LLVM: add built-in lld linker support for x86.

add support to use LLVM built-in lld linker to build
zephyr applications for x86 platforms.

Signed-off-by: Chen Peng1 <peng1.chen@intel.com>

Kconfig.zephyr

@@ -162,6 +162,13 @@ config CMAKE_LINKER_GENERATOR
 
 endchoice
 
+config LLVM_USE_LD
+	bool "LLVM use ld linker"
+	depends on "${ZEPHYR_TOOLCHAIN_VARIANT}" = "llvm"
+	default y
+	help
+	  Use binutils ld linker instead of LLVM built-in lld linker.
+
 config HAVE_CUSTOM_LINKER_SCRIPT
 	bool "Custom linker script provided"
 	help

cmake/linker/lld/target.cmake

@@ -107,7 +107,7 @@ endfunction(toolchain_ld_link_elf)
 
 
 # Load toolchain_ld-family macros
-include(${ZEPHYR_BASE}/cmake/linker/ld/target_base.cmake)
+include(${ZEPHYR_BASE}/cmake/linker/${LINKER}/target_base.cmake)
 include(${ZEPHYR_BASE}/cmake/linker/${LINKER}/target_baremetal.cmake)
 include(${ZEPHYR_BASE}/cmake/linker/ld/target_cpp.cmake)
 include(${ZEPHYR_BASE}/cmake/linker/ld/target_relocation.cmake)

cmake/linker/lld/target_baremetal.cmake

@@ -4,7 +4,7 @@
 
 macro(toolchain_ld_baremetal)
 
-  # LINKERFLAGPREFIX comes from linker/ld/target.cmake
+  # LINKERFLAGPREFIX comes from linker/lld/target.cmake
   zephyr_ld_options(
     -nostdlib
     -static
@@ -12,6 +12,13 @@ macro(toolchain_ld_baremetal)
     ${LINKERFLAGPREFIX},-N
   )
 
+  # Force LLVM to use built-in lld linker
+  if(NOT CONFIG_LLVM_USE_LD)
+    zephyr_ld_options(
+      -fuse-ld=lld
+  )
+  endif()
+
   # Funny thing is if this is set to =error, some architectures will
   # skip this flag even though the compiler flag check passes
   # (e.g. ARC and Xtensa). So warning should be the default for now.

cmake/linker/lld/target_base.cmake

@@ -0,0 +1,28 @@
+# SPDX-License-Identifier: Apache-2.0
+
+# See root CMakeLists.txt for description and expectations of these macros
+
+macro(toolchain_ld_base)
+
+  if(NOT PROPERTY_LINKER_SCRIPT_DEFINES)
+    set_property(GLOBAL PROPERTY PROPERTY_LINKER_SCRIPT_DEFINES -D__GCC_LINKER_CMD__)
+  endif()
+
+  # TOOLCHAIN_LD_FLAGS comes from compiler/clang/target.cmake
+  # LINKERFLAGPREFIX comes from linker/lld/target.cmake
+  zephyr_ld_options(
+    ${TOOLCHAIN_LD_FLAGS}
+  )
+
+  zephyr_ld_options(
+    ${LINKERFLAGPREFIX},--gc-sections
+    ${LINKERFLAGPREFIX},--build-id=none
+  )
+
+  # Sort each input section by alignment.
+  zephyr_ld_option_ifdef(
+    CONFIG_LINKER_SORT_BY_ALIGNMENT
+    ${LINKERFLAGPREFIX},--sort-section=alignment
+  )
+
+endmacro()

cmake/toolchain/llvm/generic.cmake

@@ -9,7 +9,11 @@ endif()
 set(LLVM_TOOLCHAIN_PATH ${CLANG_ROOT_DIR} CACHE PATH "clang install directory")
 
 set(COMPILER clang)
-set(LINKER lld)
+if(CONFIG_LLVM_USE_LD)
+  set(LINKER ld)
+else()
+  set(LINKER lld)
+endif()
 set(BINTOOLS llvm)
 
 if("${ARCH}" STREQUAL "arm")

include/zephyr/arch/x86/ia32/linker.ld

@@ -313,6 +313,15 @@ SECTIONS
 
 	/* Needs KEEP() as ENTRY() is given a physical address */
 	KEEP(*(.text.__start))
+/*
+ * We need these sections to extract interrupt information, but they
+ * will be removed with "--gc-sections" by LLVM lld, so add keep
+ * command to save them.
+ */
+#ifndef CONFIG_LLVM_USE_LD
+	KEEP(*(.text.irqstubs))
+	KEEP(*(".gnu.linkonce.t.exc_*_stub"))
+#endif
 	*(.text)
 	*(".text.*")
 	*(.gnu.linkonce.t.*)
@@ -532,7 +541,22 @@ SECTIONS
 #include <zephyr/linker/debug-sections.ld>
 
 	/DISCARD/ : { *(.note.GNU-stack) }
+/*
+ * eh_frame section won't be removed even with "--gc-sections" by LLVM lld.
+ */
+#if !defined(CONFIG_EXCEPTIONS)
+	/DISCARD/ : { *(.eh_frame) }
+#endif
 
+/*
+ * The sections below are still treated as warnings
+ * with "--orphan-handling=warn" by LLVM lld.
+ */
+#if !defined(CONFIG_LLVM_USE_LD)
+	.symtab 0 : { *(.symtab) }
+	.strtab 0 : { *(.strtab) }
+	.shstrtab 0 : { *(.shstrtab) }
+#endif
 	}
 
 #ifdef CONFIG_XIP

include/zephyr/arch/x86/intel64/linker.ld

@@ -217,4 +217,21 @@ SECTIONS
 	*(.rel.*)
 	*(.rela.*)
 	}
+/*
+ * eh_frame section won't be removed even with "--gc-sections" by LLVM lld.
+ */
+#if !defined(CONFIG_EXCEPTIONS)
+	/DISCARD/ : { *(.eh_frame) }
+#endif
+
+/*
+ * The sections below are still treated as warnings
+ * with "--orphan-handling=warn" by LLVM lld.
+ */
+#if !defined(CONFIG_LLVM_USE_LD)
+	.symtab 0 : { *(.symtab) }
+	.strtab 0 : { *(.strtab) }
+	.shstrtab 0 : { *(.shstrtab) }
+#endif
+
 }