nrfconnect · carlescufi · Nov 25, 2025 · Nov 25, 2025 · Dec 3, 2025
diff --git a/CMakeLists.txt b/CMakeLists.txt
@@ -311,8 +311,13 @@
 toolchain_linker_add_compiler_options(${simple_options})
 
 if(CONFIG_LTO)
-  zephyr_compile_options($<TARGET_PROPERTY:compiler,optimization_lto>)
-  add_link_options($<TARGET_PROPERTY:linker,lto_arguments>)
+  if(CONFIG_LTO_SINGLE_THREADED)
+    zephyr_compile_options($<TARGET_PROPERTY:compiler,optimization_lto_st>)
+    add_link_options($<TARGET_PROPERTY:linker,lto_arguments_st>)
+  else()
+    zephyr_compile_options($<TARGET_PROPERTY:compiler,optimization_lto>)
+    add_link_options($<TARGET_PROPERTY:linker,lto_arguments>)
+  endif()
 endif()
 
 if(CONFIG_STD_C23)
@@ -409,7 +414,7 @@
  zephyr_compile_options($<$<COMPILE_LANGUAGE:ASM>:$<TARGET_PROPERTY:compiler,freestanding>>)
 endif()

 if (CONFIG_PICOLIBC AND NOT CONFIG_PICOLIBC_IO_FLOAT)
  # @Intent: Set compiler specific flag to disable printf-related optimizations
  zephyr_compile_options($<$<COMPILE_LANGUAGE:C>:$<TARGET_PROPERTY:compiler,no_printf_return_value>>)
 endif()
@@ -1129,7 +1134,7 @@

 get_property(OUTPUT_FORMAT        GLOBAL PROPERTY PROPERTY_OUTPUT_FORMAT)

 if (CONFIG_CODE_DATA_RELOCATION)
  set(CODE_RELOCATION_DEP code_relocation_source_lib)
 endif() # CONFIG_CODE_DATA_RELOCATION

@@ -2106,7 +2111,7 @@
    )
 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.
@@ -2172,7 +2177,7 @@
 endif()

 # Generate USB-C VIF policies in XML format
 if (CONFIG_BUILD_OUTPUT_VIF)
  include(${CMAKE_CURRENT_LIST_DIR}/cmake/vif.cmake)
 endif()

@@ -2223,7 +2228,7 @@
      --build-header ${PROJECT_BINARY_DIR}/include/generated/zephyr/version.h
  )

  if (NOT CONFIG_LOG_DICTIONARY_DB_TARGET)
    # If not using a separate target for generating logging dictionary
    # database, add the generation to post build command to make sure
    # the database is actually being generated.

diff --git a/Kconfig.zephyr b/Kconfig.zephyr
@@ -529,6 +529,14 @@ config LTO
 	help
 	  This option enables Link Time Optimization.
 
+config LTO_SINGLE_THREADED
+	bool "Single-threaded LTO"
+	depends on LTO
+	help
+	  This option instructs the linker to use a single thread to process
+	  LTO. See the following issue for more info:
+	  https://github.com/zephyrproject-rtos/sdk-ng/issues/1038
+
 config COMPILER_WARNINGS_AS_ERRORS
 	bool "Treat warnings as errors"
 	help

diff --git a/cmake/compiler/compiler_flags_template.cmake b/cmake/compiler/compiler_flags_template.cmake
@@ -17,6 +17,9 @@ set_compiler_property(PROPERTY optimization_size_aggressive)
 
 set_compiler_property(PROPERTY optimization_fast)
 
+set_compiler_property(PROPERTY optimization_lto)
+set_compiler_property(PROPERTY optimization_lto_st)
+
 #######################################################
 # This section covers flags related to warning levels #
 #######################################################

diff --git a/cmake/compiler/gcc/compiler_flags.cmake b/cmake/compiler/gcc/compiler_flags.cmake
@@ -25,6 +25,7 @@
 
 if(CMAKE_C_COMPILER_VERSION GREATER_EQUAL "4.5.0")
   set_compiler_property(PROPERTY optimization_lto -flto=auto)
+  set_compiler_property(PROPERTY optimization_lto_st -flto=1)
   set_compiler_property(PROPERTY prohibit_lto -fno-lto)
 endif()
 
