Picolibc optimizations

CMakeLists.txt

@@ -917,6 +917,9 @@ if(CONFIG_USERSPACE)
   if(CONFIG_NEWLIB_LIBC_NANO)
     set(NEWLIB_PART -l libc_nano.a z_libc_partition -l libm_nano.a z_libc_partition)
   endif()
+  if(CONFIG_PICOLIBC)
+    set(NEWLIB_PART -l libc.a z_libc_partition)
+  endif()
 
   add_custom_command(
     OUTPUT ${APP_SMEM_UNALIGNED_LD} ${APP_SMEM_PINNED_UNALIGNED_LD}

arch/Kconfig

@@ -33,7 +33,7 @@ config ARM
 	# FIXME: current state of the code for all ARM requires this, but
 	# is really only necessary for Cortex-M with ARM MPU!
 	select GEN_PRIV_STACKS
-	select ARCH_HAS_THREAD_LOCAL_STORAGE if CPU_AARCH32_CORTEX_R || CPU_CORTEX_M
+	select ARCH_HAS_THREAD_LOCAL_STORAGE if CPU_AARCH32_CORTEX_R || CPU_CORTEX_M || CPU_AARCH32_CORTEX_A
 	help
 	  ARM architecture
 

arch/arm/core/aarch32/cortex_a_r/CMakeLists.txt

@@ -15,3 +15,4 @@ zephyr_library_sources(
   )
 
 zephyr_library_sources_ifdef(CONFIG_USERSPACE thread.c)
+zephyr_library_sources_ifdef(CONFIG_THREAD_LOCAL_STORAGE __aeabi_read_tp.S)

arch/arm/core/aarch32/cortex_a_r/__aeabi_read_tp.S

@@ -0,0 +1,20 @@
+/*
+ * Copyright (c) 2020 Intel Corporation
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <toolchain.h>
+
+_ASM_FILE_PROLOGUE
+
+GTEXT(__aeabi_read_tp)
+
+SECTION_FUNC(text, __aeabi_read_tp)
+	/*
+	 * Load TLS base address, which is stored in the TPIDRURO register, also
+	 * known as the "Process ID" register. Refer to the code in z_arm_pendsv
+	 * to see where this register is set.
+	 */
+	mrc 15, 0, r0, c13, c0, 3
+	bx lr

arch/arm/core/aarch32/swap_helper.S

@@ -186,7 +186,7 @@ out_fp_endif:
     adds r4, r2, r4
     ldr r0, [r4]
 
-#if defined(CONFIG_CPU_AARCH32_CORTEX_R)
+#if defined(CONFIG_CPU_AARCH32_CORTEX_R) || defined(CONFIG_CPU_AARCH32_CORTEX_A)
     /* Store TLS pointer in the "Process ID" register.
      * This register is used as a base pointer to all
      * thread variables with offsets added by toolchain.

cmake/toolchain/gnuarmemb/generic.cmake

@@ -28,5 +28,6 @@ set(SYSROOT_TARGET       arm-none-eabi)
 set(CROSS_COMPILE ${TOOLCHAIN_HOME}/bin/${CROSS_COMPILE_TARGET}-)
 set(SYSROOT_DIR   ${TOOLCHAIN_HOME}/${SYSROOT_TARGET})
 set(TOOLCHAIN_HAS_NEWLIB ON CACHE BOOL "True if toolchain supports newlib")
+set(TOOLCHAIN_HAS_PICOLIBC ON CACHE BOOL "True if toolchain supports picolibc")
 
 message(STATUS "Found toolchain: gnuarmemb (${GNUARMEMB_TOOLCHAIN_PATH})")

cmake/toolchain/xtools/generic.cmake

@@ -33,6 +33,7 @@ set(SYSROOT_TARGET ${CROSS_COMPILE_TARGET})
 set(CROSS_COMPILE ${some_toolchain_root}/${CROSS_COMPILE_TARGET}/bin/${CROSS_COMPILE_TARGET}-)
 set(SYSROOT_DIR   ${some_toolchain_root}/${SYSROOT_TARGET}/${SYSROOT_TARGET})
 set(TOOLCHAIN_HAS_NEWLIB ON CACHE BOOL "True if toolchain supports newlib")
+set(TOOLCHAIN_HAS_PICOLIBC ON CACHE BOOL "True if toolchain supports picolibc")
 
