Some cleanup of C++ support and fix GCC 6 builds

cmake/preload/toolchains/util/pico_arm_gcc_common.cmake

@@ -4,6 +4,9 @@
 # wrongly emit .fpu softvfp regardless of any other options! go figure!!!
 if (PICO_HARD_FLOAT_ABI)
     set(PICO_COMMON_LANG_FLAGS "${PICO_COMMON_LANG_FLAGS} -mfloat-abi=hard")
+elseif(CMAKE_SYSTEM_PROCESSOR STREQUAL cortex-m0plus)
+    # older GCC dont accept softfp for M0+ and end up picking wrong libraries in multilib
+    set(PICO_COMMON_LANG_FLAGS "${PICO_COMMON_LANG_FLAGS} -mfloat-abi=soft")
 else()
     set(PICO_COMMON_LANG_FLAGS "${PICO_COMMON_LANG_FLAGS} -mfloat-abi=softfp")
 endif()

src/BUILD.bazel

@@ -14,6 +14,7 @@ alias(
         "//src/common/hardware_claim:__pkg__",
         "//src/common/pico_base_headers:__pkg__",
         "//src/common/pico_binary_info:__pkg__",
+        "//src/rp2_common/pico_cxx_options:__pkg__",
         # These libraries sometimes need the host version even though they live
         # in rp2_common.
         "//src/rp2_common/boot_bootrom_headers:__pkg__",

src/common/pico_base_headers/BUILD.bazel

@@ -125,6 +125,7 @@ cc_library(
         "//src/rp2_common/hardware_watchdog:__pkg__",
         "//src/rp2_common/hardware_xosc:__pkg__",
         "//src/rp2_common/pico_crt0:__pkg__",
+        "//src/rp2_common/pico_cxx_options:__pkg__",
         "//src/rp2_common/pico_platform_common:__pkg__",
         "//src/rp2_common/pico_printf:__pkg__",
         "//src/rp2_common/pico_runtime:__pkg__",

src/rp2_common/pico_clib_interface/BUILD.bazel

@@ -63,11 +63,16 @@ cc_library(
 
 cc_library(
     name = "llvm_libc_interface_link",
-    srcs = ["llvm_libc_interface.c"],
+    srcs = [
+        "cxa_guard.c",
+        "llvm_libc_interface.c",
+        "llvm_libc_interface_cpp.cpp",
+    ],
     implementation_deps = [
         ":llvm_libc_interface",
         "//src/rp2_common/pico_atomic",
         "//src/rp2_common/pico_bootrom",
+        "//src/rp2_common/pico_cxx_options",
         "//src/rp2_common/pico_runtime_init",
         "//src/rp2_common/pico_stdio:pico_stdio_headers",
     ],
@@ -85,10 +90,15 @@ alias(
 
 cc_library(
     name = "newlib_interface_link",
-    srcs = ["newlib_interface.c"],
+    srcs = [
+        "cxa_guard.c",
+        "newlib_interface.c",
+    ],
     implementation_deps = [
         "//src/common/pico_time",
+        "//src/rp2_common/pico_atomic",
         "//src/rp2_common/pico_bootrom",
+        "//src/rp2_common/pico_cxx_options",
         "//src/rp2_common/pico_printf",
         "//src/rp2_common/pico_runtime_init",
         "//src/rp2_common/pico_stdio:pico_stdio_headers",
@@ -107,10 +117,15 @@ alias(
 
 cc_library(
     name = "picolibc_interface_link",
-    srcs = ["picolibc_interface.c"],
+    srcs = [
+        "cxa_guard.c",
+        "picolibc_interface.c",
+    ],
     implementation_deps = [
         "//src/common/pico_time",
+        "//src/rp2_common/pico_atomic",
         "//src/rp2_common/pico_bootrom",
+        "//src/rp2_common/pico_cxx_options",
         "//src/rp2_common/pico_printf",
         "//src/rp2_common/pico_runtime_init",
         "//src/rp2_common/pico_stdio:pico_stdio_headers",

src/rp2_common/pico_clib_interface/CMakeLists.txt

@@ -6,16 +6,20 @@ if (NOT TARGET pico_clib_interface)
 
     target_sources(pico_newlib_interface INTERFACE
             ${CMAKE_CURRENT_LIST_DIR}/newlib_interface.c
+            ${CMAKE_CURRENT_LIST_DIR}/cxa_guard.c
     )
+    pico_mirrored_target_link_libraries(pico_newlib_interface INTERFACE pico_stdio pico_atomic pico_cxx_options)
 
