llext: add support for SLID-based linking

This commit introduces support for an alternate linking method in the LLEXT subsystem, called "SLID" (short for Symbol Link Identifier), enabled by the CONFIG_LLEXT_EXPORT_BUILTINS_BY_SLID Kconfig option. SLID-based linking uses a unique identifier (integer) to identify exported symbols, instead of using the symbol name as done currently. This approach provides several benefits: * linking is faster because the comparison operation to determine whether we found the correct symbol in the export table is now an integer compare, instead of a string compare * binary size is reduced as symbol names can be dropped from the binary * confidentiality is improved as a side-effect, as symbol names are no longer present in the binary Signed-off-by: Mathieu Choplain <[email protected]>
savoirfairelinux · Jun 3, 2024 · 8aa6ae4 · 8aa6ae4
1 parent 05ad256
commit 8aa6ae4
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Showing 45 changed files with 981 additions and 7 deletions.
diff --git a/CMakeLists.txt b/CMakeLists.txt
@@ -1888,6 +1888,21 @@ if(CONFIG_BUILD_OUTPUT_INFO_HEADER)
     )
 endif()
 
+if (CONFIG_LLEXT AND CONFIG_LLEXT_EXPORT_BUILTINS_BY_SLID)
+  #slidgen must be the first post-build command to be executed
+  #on the Zephyr ELF to ensure that all other commands, such as
+  #binary file generation, are operating on a preparated ELF.
+  list(PREPEND
+    post_build_commands
+    COMMAND ${PYTHON_EXECUTABLE}
+    ${ZEPHYR_BASE}/scripts/build/llext_prepare_exptab.py
+    --elf-file ${PROJECT_BINARY_DIR}/${KERNEL_ELF_NAME}
+    --slid-listing ${PROJECT_BINARY_DIR}/slid_listing.txt
+    -vvv
+  )
+
+endif()
+
 if(NOT CMAKE_C_COMPILER_ID STREQUAL "ARMClang")
   set(check_init_priorities_input
       $<IF:$<TARGET_EXISTS:native_runner_executable>,${BYPRODUCT_KERNEL_EXE_NAME},${BYPRODUCT_KERNEL_ELF_NAME}>

diff --git a/boards/qemu/x86/qemu_x86_tiny.ld b/boards/qemu/x86/qemu_x86_tiny.ld
@@ -254,6 +254,10 @@ SECTIONS
 
 #include <zephyr/linker/rel-sections.ld>
 
+#ifdef CONFIG_LLEXT
+#include <zephyr/linker/llext-sections.ld>
+#endif
+
     /DISCARD/ :
 	{
 	*(.plt)

diff --git a/cmake/llext-edk.cmake b/cmake/llext-edk.cmake
@@ -31,6 +31,11 @@
 
 cmake_minimum_required(VERSION 3.20.0)
 
+if (CONFIG_LLEXT_EXPORT_BUILTINS_BY_SLID)
+  message(FATAL_ERROR
+    "The LLEXT EDK is not compatible with CONFIG_LLEXT_EXPORT_BUILTINS_BY_SLID.")
+endif()
+
 set(llext_edk ${PROJECT_BINARY_DIR}/${llext_edk_name})
 set(llext_edk_inc ${llext_edk}/include)
 

diff --git a/cmake/modules/extensions.cmake b/cmake/modules/extensions.cmake
@@ -5431,13 +5431,31 @@ function(add_llext_target target_name)
     COMMAND_EXPAND_LISTS
   )
 
+  # LLEXT ELF processing for importing via SLID
+  #
+  # This command must be executed as last step of the packaging process,
+  # to ensure that the ELF processed for binary generation contains SLIDs.
+  # If executed too early, it is possible that some tools executed to modify
+  # the ELF file (e.g., strip) undo the work performed here.
+  if (CONFIG_LLEXT_EXPORT_BUILTINS_BY_SLID)
+    set(slid_inject_cmd
+      ${PYTHON_EXECUTABLE}
+      ${ZEPHYR_BASE}/scripts/build/llext_inject_slids.py
+      --elf-file ${llext_pkg_output}
+      -vvv
+    )
+  else()
+    set(slid_inject_cmd ${CMAKE_COMMAND} -E true)
+  endif()
+
   # Type-specific packaging of the built binary file into an .llext file
   if(CONFIG_LLEXT_TYPE_ELF_OBJECT)
 
     # No packaging required, simply copy the object file
     add_custom_command(
       OUTPUT ${llext_pkg_output}
       COMMAND ${CMAKE_COMMAND} -E copy ${llext_pkg_input} ${llext_pkg_output}
+      COMMAND ${slid_inject_cmd}
       DEPENDS ${llext_proc_target} ${llext_pkg_input}
     )
 