 unset(some_toolchain_root)
 unset(some_toolchain)

include/sys/libc-hooks.h

@@ -16,7 +16,7 @@
  * that need to call into the kernel as system calls
  */
 
-#if defined(CONFIG_NEWLIB_LIBC) || defined(CONFIG_ARCMWDT_LIBC)
+#if defined(CONFIG_NEWLIB_LIBC) || defined(CONFIG_ARCMWDT_LIBC) || defined(CONFIG_PICOLIBC)
 
 /* syscall generation ignores preprocessor, ensure this is defined to ensure
  * we don't have compile errors
@@ -56,7 +56,21 @@ extern struct k_mem_partition z_malloc_partition;
  */
 #define Z_MALLOC_PARTITION_EXISTS 1
 #endif /* CONFIG_MINIMAL_LIBC_MALLOC_ARENA_SIZE > 0 */
-#endif /* CONFIG_MINIMAL_LIBC */
+#elif defined(CONFIG_PICOLIBC)
+/* If we are using picolibc, the heap arena is in one of two areas:
+ *  - If we have an MPU that requires power of two alignment, the heap bounds
+ *    must be specified in Kconfig via CONFIG_PICOLIBC_ALIGNED_HEAP_SIZE.
+ *  - Otherwise, the heap arena on most arches starts at a suitably
+ *    aligned base addreess after the `_end` linker symbol, through to the end
+ *    of system RAM.
+ */
+#if (!defined(CONFIG_MPU_REQUIRES_POWER_OF_TWO_ALIGNMENT) || \
+(defined(CONFIG_MPU_REQUIRES_POWER_OF_TWO_ALIGNMENT) && \
+CONFIG_PICOLIBC_ALIGNED_HEAP_SIZE))
+#define Z_MALLOC_PARTITION_EXISTS 1
+extern struct k_mem_partition z_malloc_partition;
+#endif
+#endif /* CONFIG_PICOLIBC */
 
 #ifdef Z_MALLOC_PARTITION_EXISTS
 /* Memory partition containing the libc malloc arena. Configuration controls
@@ -66,7 +80,7 @@ extern struct k_mem_partition z_malloc_partition;
 #endif
 
 #if defined(CONFIG_NEWLIB_LIBC) || defined(CONFIG_STACK_CANARIES) || \
-    defined(CONFIG_NEED_LIBC_MEM_PARTITION)
+defined(CONFIG_PICOLIBC) || defined(CONFIG_NEED_LIBC_MEM_PARTITION)
 /* - All newlib globals will be placed into z_libc_partition.
  * - Minimal C library globals, if any, will be placed into
  *   z_libc_partition.

include/sys/printk.h

@@ -60,11 +60,22 @@ static inline __printf_like(1, 0) void vprintk(const char *fmt, va_list ap)
 }
 #endif
 
+#ifdef _PICOLIBC__
+
+#include <stdio.h>
+
+#define snprintk(...) snprintf(__VA_ARGS__)
+#define vsnprintk(str, size, fmt, ap) vsnprintf(str, size, fmt, ap)
+
+#else
+
 extern __printf_like(3, 4) int snprintk(char *str, size_t size,
 					const char *fmt, ...);
 extern __printf_like(3, 0) int vsnprintk(char *str, size_t size,
 					  const char *fmt, va_list ap);
 
+#endif
+
 #ifdef __cplusplus
 }
 #endif

kernel/Kconfig

@@ -202,9 +202,17 @@ config THREAD_USERSPACE_LOCAL_DATA
 	depends on USERSPACE
 	default y if ERRNO && !ERRNO_IN_TLS
 
+config LIBC_ERRNO
+	bool
+	help
+	  Use external libc errno, not the internal one. This makes sure that
+	  ERRNO is not set for libc configurations that provide their own
+	  implementation.
+
 config ERRNO
 	bool "Errno support"
 	default y
+	depends on !LIBC_ERRNO
 	help
 	  Enable per-thread errno in the kernel. Application and library code must
 	  include errno.h provided by the C library (libc) to use the errno

kernel/errno.c

@@ -44,10 +44,13 @@ static inline int *z_vrfy_z_errno(void)
 #include <syscalls/z_errno_mrsh.c>
 