     # ---- picolibc ----
 
     pico_add_library(pico_picolibc_interface)
 
     target_sources(pico_picolibc_interface INTERFACE
             ${CMAKE_CURRENT_LIST_DIR}/picolibc_interface.c
+            ${CMAKE_CURRENT_LIST_DIR}/cxa_guard.c
     )
 
+    pico_mirrored_target_link_libraries(pico_picolibc_interface INTERFACE pico_stdio pico_atomic pico_cxx_options)
     # replacing the functions is fine it seems
     #target_compile_definitions(pico_picolibc_interface INTERFACE
     #            PICO_STDIO_SHORT_CIRCUIT_CLIB_FUNCS=0
@@ -26,13 +30,14 @@ if (NOT TARGET pico_clib_interface)
 
     target_sources(pico_llvm_libc_interface INTERFACE
             ${CMAKE_CURRENT_LIST_DIR}/llvm_libc_interface.c
+            ${CMAKE_CURRENT_LIST_DIR}/llvm_libc_interface_cpp.cpp
+            ${CMAKE_CURRENT_LIST_DIR}/cxa_guard.c
     )
 
     target_include_directories(pico_llvm_libc_interface SYSTEM INTERFACE
             ${CMAKE_CURRENT_LIST_DIR}/include/llvm_libc
     )
-    target_link_libraries(pico_llvm_libc_interface INTERFACE pico_atomic)
-    pico_mirrored_target_link_libraries(pico_llvm_libc_interface INTERFACE pico_stdio)
+    pico_mirrored_target_link_libraries(pico_llvm_libc_interface INTERFACE pico_stdio pico_atomic pico_cxx_options)
 
     if (NOT PICO_CLIB)
         # PICO_CMAKE_CONFIG: PICO_CLIB, The C library to use e.g. newlib/picolibc/llvm_libc, type=string, default=based on PICO_COMPILER, group=build, docref=cmake-toolchain-config

