pico-sdk: Switch to picolibc

This selects picolibc by using --specs=picolibc.specs for compiling
and linking. The linker scripts are adjusted to add KEEP to ensure
that --gc-sections doesn't remove the contents of the files.

Signed-off-by: Keith Packard <[email protected]>

Author: keith-packard

src/rp2040/boot_stage2/CMakeLists.txt

@@ -43,15 +43,16 @@ function(pico_define_boot_stage2 NAME SOURCES)
     if (PICO_C_COMPILER_IS_CLANG)
         target_link_options(${NAME} PRIVATE "-nostdlib")
     elseif (PICO_C_COMPILER_IS_GNU)
-        target_link_options(${NAME} PRIVATE "--specs=nosys.specs")
+        target_compile_options(${NAME} PRIVATE "--specs=picolibc.specs")
+        target_link_options(${NAME} PRIVATE "--specs=picolibc.specs")
         target_link_options(${NAME} PRIVATE "-nostartfiles")
     endif ()
 
     # boot2_helpers include dir
     target_include_directories(${NAME} PRIVATE ${PICO_BOOT_STAGE2_DIR}/asminclude)
 
     target_link_libraries(${NAME} hardware_regs boot_stage2_headers)
-    target_link_options(${NAME} PRIVATE "LINKER:--script=${PICO_BOOT_STAGE2_DIR}/boot_stage2.ld")
+    target_link_options(${NAME} PRIVATE "-T${PICO_BOOT_STAGE2_DIR}/boot_stage2.ld")
     set_target_properties(${NAME} PROPERTIES LINK_DEPENDS ${PICO_BOOT_STAGE2_DIR}/boot_stage2.ld)
 
     pico_add_dis_output(${NAME})

src/rp2040/boot_stage2/boot_stage2.ld

@@ -8,7 +8,7 @@ SECTIONS {
     . = ORIGIN(SRAM);
     .text : {
         _start = .; /* make LLVM happy */
-        *(.entry)
-        *(.text)
+        KEEP(*(.entry))
+        KEEP(*(.text .text.*))
     } >SRAM
 }

src/rp2350/boot_stage2/CMakeLists.txt

@@ -43,15 +43,15 @@ function(pico_define_boot_stage2 NAME SOURCES)
     if (PICO_C_COMPILER_IS_CLANG)
         target_link_options(${NAME} PRIVATE "-nostdlib")
     elseif (PICO_C_COMPILER_IS_GNU)
-        target_link_options(${NAME} PRIVATE "--specs=nosys.specs")
+        target_link_options(${NAME} PRIVATE "--specs=picolibc.specs")
         target_link_options(${NAME} PRIVATE "-nostartfiles")
     endif ()
 
     # boot2_helpers include dir
     target_include_directories(${NAME} PRIVATE ${PICO_BOOT_STAGE2_DIR}/asminclude)
 
     target_link_libraries(${NAME} hardware_regs boot_stage2_headers)
-    target_link_options(${NAME} PRIVATE "LINKER:--script=${PICO_BOOT_STAGE2_DIR}/boot_stage2.ld")
+    target_link_options(${NAME} PRIVATE "-T${PICO_BOOT_STAGE2_DIR}/boot_stage2.ld")
     set_target_properties(${NAME} PROPERTIES LINK_DEPENDS ${PICO_BOOT_STAGE2_DIR}/boot_stage2.ld)
 
     pico_add_dis_output(${NAME})

src/rp2350/boot_stage2/boot_stage2.ld

@@ -8,7 +8,7 @@ SECTIONS {
     . = ORIGIN(SRAM);
     .text : {
         _start = .; /* make LLVM happy */
-        *(.entry)
-        *(.text)
+        KEEP(*(.entry .entry.*))
+        KEEP(*(.text .text.*))
     } >SRAM
 }

src/rp2_common/pico_runtime/CMakeLists.txt

@@ -46,7 +46,8 @@ endforeach()
 
 # todo is this correct/needed?
 if (PICO_C_COMPILER_IS_GNU)
-    target_link_options(pico_runtime INTERFACE "--specs=nosys.specs")
+    target_compile_options(pico_runtime INTERFACE "--specs=picolibc.specs")
+    target_link_options(pico_runtime INTERFACE "--specs=picolibc.specs")
 elseif (PICO_C_COMPILER_IS_CLANG)
    # target_link_options(pico_runtime INTERFACE "-nostdlib")
 endif()
@@ -144,4 +145,4 @@ function(pico_minimize_runtime TARGET)
     if (NOT RUNTIME_INCLUDE_FPGA_CHECK)
         target_compile_definitions(${TARGET} PRIVATE PICO_NO_FPGA_CHECK=1)
     endif()
-endfunction()
+endfunction()

src/rp2_common/pico_standard_link/CMakeLists.txt

@@ -65,7 +65,7 @@ if (NOT TARGET pico_standard_link)
     # if PICO_TARGET_BINARY_TYPE is set to foo on the target, otherwise ${CMAKE_CURRENT_LIST_DIR}/memmap_${PICO_DEFAULT_BINARY_TYPE).ld
     set(_LINKER_SCRIPT_EXPRESSION "$<IF:$<BOOL:$<TARGET_PROPERTY:PICO_TARGET_LINKER_SCRIPT>>,$<TARGET_PROPERTY:PICO_TARGET_LINKER_SCRIPT>,${PICO_LINKER_SCRIPT_PATH}/memmap_$<IF:$<STREQUAL:$<TARGET_PROPERTY:PICO_TARGET_BINARY_TYPE>,>,${PICO_DEFAULT_BINARY_TYPE},$<TARGET_PROPERTY:PICO_TARGET_BINARY_TYPE>>.ld>")
     target_link_options(pico_standard_link INTERFACE
-        "LINKER:--script=${_LINKER_SCRIPT_EXPRESSION}"
+        "-T${_LINKER_SCRIPT_EXPRESSION}"
             )
     pico_add_link_depend(pico_standard_link ${_LINKER_SCRIPT_EXPRESSION})
     unset(_LINKER_SCRIPT_EXPRESSION)