@@ -5453,6 +5471,7 @@ function(add_llext_target target_name)
               $<TARGET_PROPERTY:bintools,elfconvert_flag_infile>${llext_pkg_input}
               $<TARGET_PROPERTY:bintools,elfconvert_flag_outfile>${llext_pkg_output}
               $<TARGET_PROPERTY:bintools,elfconvert_flag_final>
+      COMMAND ${slid_inject_cmd}
       DEPENDS ${llext_proc_target} ${llext_pkg_input}
     )
 
@@ -5467,6 +5486,7 @@ function(add_llext_target target_name)
               $<TARGET_PROPERTY:bintools,strip_flag_infile>${llext_pkg_input}
               $<TARGET_PROPERTY:bintools,strip_flag_outfile>${llext_pkg_output}
               $<TARGET_PROPERTY:bintools,strip_flag_final>
+      COMMAND ${slid_inject_cmd}
       DEPENDS ${llext_proc_target} ${llext_pkg_input}
     )
 

diff --git a/include/zephyr/arch/arc/v2/linker.ld b/include/zephyr/arch/arc/v2/linker.ld
@@ -81,6 +81,10 @@ SECTIONS {
 
 #include <zephyr/linker/rel-sections.ld>
 
+#ifdef CONFIG_LLEXT
+#include <zephyr/linker/llext-sections.ld>
+#endif
+
 	GROUP_START(ROMABLE_REGION)
 
 	SECTION_PROLOGUE(_TEXT_SECTION_NAME,,ALIGN(1024)) {

diff --git a/include/zephyr/arch/arm/cortex_a_r/scripts/linker.ld b/include/zephyr/arch/arm/cortex_a_r/scripts/linker.ld
@@ -98,6 +98,10 @@ SECTIONS
 {
 #include <zephyr/linker/rel-sections.ld>
 
+#ifdef CONFIG_LLEXT
+#include <zephyr/linker/llext-sections.ld>
+#endif
+
     /*
      * .plt and .iplt are here according to 'arm-zephyr-elf-ld --verbose',
      * before text section.

diff --git a/include/zephyr/arch/arm/cortex_m/scripts/linker.ld b/include/zephyr/arch/arm/cortex_m/scripts/linker.ld
@@ -113,6 +113,10 @@ SECTIONS
 
 #include <zephyr/linker/rel-sections.ld>
 
+#ifdef CONFIG_LLEXT
+#include <zephyr/linker/llext-sections.ld>
+#endif
+
     /*
      * .plt and .iplt are here according to 'arm-zephyr-elf-ld --verbose',
      * before text section.

diff --git a/include/zephyr/arch/arm64/scripts/linker.ld b/include/zephyr/arch/arm64/scripts/linker.ld
@@ -77,6 +77,10 @@ SECTIONS
 
 #include <zephyr/linker/rel-sections.ld>
 
+#ifdef CONFIG_LLEXT
+#include <zephyr/linker/llext-sections.ld>
+#endif
+
     /*
      * .plt and .iplt are here according to 'arm-zephyr-elf-ld --verbose',
      * before text section.

diff --git a/include/zephyr/arch/mips/linker.ld b/include/zephyr/arch/mips/linker.ld
@@ -46,6 +46,10 @@ SECTIONS
 
 #include <zephyr/linker/rel-sections.ld>
 
+#ifdef CONFIG_LLEXT
+#include <zephyr/linker/llext-sections.ld>
+#endif
+
     SECTION_PROLOGUE(_VECTOR_SECTION_NAME,,)
     {
 		. = ALIGN(0x1000);

diff --git a/include/zephyr/arch/nios2/linker.ld b/include/zephyr/arch/nios2/linker.ld
@@ -85,6 +85,10 @@ SECTIONS
 
 #include <zephyr/linker/rel-sections.ld>
 
+#ifdef CONFIG_LLEXT
+#include <zephyr/linker/llext-sections.ld>
+#endif
+
     /*
      * .plt and .iplt are here according to
      * 'nios2-zephyr-elf-ld --verbose', before text section.

diff --git a/include/zephyr/arch/posix/linker.ld b/include/zephyr/arch/posix/linker.ld
@@ -21,6 +21,10 @@
 SECTIONS
  {
 
+#ifdef CONFIG_LLEXT
+#include <zephyr/linker/llext-sections.ld>
+#endif
+
 SECTION_PROLOGUE(rom_start,,)
 {
 	/* Located in generated directory. This file is populated by the

diff --git a/include/zephyr/arch/riscv/common/linker.ld b/include/zephyr/arch/riscv/common/linker.ld
@@ -122,6 +122,10 @@ SECTIONS
 