src/rp2_common/pico_clib_interface/cxa_guard.c

@@ -0,0 +1,92 @@
+/*
+* Copyright (c) 2026 Raspberry Pi (Trading) Ltd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include "pico/cxx_options.h"
+
+#define CXA_GUARD_UNINITIALIZED 0
+#define CXA_GUARD_INITIALIZED 1
+#define CXA_GUARD_INITIALIZING 2
+
+#if PICO_CXX_THREAD_SAFE_STATIC_INIT
+#include <stdatomic.h>
+#include <hardware/sync.h>
+
+// newer LLVM complains on RP2040 because there are no atomics (it doesn't know we have pico_atomic)
+Clang_Pragma("clang diagnostic push")
+Clang_Pragma("clang diagnostic ignored \"-Watomic-alignment\"")
+
+int __cxa_guard_acquire(int32_t *guard_object) {
+    // Cast the raw pointer to a standard C11 atomic pointer type
+    _Atomic int32_t *atomic_guard = (_Atomic int32_t *)guard_object;
+
+    while (true) {
+        // read current state
+        int32_t current = atomic_load_explicit(atomic_guard, memory_order_acquire);
+
+        // bit 0 set -> Initialization is complete, skip constructor
+        if (current & CXA_GUARD_INITIALIZED) {
+            return 0;
+        }
+
+        // bit 1 set -> another thread/core is initializing it, so sleep
+        if (current & CXA_GUARD_INITIALIZING) {
+            __wfe();
+            continue;
+        }
+
+        // attempt to atomically claim the lock by moving state from CXA_GUARD_UNINITIALIZED to CXA_GUARD_INITIALIZING.
+        int32_t expected = CXA_GUARD_UNINITIALIZED;
+        if (atomic_compare_exchange_weak_explicit(atomic_guard, &expected, CXA_GUARD_INITIALIZING,
+                                                  memory_order_release,
+                                                  memory_order_relaxed)) {
+            return 1; // Success! This core must execute the constructor
+        }
+    }
+}
+
+void __cxa_guard_release(int32_t *guard_object) {
+    _Atomic int32_t *atomic_guard = (_Atomic int32_t *)guard_object;
+
+    // set Bit 0 (done) and clear Bit 1 (unlocked)
+    atomic_store_explicit(atomic_guard, CXA_GUARD_INITIALIZED, memory_order_release);
+
+    // wake up any waiters
+    __sev();
+}
+
+void __cxa_guard_abort(int32_t *guard_object) {
+    _Atomic int32_t *atomic_guard = (_Atomic int32_t *)guard_object;
+
+    // reset back to uninitialized state
+    atomic_store_explicit(atomic_guard, CXA_GUARD_UNINITIALIZED, memory_order_release);
+
+    // wake up any waiters
+    __sev();
+}
+
+Clang_Pragma("clang diagnostic pop")
+#else
+
+int __cxa_guard_acquire(volatile int32_t *guard_object) {
+    int32_t guard_val = *guard_object;
+    if (guard_val == CXA_GUARD_INITIALIZED) {
+        return 0;
+    }
+    if (guard_val & CXA_GUARD_INITIALIZING) {
+        panic("recursive CXX initializer");
+    }
+    *guard_object = CXA_GUARD_INITIALIZING;
+    return 1;
+}
+
+void __cxa_guard_release(volatile int32_t *guard_object) {
+    *guard_object = CXA_GUARD_INITIALIZED;
+}
+
+void __cxa_guard_abort(volatile int32_t *guard_object) {
+    *guard_object = CXA_GUARD_UNINITIALIZED;
+}
+#endif

src/rp2_common/pico_clib_interface/llvm_libc_interface.c

@@ -9,7 +9,6 @@
 #include <stddef.h>
 #include <sys/time.h>
 #include <time.h>
-
 #include <llvm-libc-types/ssize_t.h>
 
 #include "pico/runtime_init.h"
@@ -79,7 +78,12 @@ bool __llvm_libc_timespec_get_utc(struct timespec *ts) {
     return true;
 }
 
-void __cxa_finalize(__unused void *dso) {}
+__weak void __cxa_finalize(__unused void *dso) {}
+
+__weak int atexit(void (*function)(void)) {
+    (void)function;
+    return 0;
+}
 
 void __attribute__((noreturn)) __llvm_libc_exit(__unused int status) {
 #if PICO_ENTER_USB_BOOT_ON_EXIT
@@ -120,5 +124,4 @@ void runtime_init(void) {
     for (void (**p)(void) = &__init_array_start; p < &__init_array_end; ++p) {
         (*p)();
     }
-}
-
+}

src/rp2_common/pico_clib_interface/llvm_libc_interface_cpp.cpp

@@ -0,0 +1,13 @@
+#include <version>
+#include <cstdarg>
+
+#include "pico.h"
+
+namespace std {
+    inline namespace __2 {
+        [[__noreturn__]] _LIBCPP_AVAILABILITY_VERBOSE_ABORT _LIBCPP_OVERRIDABLE_FUNC_VIS _LIBCPP_ATTRIBUTE_FORMAT(
+        __printf__, 1, 2) void __libcpp_verbose_abort(const char* __format, ...) _NOEXCEPT {
+            panic("c++ abort: %s", __format);
+        }
+    }
+}

src/rp2_common/pico_clib_interface/newlib_interface.c

@@ -47,6 +47,9 @@ void __attribute__((noreturn)) __weak _exit(__unused int status) {
 #endif
 }
 
+void __weak _fini(void) {
+}
+
 __weak void *_sbrk(int incr) {
     extern char end; /* Set by linker.  */
     static char *heap_end;

src/rp2_common/pico_clib_interface/picolibc_interface.c

@@ -85,6 +85,15 @@ void __attribute__((noreturn)) __weak _exit(__unused int status) {
 #endif
 }
 