 #else
+#ifndef CONFIG_LIBC_ERRNO
 int *z_impl_z_errno(void)
 {
 	return &_current->errno_var;
 }
+#endif /* CONFIG_PICOLIBC */
+
 #endif /* CONFIG_USERSPACE */
 
 #endif /* CONFIG_ERRNO_IN_TLS */

lib/libc/CMakeLists.txt

@@ -8,4 +8,6 @@ elseif(CONFIG_MINIMAL_LIBC)
   add_subdirectory(minimal)
 elseif(CONFIG_ARMCLANG_STD_LIBC)
   add_subdirectory(armstdc)
+elseif(CONFIG_PICOLIBC)
+  add_subdirectory(picolibc)
 endif()

lib/libc/Kconfig

@@ -29,6 +29,15 @@ config MINIMAL_LIBC
 	help
 	  Build with minimal C library.
 
+config PICOLIBC
+	bool "Picolibc library"
+	depends on !NATIVE_APPLICATION
+	select THREAD_LOCAL_STORAGE if ARCH_HAS_THREAD_LOCAL_STORAGE
+	select LIBC_ERRNO
+	help
+	  Build with picolibc library. The picolibc library is expected to be
+	  part of the SDK in this case.
+
 config NEWLIB_LIBC
 	bool "Newlib C library"
 	depends on !NATIVE_APPLICATION
@@ -53,6 +62,30 @@ endchoice # LIBC_IMPLEMENTATION
 config HAS_NEWLIB_LIBC_NANO
 	bool
 
+if PICOLIBC
+
+config PICOLIBC_INTEGER_PRINTF
+	bool "Build with picolibc integer-only printf"
+	help
+	  Build with floating point printf disabled. This will reduce the size
+	  of the image.
+
+config PICOLIBC_ALIGNED_HEAP_SIZE
+	int "Picolibc aligned heap size (bytes)"
+	depends on MPU_REQUIRES_POWER_OF_TWO_ALIGNMENT
+	depends on USERSPACE
+	default 0
+	help
+	  If user mode is enabled, and MPU hardware has requirements that
+	  regions be sized to a power of two and aligned to their size,
+	  and user mode threads need to access this heap, then this is necessary
+	  to properly define an MPU region for the heap.
+
+	  If this is left at 0, then remaining system RAM will be used for this
+	  area and it may not be possible to program it as an MPU region.
+
+endif # PICOLIBC
+
 if NEWLIB_LIBC
 
 config NEWLIB_LIBC_NANO

lib/libc/picolibc/CMakeLists.txt

@@ -0,0 +1,41 @@
+# SPDX-License-Identifier: Apache-2.0
+
+zephyr_library()
+zephyr_library_sources(libc-hooks.c)
+
+# Zephyr normally uses -ffreestanding, which with current GNU toolchains
+# means that the flag macros used by picolibc <inttypes.h> to signal
+# support for PRI.64 macros are not present.  To make them available we
+# need to hook into the include path before the system files and
+# explicitly include the picolibc header that provides those macros.
+zephyr_include_directories(include)
+
+# define __LINUX_ERRNO_EXTENSIONS__ so we get errno defines like -ESHUTDOWN
+# used by the network stack
+zephyr_compile_definitions(__LINUX_ERRNO_EXTENSIONS__)
+
+zephyr_link_libraries(
+  m
+  c
+  gcc # Lib C depends on libgcc.
+  )
+
+# The -T/dev/null avoids pulling in picolibc.ld
+zephyr_link_libraries(
+  --specs=picolibc.specs
+  -T/dev/null
+  )
+
+zephyr_compile_options(
+  --specs=picolibc.specs
+  -D_GNU_SOURCE
+  )
+
+if(CONFIG_PICOLIBC_INTEGER_PRINTF)
+  zephyr_compile_options(
+    -DPICOLIBC_INTEGER_PRINTF_SCANF
+    )
+  zephyr_link_libraries(
+    -DPICOLIBC_INTEGER_PRINTF_SCANF
+    )
+endif()