Add picolibc support [v2]

This adds support for using picolibc instead of newlib on embedded
systems.

Signed-off-by: Keith Packard <keithp@keithp.com>

v2:
	Add check for meson and ninja
	Sync option default values with current picolibc defaults
	Remove xtensa sys header file install as those aren't in picolibc

1 files changed, 111 insertions, 0 deletions

diff --git a/scripts/build/libc/picolibc.sh b/scripts/build/libc/picolibc.sh
new file mode 100644
index 00000000..3c22def3
--- /dev/null
+++ b/scripts/build/libc/picolibc.sh
@@ -0,0 +1,111 @@
+# This file adds functions to build the Picolibc library
+# Copyright © 2020 Keith Packard
+# Licensed under the GPL v2 or later. See COPYING in the root of this package
+#
+# Edited by Keith Packard <keithp@keithp.com>
+#
+
+picolibc_start_files()
+{
+    CT_DoStep INFO "Installing C library headers & start files"
+    CT_DoExecLog ALL cp -a "${CT_SRC_DIR}/picolibc/newlib/libc/include/." \
+    "${CT_HEADERS_DIR}"
+    CT_EndStep
+}
+
+picolibc_main()
+{
+    local -a picolibc_opts
+    local cflags_for_target
+
+    CT_DoStep INFO "Installing C library"
+
+    CT_mkdir_pushd "${CT_BUILD_DIR}/build-libc"
+
+    CT_DoLog EXTRA "Configuring C library"
+
+    # Multilib is the default, so if it is not enabled, disable it.
+    if [ "${CT_MULTILIB}" != "y" ]; then
+        picolibc_opts+=("-Dmultilib=false")
+    fi
+
+    yn_args="IO_C99FMT:io-c99-formats
+IO_LL:io-long-long
+REGISTER_FINI:newlib-register-fini
+NANO_MALLOC:newlib-nano-malloc
+ATEXIT_DYNAMIC_ALLOC:newlib-atexit-dynamic-alloc
+GLOBAL_ATEXIT:newlib-global-atexit
+LITE_EXIT:lite-exit
+MULTITHREAD:newlib-multithread
+RETARGETABLE_LOCKING:newlib-retargetable-locking
+    "
+
+    for ynarg in $yn_args; do
+        var="CT_LIBC_PICOLIBC_${ynarg%:*}"
+        eval var=\$${var}
+        argument=${ynarg#*:}
+
+
+        if [ "${var}" = "y" ]; then
+            picolibc_opts+=( "-D$argument=true" )
+        else
+            picolibc_opts+=( "-D$argument=false" )
+        fi
+    done
+
+    [ "${CT_USE_SYSROOT}" = "y" ] && \
+	picolibc_opts+=( "-Dsysroot-install=true" )
+
+    [ "${CT_LIBC_PICOLIBC_EXTRA_SECTIONS}" = "y" ] && \
+        CT_LIBC_PICOLIBC_TARGET_CFLAGS="${CT_LIBC_PICOLIBC_TARGET_CFLAGS} -ffunction-sections -fdata-sections"
+
+    [ "${CT_LIBC_PICOLIBC_LTO}" = "y" ] && \
+        CT_LIBC_PICOLIBC_TARGET_CFLAGS="${CT_LIBC_PICOLIBC_TARGET_CFLAGS} -flto"
+
+    cflags_for_target="${CT_ALL_TARGET_CFLAGS} ${CT_LIBC_PICOLIBC_TARGET_CFLAGS}"
+
+    # Note: picolibc handles the build/host/target a little bit differently
+    # than one would expect:
+    #   build  : not used
+    #   host   : the machine building picolibc
+    #   target : the machine picolibc runs on
+	meson_cflags=""
+	for cflag in ${cflags_for_target}; do
+		meson_cflags="${meson_cflags} '${cflag}',"
+	done
+	cat << EOF > picolibc-cross.txt
+[binaries]
+c = '${CT_TARGET}-gcc'
+ar = '${CT_TARGET}-ar'
+as = '${CT_TARGET}-as'
+strip = '${CT_TARGET}-strip'
+
+[host_machine]
+system = 'none'
+cpu_family = 'arm'
+cpu = 'arm'
+endian = 'little'
+
+[properties]
+c_args = [ ${meson_cflags} '-nostdlib', '-fno-common', '-ftls-model=local-exec' ]
+needs_exe_wrapper = true
+skip_sanity_check = true
+EOF
+    CT_DoExecLog CFG                                               \
+    meson                                                          \
+        --cross-file picolibc-cross.txt                            \
+        --prefix=${CT_SYSROOT_DIR}                                 \
+	-Dspecsdir=${CT_SYSROOT_DIR}/lib                           \
+        "${CT_SRC_DIR}/picolibc"                                   \
+        "${picolibc_opts[@]}"                                      \
+        "${CT_LIBC_PICOLIBC_EXTRA_CONFIG_ARRAY[@]}"
+
+    CT_DoLog EXTRA "Building C library"
+    CT_DoExecLog ALL ninja
+
+    CT_DoLog EXTRA "Installing C library"
+    CT_DoExecLog ALL ninja install
+
+    CT_Popd
+    CT_EndStep
+}