDEPKG_NDEBUG
-!if $(TOOL_CHAIN_TAG) != "XCODE5"
+!if $(TOOL_CHAIN_TAG) != "XCODE5" && $(TOOL_CHAIN_TAG) != "CLANG9PE"
   GCC:*_*_*_CC_FLAGS                   = -mno-mmx -mno-sse
 !endif
 !ifdef $(SOURCE_DEBUG_ENABLE)
@@ -85,12 +85,14 @@
 [BuildOptions.common.EDKII.DXE_RUNTIME_DRIVER]
   GCC:*_*_*_DLINK_FLAGS = -z common-page-size=0x1000
   XCODE:*_*_*_DLINK_FLAGS =
+  CLANGPE: *_*_*_DLINK_FLAGS = /ALIGN:4096
 
 # Force PE/COFF sections to be aligned at 4KB boundaries to support page level
 # protection of DXE_SMM_DRIVER/SMM_CORE modules
 [BuildOptions.common.EDKII.DXE_SMM_DRIVER, BuildOptions.common.EDKII.SMM_CORE]
   GCC:*_*_*_DLINK_FLAGS = -z common-page-size=0x1000
   XCODE:*_*_*_DLINK_FLAGS =
+  CLANGPE: *_*_*_DLINK_FLAGS = /ALIGN:4096
 
 ################################################################################
 #
@@ -815,7 +817,7 @@
   OvmfPkg/Csm/Csm16/Csm16.inf
 !endif
 
-!if $(TOOL_CHAIN_TAG) != "XCODE5"
+!if $(TOOL_CHAIN_TAG) != "XCODE5" && $(TOOL_CHAIN_TAG) != "CLANG9PE"
   ShellPkg/DynamicCommand/TftpDynamicCommand/TftpDynamicCommand.inf {
     <PcdsFixedAtBuild>
       gEfiShellPkgTokenSpaceGuid.PcdShellLibAutoInitialize|FALSE
diff --git a/OvmfPkg/OvmfPkgX64.fdf b/OvmfPkg/OvmfPkgX64.fdf
index 74407072563b..28c812388213 100644
--- a/OvmfPkg/OvmfPkgX64.fdf
+++ b/OvmfPkg/OvmfPkgX64.fdf
@@ -279,7 +279,7 @@ INF  MdeModulePkg/Universal/Acpi/BootGraphicsResourceTableDxe/BootGraphicsResour
 INF  FatPkg/EnhancedFatDxe/Fat.inf
 INF  MdeModulePkg/Universal/Disk/UdfDxe/UdfDxe.inf
 
-!if $(TOOL_CHAIN_TAG) != "XCODE5"
+!if $(TOOL_CHAIN_TAG) != "XCODE5" && $(TOOL_CHAIN_TAG) != "CLANG9PE"
 INF  ShellPkg/DynamicCommand/TftpDynamicCommand/TftpDynamicCommand.inf
 !endif
 INF  ShellPkg/Application/Shell/Shell.inf
diff --git a/OvmfPkg/Sec/SecMain.inf b/OvmfPkg/Sec/SecMain.inf
index 63ba4cb555fb..b6668e3e6b92 100644
--- a/OvmfPkg/Sec/SecMain.inf
+++ b/OvmfPkg/Sec/SecMain.inf
@@ -69,3 +69,6 @@
 