 #include <zephyr/linker/rel-sections.ld>
 
+#ifdef CONFIG_LLEXT
+#include <zephyr/linker/llext-sections.ld>
+#endif
+
     /*
      * The .plt and .iplt are here according to
      * 'riscv32-zephyr-elf-ld --verbose', before text section.

diff --git a/include/zephyr/arch/sparc/linker.ld b/include/zephyr/arch/sparc/linker.ld
@@ -23,6 +23,10 @@ SECTIONS
 
 #include <zephyr/linker/rel-sections.ld>
 
+#ifdef CONFIG_LLEXT
+#include <zephyr/linker/llext-sections.ld>
+#endif
+
     __rom_region_start = .;
 
     SECTION_PROLOGUE(_TEXT_SECTION_NAME,,)

diff --git a/include/zephyr/arch/x86/ia32/linker.ld b/include/zephyr/arch/x86/ia32/linker.ld
@@ -77,6 +77,10 @@ SECTIONS
 
 #include <zephyr/linker/rel-sections.ld>
 
+#ifdef CONFIG_LLEXT
+#include <zephyr/linker/llext-sections.ld>
+#endif
+
     /DISCARD/ :
 	{
 	*(.plt)

diff --git a/include/zephyr/arch/x86/intel64/linker.ld b/include/zephyr/arch/x86/intel64/linker.ld
@@ -236,4 +236,7 @@ SECTIONS
 	.shstrtab 0 : { *(.shstrtab) }
 #endif
 
+#ifdef CONFIG_LLEXT
+	#include <zephyr/linker/llext-sections.ld>
+#endif
 }
diff --git a/include/zephyr/linker/llext-sections.ld b/include/zephyr/linker/llext-sections.ld
@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: Apache-2.0 */
+
+	/*
+	 * Special section used by LLEXT if CONFIG_LLEXT_EXPORT_BUILTINS_BY_SLID
+	 * is enabled. Declare this section to prevent it from being considered orphan.
+	 *
+	 * This section is used to temporarily save the exported symbols' names in the
+	 * Zephyr ELF for post-processing, but it is not included in the final binary.
+	 *
+	 * NOTE: This section MUST start at address 0, as the post-processing scripts
+	 * assume that the address of any data in this section (i.e., symbol names) is
+	 * strictly equivalent to the offset inside the section.
+	 */
+#ifdef CONFIG_LLEXT_EXPORT_BUILTINS_BY_SLID
+	SECTION_PROLOGUE(llext_exports_strtab, 0 (COPY), )
+	{
+	  KEEP(*(llext_exports_strtab))
+	}
+#endif
diff --git a/include/zephyr/llext/symbol.h b/include/zephyr/llext/symbol.h
@@ -10,6 +10,7 @@
 #include <zephyr/sys/iterable_sections.h>
 #include <zephyr/toolchain.h>
 #include <stddef.h>
+#include <stdint.h>
 
 #ifdef __cplusplus
 extern "C" {
@@ -27,14 +28,27 @@ extern "C" {
  * Symbols may be named function or global objects that have been exported
  * for linking. These constant symbols are useful in the base image
  * as they may be placed in ROM.
+ *
+ * @note When updating this structure, make sure to also update the
+ * 'scripts/build/llext_prepare_exptab.py' build script.
  */
 struct llext_const_symbol {
-	/** Name of symbol */
-	const char *const name;
+	/** At build time, we always write to 'name'.
+	 *  At runtime, which field is used depends
+	 *  on CONFIG_LLEXT_EXPORT_BUILTINS_BY_SLID.
+	 */
+	union {
+		/** Name of symbol */
+		const char *const name;
+
+		/** Symbol Link Identifier */
+		const uintptr_t slid;
+	};
 
 	/** Address of symbol */
 	const void *const addr;
 };
+BUILD_ASSERT(sizeof(struct llext_const_symbol) == 2 * sizeof(uintptr_t));
 
 /**
  * @brief Symbols are named memory addresses
@@ -75,10 +89,19 @@ struct llext_symtable {
  *
  * @param x Symbol to export to extensions
  */
+#ifdef CONFIG_LLEXT_EXPORT_BUILTINS_BY_SLID
+#define EXPORT_SYMBOL(x)							\
+	static const char Z_GENERIC_SECTION("llext_exports_strtab") __used	\
+		x ## _sym_name[] = STRINGIFY(x);				\
+	static const STRUCT_SECTION_ITERABLE(llext_const_symbol, x ## _sym) = {	\
+		.name = x ## _sym_name, .addr = (const void *)&x,			\
+	}
+#else
 #define EXPORT_SYMBOL(x)							\
 	static const STRUCT_SECTION_ITERABLE(llext_const_symbol, x ## _sym) = {	\
 		.name = STRINGIFY(x), .addr = (const void *)&x,			\
 	}
+#endif
 
 /**
  * @brief Exports a symbol from an extension to the base image