+int __weak getpid(void) {
+    return 0;
+}
+
+int __weak kill(__unused int pid, __unused int sig) {
+    __breakpoint();
+    return -1;
+}
+
 static int64_t epoch_time_us_since_boot;
 
 __weak int gettimeofday (struct timeval *__restrict tv, __unused void *__restrict tz) {

src/rp2_common/pico_cxx_options/BUILD.bazel

@@ -14,9 +14,14 @@ pico_sdk_define(
 cc_library(
     name = "pico_cxx_options",
     srcs = ["new_delete.cpp"],
+    hdrs = [
+        "include/pico/cxx_options.h",
+    ],
+    includes = ["include"],
     target_compatible_with = compatible_with_rp2(),
     deps = [
         ":PICO_CXX_ENABLE_EXCEPTIONS",
-        "//src/rp2_common:pico_platform",
+        "//src:pico_platform_internal",
+        "//src/common/pico_base_headers",
     ],
 )

src/rp2_common/pico_cxx_options/CMakeLists.txt

@@ -4,6 +4,7 @@ if (NOT TARGET pico_cxx_options)
     target_sources(pico_cxx_options INTERFACE
         ${CMAKE_CURRENT_LIST_DIR}/new_delete.cpp
     )
+    target_include_directories(pico_cxx_options SYSTEM INTERFACE ${CMAKE_CURRENT_LIST_DIR}/include)
 
     # PICO_CMAKE_CONFIG: PICO_CXX_ENABLE_EXCEPTIONS, Enable CXX exception handling, type=bool, default=0, group=pico_cxx_options
     # PICO_BUILD_DEFINE: PICO_CXX_ENABLE_EXCEPTIONS, value of CMake var PICO_CXX_ENABLE_EXCEPTIONS, type=string, default=0, group=pico_cxx_options

src/rp2_common/pico_cxx_options/include/pico/cxx_options.h

@@ -0,0 +1,21 @@
+/*
+ * Copyright (c) 2026 Raspberry Pi (Trading) Ltd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#ifndef _PICO_CXX_OPTIONS_H
+#define _PICO_CXX_OPTIONS_H
+
+#include "pico.h"
+
+// PICO_CONFIG: PICO_CXX_DISABLE_ALLOCATION_OVERRIDES, Disable SDK overrides of C++ new/delete operators, type=bool, default=0, advanced=true, group=pico_cxx_options
+
+// PICO_CONFIG: PICO_CXX_THREAD_SAFE_STATIC_INIT, Enable thread/IRQ safe locks for C++ static initializers, type=bool, default=1 when using pico_multicore, advanced=true, group=pico_cxx_options
+#ifndef PICO_CXX_THREAD_SAFE_STATIC_INIT
+#define PICO_CXX_THREAD_SAFE_STATIC_INIT LIB_PICO_MULTICORE
+#endif
+
+#endif
+
+

src/rp2_common/pico_cxx_options/new_delete.cpp

@@ -3,12 +3,13 @@
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
+#include "pico/cxx_options.h"
 
 #if !PICO_CXX_ENABLE_EXCEPTIONS 
 // Override the standard allocators to use regular malloc/free
 
 #if !PICO_CXX_DISABLE_ALLOCATION_OVERRIDES // Let user override
-#include <stdlib.h> // weird looking but it is required if dropping picolibc on top of GCC+newlib (reent issue)
+#include <stdlib.h> // weird looking, but it is required if dropping picolibc on top of GCC+newlib (reent issue)
 #include <cstdlib>
 #include "pico.h"
 
@@ -20,7 +21,7 @@ void *operator new[](std::size_t n) {
     return std::malloc(n);
 }
 
-void operator delete(void *p) { std::free(p); }
+void operator delete(void *p) noexcept { std::free(p); }
 
 void operator delete[](void *p) noexcept { std::free(p); }
 

src/rp2_common/pico_standard_link/CMakeLists.txt

@@ -208,7 +208,7 @@ if (NOT TARGET pico_standard_link)
     # \brief\ Place time-critical code for the target into <MEMORY>
     #
     # Configures the target to run functions marked __time_critical_func() from <MEMORY> rather than
-    # normal SRAM, useful if <MEMORY> has dedicated AHB ports which are otherwise unused. For example, 
+    # normal SRAM, useful if <MEMORY> has dedicated AHB ports which are otherwise unused. For example,
     # xip_ram could be used in no_flash and copy_to_ram binaries, as the XIP AHB ports are unused.
     # This sets PICO_TIME_CRITICAL_PLACEMENT=__in_<MEMORY>, and any necessary defines required to use
     # <MEMORY> (e.g. PICO_USE_XIP_CACHE_AS_RAM=1 for xip_ram).
@@ -229,7 +229,7 @@ if (NOT TARGET pico_standard_link)
     # \brief\ Place time-critical code for the target into <MEMORY>
     #
     # Configures the target to place data (and code) marked __not_in_flash() in <MEMORY> rather than
-    # normal SRAM, useful if <MEMORY> has dedicated AHB ports which are otherwise unused. For example, 
+    # normal SRAM, useful if <MEMORY> has dedicated AHB ports which are otherwise unused. For example,
     # xip_ram could be used in no_flash and copy_to_ram binaries, as the XIP AHB ports are unused.
     # This sets PICO_NOT_IN_FLASH_PLACEMENT=__in_<MEMORY>, and any necessary defines required to use
     # <MEMORY> (e.g. PICO_USE_XIP_CACHE_AS_RAM=1 for xip_ram).
@@ -363,9 +363,10 @@ if (NOT TARGET pico_standard_link)
         target_compile_definitions(pico_standard_link INTERFACE PICO_DEOPTIMIZED_DEBUG=1)
     endif()
 
-    # this (arguably wrong) code is restored for 1.5.1 as setting -nostartfiles on many C++ binaries causes link errors. see issue #1368
-    # -nostartfiles will be added if PICO_NO_FLASH would be defined to 1
-    target_link_options(pico_standard_link INTERFACE $<$<IF:$<IN_LIST:$<TARGET_PROPERTY:PICO_TARGET_BINARY_TYPE>,${NO_FLASH_BINARY_TYPES}>,1,$<AND:$<IN_LIST:${PICO_DEFAULT_BINARY_TYPE},${NO_FLASH_BINARY_TYPES}>,$<STREQUAL:,$<TARGET_PROPERTY:PICO_TARGET_BINARY_TYPE>>>>:-nostartfiles>)
+    if (PICO_C_COMPILER_IS_GNU)
+        target_link_options(pico_standard_link INTERFACE -nostartfiles)
+    endif()
+
     # boot_stage2 will be linked if PICO_NO_FLASH would be defined to 0; note if boot_stage2 headers not present, then boot_stage2 is omitted from build anyway
     if (TARGET boot_stage2_headers)
         target_link_libraries(pico_standard_link INTERFACE $<$<NOT:$<IF:$<IN_LIST:$<TARGET_PROPERTY:PICO_TARGET_BINARY_TYPE>,${NO_FLASH_BINARY_TYPES}>,1,$<AND:$<IN_LIST:${PICO_DEFAULT_BINARY_TYPE},${NO_FLASH_BINARY_TYPES}>,$<STREQUAL:,$<TARGET_PROPERTY:PICO_TARGET_BINARY_TYPE>>>>>:$<IF:$<BOOL:$<TARGET_PROPERTY:PICO_TARGET_BOOT_STAGE2>>,$<TARGET_PROPERTY:PICO_TARGET_BOOT_STAGE2>,bs2_default>_library>)

src/rp2_common/pico_standard_link/script_include/section_copy_to_ram_data.incl

@@ -11,6 +11,7 @@
     __tls_base, __tls_end
     __tbss_end
     __global_pointer$
+    __dso_handle
 */
 
 SECTIONS
@@ -65,6 +66,7 @@ SECTIONS
         *(SORT(.fini_array.*))
         *(.fini_array)
         PROVIDE_HIDDEN (__fini_array_end = .);
+        PROVIDE(__dso_handle = 0);
 
         *(.jcr)
         . = ALIGN(4);