 [FeaturePcd]
   gUefiOvmfPkgTokenSpaceGuid.PcdSmmSmramRequire
+
+[BuildOptions]
+  CLANGPE:*_*_*_CC_FLAGS                   =-fno-omit-frame-pointer
\ No newline at end of file
diff --git a/Readme.md b/Readme.md
index 27e4ce07719b..c75b1e4a5695 100644
--- a/Readme.md
+++ b/Readme.md
@@ -1,181 +1,39 @@
-# EDK II Project
-
-A modern, feature-rich, cross-platform firmware development environment
-for the UEFI and PI specifications from www.uefi.org.
-
-The majority of the content in the EDK II open source project uses a
-[BSD-2-Clause Plus Patent License](License.txt).  The EDK II open source project
-contains the following components that are covered by additional licenses:
-* [BaseTools/Source/C/BrotliCompress](BaseTools/Source/C/BrotliCompress/LICENSE)
-* [MdeModulePkg/Library/BrotliCustomDecompressLib](MdeModulePkg/Library/BrotliCustomDecompressLib/LICENSE)
-* [BaseTools/Source/C/LzmaCompress](BaseTools/Source/C/LzmaCompress/LZMA-SDK-README.txt)
-* [MdeModulePkg/Library/LzmaCustomDecompressLib](MdeModulePkg/Library/LzmaCustomDecompressLib/LZMA-SDK-README.txt)
-* [IntelFrameworkModulePkg/Library/LzmaCustomDecompressLib/Sdk](IntelFrameworkModulePkg/Library/LzmaCustomDecompressLib/LZMA-SDK-README.txt)
-* [BaseTools/Source/C/VfrCompile/Pccts](BaseTools/Source/C/VfrCompile/Pccts/RIGHTS)
-* [MdeModulePkg/Universal/RegularExpressionDxe/Oniguruma](MdeModulePkg/Universal/RegularExpressionDxe/Oniguruma/README)
-* [OvmfPkg](OvmfPkg/License.txt)
-* [CryptoPkg/Library/OpensslLib/openssl](https://github.com/openssl/openssl/blob/50eaac9f3337667259de725451f201e784599687/LICENSE)
-* [ArmPkg/Library/ArmSoftFloatLib/berkeley-softfloat-3](https://github.com/ucb-bar/berkeley-softfloat-3/blob/b64af41c3276f97f0e181920400ee056b9c88037/COPYING.txt)
-
-The EDK II Project is composed of packages.  The maintainers for each package
-are listed in [Maintainers.txt](Maintainers.txt).
-
-# Resources
-* [TianoCore](http://www.tianocore.org)
-* [EDK II](https://github.com/tianocore/tianocore.github.io/wiki/EDK-II)
-* [Getting Started with EDK II](https://github.com/tianocore/tianocore.github.io/wiki/Getting-Started-with-EDK-II)
-* [Mailing Lists](https://github.com/tianocore/tianocore.github.io/wiki/Mailing-Lists)
-* [TianoCore Bugzilla](https://bugzilla.tianocore.org)
-* [How To Contribute](https://github.com/tianocore/tianocore.github.io/wiki/How-To-Contribute)
-* [Release Planning](https://github.com/tianocore/tianocore.github.io/wiki/EDK-II-Release-Planning)
-
-# Code Contributions
-To make a contribution to a TianoCore project, follow these steps.
-1. Create a change description in the format specified below to
-   use in the source control commit log.
-2. Your commit message must include your `Signed-off-by` signature
-3. Submit your code to the TianoCore project using the process
-   that the project documents on its web page.  If the process is
-   not documented, then submit the code on development email list
-   for the project.
-4. It is preferred that contributions are submitted using the same
-   copyright license as the base project. When that is not possible,
-   then contributions using the following licenses can be accepted:
-   * BSD (2-clause): http://opensource.org/licenses/BSD-2-Clause
-   * BSD (3-clause): http://opensource.org/licenses/BSD-3-Clause
-   * MIT: http://opensource.org/licenses/MIT
-   * Python-2.0: http://opensource.org/licenses/Python-2.0
-   * Zlib: http://opensource.org/licenses/Zlib
-
-   For documentation:
-   * FreeBSD Documentation License
-     https://www.freebsd.org/copyright/freebsd-doc-license.html
-
-   Contributions of code put into the public domain can also be
-   accepted.
-
-   Contributions using other licenses might be accepted, but further
-   review will be required.
-
-# Developer Certificate of Origin
-
-Your change description should use the standard format for a
-commit message, and must include your `Signed-off-by` signature.
-
-In order to keep track of who did what, all patches contributed must
-include a statement that to the best of the contributor's knowledge
-they have the right to contribute it under the specified license.
-
-The test for this is as specified in the [Developer's Certificate of
-Origin (DCO) 1.1](https://developercertificate.org/). The contributor
-certifies compliance by adding a line saying
-
-  Signed-off-by: Developer Name <developer@example.org>
-
-where `Developer Name` is the contributor's real name, and the email
-address is one the developer is reachable through at the time of
-contributing.
-
-```
-Developer's Certificate of Origin 1.1
-
-By making a contribution to this project, I certify that:
-
-(a) The contribution was created in whole or in part by me and I
-    have the right to submit it under the open source license
-    indicated in the file; or
-
-(b) The contribution is based upon previous work that, to the best
-    of my knowledge, is covered under an appropriate open source
-    license and I have the right under that license to submit that
-    work with modifications, whether created in whole or in part
-    by me, under the same open source license (unless I am
-    permitted to submit under a different license), as indicated