@@ -113,7 +114,7 @@
 # GCC compiler flags for C standard. The specific standard must be appended by user.
 set_compiler_property(PROPERTY cstd -std=)

 if (NOT CONFIG_NEWLIB_LIBC AND
    NOT (CONFIG_PICOLIBC AND NOT CONFIG_PICOLIBC_USE_MODULE) AND
    NOT COMPILER STREQUAL "xcc" AND
    NOT COMPILER STREQUAL "xt-clang" AND

diff --git a/cmake/linker/ld/linker_flags.cmake b/cmake/linker/ld/linker_flags.cmake
@@ -43,6 +43,7 @@ endif()
 set_property(TARGET linker PROPERTY partial_linking "-r")
 
 set_property(TARGET linker PROPERTY lto_arguments -flto=auto -fno-ipa-sra -ffunction-sections -fdata-sections)
+set_property(TARGET linker PROPERTY lto_arguments_st -flto=1 -fno-ipa-sra -ffunction-sections -fdata-sections)
 
 check_set_linker_property(TARGET linker PROPERTY no_relax ${LINKERFLAGPREFIX},--no-relax)
 

diff --git a/cmake/linker/linker_flags_template.cmake b/cmake/linker/linker_flags_template.cmake
@@ -50,6 +50,10 @@ set_property(TARGET linker PROPERTY no_relax)
 # Linker flag for enabling relaxation of address optimization for jump calls.
 set_property(TARGET linker PROPERTY relax)
 
+# Linker flags for Link Time Optimizations (LTO)
+set_property(TARGET linker PROPERTY lto_arguments)
+set_property(TARGET linker PROPERTY lto_arguments_st)
+
 # Linker flag for defining specs. Defined only by gcc, when gcc is used as
 # front-end for ld.
 set_compiler_property(PROPERTY specs)
diff --git a/cmake/linker/lld/linker_flags.cmake b/cmake/linker/lld/linker_flags.cmake
@@ -14,6 +14,7 @@ endif()
 set_property(TARGET linker PROPERTY no_position_independent "${LINKERFLAGPREFIX},--no-pie")
 
 set_property(TARGET linker PROPERTY lto_arguments)
+set_property(TARGET linker PROPERTY lto_arguments_st)
 
 check_set_linker_property(TARGET linker PROPERTY sort_alignment ${LINKERFLAGPREFIX},--sort-section=alignment)
 

diff --git a/dts/vendor/nordic/nrf54l_05_10_15.dtsi b/dts/vendor/nordic/nrf54l_05_10_15.dtsi
@@ -694,7 +694,7 @@
 				gpio-controller;
 				reg = <0x10a000 0x300>;
 				#gpio-cells = <2>;
-				ngpios = <5>;
+				ngpios = <7>;
 				status = "disabled";
 				port = <0>;
 				gpiote-instance = <&gpiote30>;

diff --git a/tests/kernel/common/testcase.yaml b/tests/kernel/common/testcase.yaml
@@ -89,3 +89,17 @@ tests:
     integration_platforms:
       - qemu_x86
       - mps2/an385
+  kernel.common.lto.singlethreaded:
+    platform_key:
+      - arch
+    # CONFIG_CODE_DATA_RELOCATION causes a build error (issue #69730)
+    filter: CONFIG_ISR_TABLES_LOCAL_DECLARATION_SUPPORTED and not CONFIG_CODE_DATA_RELOCATION
+    tags: lto
+    extra_configs:
+      - CONFIG_TEST_USERSPACE=n
+      - CONFIG_ISR_TABLES_LOCAL_DECLARATION=y
+      - CONFIG_LTO=y
+      - CONFIG_LTO_SINGLE_THREADED=y
+    integration_platforms:
+      - qemu_x86
+      - mps2/an385
diff --git a/tests/misc/test_build/testcase.yaml b/tests/misc/test_build/testcase.yaml
@@ -36,6 +36,15 @@ tests:
       - CONFIG_ISR_TABLES_LOCAL_DECLARATION=y
       - CONFIG_LTO=y
       - CONFIG_PICOLIBC_USE_MODULE=y
+  buildsystem.lto.st.picolibc_module:
+    build_only: true
+    platform_allow:
+      - nucleo_f746zg
+    extra_configs:
+      - CONFIG_ISR_TABLES_LOCAL_DECLARATION=y
+      - CONFIG_LTO=y
+      - CONFIG_LTO_SINGLE_THREADED=y
+      - CONFIG_PICOLIBC_USE_MODULE=y
   buildsystem.arm.null_pointer_exception_detection_dwt:
     build_only: true
     platform_allow: