Use picolibc on arm devices

lib/python/qmk/cli/doctor/check.py

@@ -88,16 +88,21 @@ def _check_arm_gcc_installation():
         temp_in = Path(temp_dir) / 'test.c'
         temp_out = Path(temp_dir) / 'test.elf'
 
-        temp_in.write_text('#include <newlib.h>\nint main() { return __NEWLIB__ * __NEWLIB_MINOR__ * __NEWLIB_PATCHLEVEL__; }', encoding='utf-8')
+        temp_in.write_text('#include <stdlib.h>\nint main(void) { return EXIT_SUCCESS; }', encoding='utf-8')
 
         args = ['arm-none-eabi-gcc', '-mcpu=cortex-m0', '-mthumb', '-mno-thumb-interwork', '--specs=nosys.specs', '--specs=nano.specs', '-x', 'c', '-o', str(temp_out), str(temp_in)]
         result = cli.run(args, stdout=None, stderr=None)
         if result.returncode == 0:
-            cli.log.info('Successfully compiled using arm-none-eabi-gcc')
+            cli.log.info('Successfully compiled using arm-none-eabi-gcc with newlib')
         else:
-            cli.log.error(f'Failed to compile a simple program with arm-none-eabi-gcc, return code {result.returncode}')
-            cli.log.error(f'Command: {" ".join(args)}')
-            return CheckStatus.ERROR
+            args = ['arm-none-eabi-gcc', '-x', 'c', '-o', str(temp_out), str(temp_in)]
+            result = cli.run(args, stdout=None, stderr=None)
+            if result.returncode == 0:
+                cli.log.info('Successfully compiled using arm-none-eabi-gcc with picolibc')
+            else:
+                cli.log.error(f'Failed to compile a simple program with arm-none-eabi-gcc, return code {result.returncode}')
+                cli.log.error(f'Command: {" ".join(args)}')
+                return CheckStatus.ERROR
 
         args = ['arm-none-eabi-size', str(temp_out)]
         result = cli.run(args, stdout=None, stderr=None)

platforms/chibios/platform.mk

@@ -423,8 +423,23 @@ else
     TOOLCHAIN ?= arm-none-eabi-
 
     # Toolchain specific Linker flags
-    TOOLCHAIN_LDFLAGS = -Wl,--no-wchar-size-warning \
-                        --specs=nano.specs
+    TOOLCHAIN_LDFLAGS = -Wl,--no-wchar-size-warning
+
+    # Default to compiling with picolibc for ARM targets if available, which
+    # is available by default on distributions based on Debian 11+.
+    ifeq ($(shell $(TOOLCHAIN)gcc --specs=picolibc.specs -E - 2>/dev/null >/dev/null </dev/null ; echo $$?),0)
+        # Toolchain specific Compiler flags Note that we still link with our own
+        # linker script by providing it via the -T flag in SHARED_LDFLAGS.
+        TOOLCHAIN_CFLAGS = --specs=picolibc.specs
+
+        # picolibc internally uses __heap_start and __heap_end instead of the
+        # defacto chibios linker script standard __heap_base__ and __heap_end__
+        # therefore we introduce these symbols as an alias.
+        TOOLCHAIN_LDSYMBOLS = -Wl,--defsym=__heap_start=__heap_base__,--defsym=__heap_end=__heap_end__
+
+        # Tell QMK that we are compiling with picolibc.
+        OPT_DEFS += -DUSE_PICOLIBC
+    endif
 
     # MCU architecture flags
     MCUFLAGS = -mcpu=$(MCU) \

platforms/chibios/syscall-fallbacks.c

@@ -18,6 +18,7 @@
 #include <sys/stat.h>
 #include <sys/types.h>
 
+#ifndef __PICOLIBC__
 /* To compile the ChibiOS syscall stubs with picolibc
  * the _reent struct has to be defined. */
 #if defined(USE_PICOLIBC)
@@ -113,3 +114,4 @@ __attribute__((weak, used)) void __cxa_pure_virtual(void) {
 }
 
 #pragma GCC diagnostic pop
+#endif