-    in the file; or
-
-(c) The contribution was provided directly to me by some other
-    person who certified (a), (b) or (c) and I have not modified
-    it.
-
-(d) I understand and agree that this project and the contribution
-    are public and that a record of the contribution (including all
-    personal information I submit with it, including my sign-off) is
-    maintained indefinitely and may be redistributed consistent with
-    this project or the open source license(s) involved.
-```
-
-# Sample Change Description / Commit Message
-
-```
-From: Contributor Name <contributor@example.com>
-Subject: [Repository/Branch PATCH] Pkg-Module: Brief-single-line-summary
-
-Full-commit-message
-
-Signed-off-by: Contributor Name <contributor@example.com>
-```
-
-## Notes for sample patch email
-
-* The first line of commit message is taken from the email's subject
-  line following `[Repository/Branch PATCH]`. The remaining portion of the
-  commit message is the email's content.
-* `git format-patch` is one way to create this format
-
-## Definitions for sample patch email
-
-* `Repository` is the identifier of the repository the patch applies.
-  This identifier should only be provided for repositories other than
-  `edk2`. For example `edk2-BuildSpecification` or `staging`.
-* `Branch` is the identifier of the branch the patch applies. This
-  identifier should only be provided for branches other than `edk2/master`.
-  For example `edk2/UDK2015`, `edk2-BuildSpecification/release/1.27`, or
-  `staging/edk2-test`.
-* `Module` is a short identifier for the affected code or documentation. For
-  example `MdePkg`, `MdeModulePkg/UsbBusDxe`, `Introduction`, or
-  `EDK II INF File Format`.
-* `Brief-single-line-summary` is a short summary of the change.
-* The entire first line should be less than ~70 characters.
-* `Full-commit-message` a verbose multiple line comment describing
-  the change.  Each line should be less than ~70 characters.
-* `Signed-off-by` is the contributor's signature identifying them
-  by their real/legal name and their email address.
-
-# Submodules
-
-Submodule in EDK II is allowed but submodule chain should be avoided
-as possible as we can. Currently EDK II contains two submodules
-
-- CryptoPkg/Library/OpensslLib/openssl
-- ArmPkg/Library/ArmSoftFloatLib/berkeley-softfloat-3
-
-The latter one is actually required by previous one. It's inevitable
-in openssl-1.1.1 (since stable201905) for floating point parameter
-conversion, but should be dropped once there's no such need in future
-release of openssl.
-
-To get a full, buildable EDK II repository, use following steps of git
-command
-
-```
-$ git clone https://github.com/tianocore/edk2.git
-$ cd edk2
-$ git submodule update --init
-$ cd ..
-```
-
-If there's update for submodules, use following git commands to get the
-latest submodules code.
-
-```
-$ cd edk2
-$ git pull
-$ git submodule update
-```
-
-Note: When cloning submodule repos, '--recursive' option is not
-recommended. EDK II itself will not use any code/feature from
-submodules in above submodules. So using '--recursive' adds a
-dependency on being able to reach servers we do not actually want
-any code from, as well as needlessly downloading code we will not
-use.
+## New CLANG9PE tool chain
+
+CLANG9PE tool chain is added to directly generate PE/COFF image (EFI image).
+This tool chain uses LLVM Clang compiler and lld linker, generates PE/COFF
+image and PDB compatible debug symbol format. Now, it supports IA32/X64 Archs.
+It must use LLVM 9 or above release. LLVM 9 will be released soon.
+Now, LLVM 9.0.0-rc3 is ready on https://prereleases.llvm.org/9.0.0/#rc3.
+
+CLANG9PE is the cross OS tool chain. It can work on Windows/Linux/Mac. 
+For the same source code, with the same version LLVM tool chain, 
+CLANG9PE can generate the same binary image. So, the developer can 
+choose the different development environment and work on the same 
+code base. 
+
+LLVM tool chain provides the compiler and linker. To build EDK2 project, 
+some other tools are still required. On Windows OS, nmake and Visual Studio 
+are required to trig Makefile and compile BaseTools C tools. 
+On Linux/Mac, binutils and gcc are required to be installed for make and 
+compile BaseTools C tools. Because VS or GCC are mainly used to compile 
+BaseTools and provide nmake/make tool, they can keep on the stable version 
+without update.
+
+To build source code, CLANG9PE tool chain (-t CLANG9PE) can be specified
+on Windows OS, set CLANG_HOST_BIN=n, set CLANG9PE_BIN=LLVM installed directory
+CLANG_HOST_BIN is used CLANG_HOST_PREFIX. Prefix n is for nmake.
+For example:
+*  set CLANG_HOST_BIN=n
+*  set CLANG9PE_BIN=C:\Program Files\LLVM\bin\
+*  set IASL_PREFIX=C:\Asl\
+
+On Linux/Mac, export CLANG9PE_BIN=LLVM installed directory, CLANG_HOST_BIN is 
+not required, because there is no prefix for make.
+For example:
+*  export CLANG9PE_BIN=/home/clang9/bin/
+
+Now, CLANG9PE tool chain has been verified in Edk2 packages and Ovmf/Emulator
+with LLVM 9.0.0-rc3 on Windows and Linux OS. 
+OVMF IA32/X64/IA32X64 all boots to Shell on Windows and Linux OS. 
+Emulator can boot to Shell on Windows only with CLANG9PE.