Incorporate picolibc into the build process

Right now it is still limited as it compiles only for one target,
but it should be possible to build BIOS with one command

Tested with digilent_arty.py

litex/soc/integration/builder.py

@@ -41,6 +41,7 @@ soc_software_packages = [
 
     # LiteX cores.
     "libbase",
+    "libc",
 
     # LiteX Ecosystem cores.
     "libfatfs",
@@ -138,8 +139,10 @@ class Builder:
         for k, v in export.get_cpu_mak(self.soc.cpu, self.compile_software):
             define(k, v)
 
-        # Define the SoC/Compiler-RT/Software/Include directories.
+        # Define the SoC/Picolibc/Compiler-RT/Software/Include directories.
         define("SOC_DIRECTORY", soc_directory)
+        picolibc_directory = get_data_mod("software", "picolibc").data_location
+        define("PICOLIBC_DIRECTORY", picolibc_directory)
         compiler_rt_directory = get_data_mod("software", "compiler_rt").data_location
         define("COMPILER_RT_DIRECTORY", compiler_rt_directory)
         variables_contents.append("export BUILDINC_DIRECTORY")

litex/soc/software/libc/Makefile

@@ -0,0 +1,7 @@
+include ../include/generated/variables.mak
+include $(SOC_DIRECTORY)/software/common.mak
+
+newlib/libc.a:
+	$(LIBC_DIRECTORY)/do-rv32im-configure $(PICOLIBC_DIRECTORY)
+	meson compile
+	sh $(LIBC_DIRECTORY)/swap_libc.sh

litex/soc/software/libc/cross-rv32im.txt

@@ -0,0 +1,18 @@
+[binaries]
+c = 'riscv64-unknown-elf-gcc'
+ar = 'riscv64-unknown-elf-ar'
+as = 'riscv64-unknown-elf-as'
+nm = 'riscv64-unknown-elf-nm'
+strip = 'riscv64-unknown-elf-strip'
+
+[host_machine]
+system = 'unknown'
+cpu_family = 'riscv'
+cpu = 'riscv32'
+endian = 'little'
+
+[properties]
+c_args = [ '-nostdlib', '-mno-save-restore', '-march=rv32im', '-mabi=ilp32']
+c_link_args = [ '-nostdlib', '-mno-save-restore', '-march=rv32im', '-mabi=ilp32']
+skip_sanity_check = true
+

litex/soc/software/libc/do-rv32im-configure

@@ -0,0 +1,11 @@
+#!/bin/sh
+
+ARCH=riscv64-unknown-elf
+DIR=`dirname $0`
+meson "$1" \
+        -Dtests=true \
+        -Dmultilib=false \
+        -Dincludedir="picolibc/$ARCH/include" \
+        -Dlibdir="picolibc/$ARCH/lib" \
+        --cross-file "$DIR/cross-rv32im.txt" \
+

litex/soc/software/libc/swap_libc.sh

@@ -0,0 +1,58 @@
+#!/bin/sh
+
+AR=riscv64-unknown-elf-ar
+
+for obj in \
+    vsnprintf.c.o \
+    vfprintf.c.o \
+    fputc.c.o \
+    filestrput.c.o \
+    dtoa_ryu.c.o \
+    ryu_table.c.o \
+    ryu_umul128.c.o \
+    ryu_log10.c.o \
+    ryu_log2pow5.c.o \
+    ryu_pow5bits.c.o \
+    ryu_divpow2.c.o \
+    qsort.c.o \
+    strchr.c.o \
+    strpbrk.c.o \
+    strrchr.c.o \
+    strcpy.c.o \
+    strncpy.c.o \
+    strcmp.S.o \
+    strncmp.c.o \
+    strcat.c.o \
+    strncat.c.o \
+    strlen.c.o \
+    strnlen.c.o \
+    strspn.c.o \
+    memcmp.c.o \
+    memset.S.o \
+    memcpy.c.o \
+    memmove.S.o \
+    strstr.c.o \
+    memchr.c.o \
+    strtoul.c.o \
+    strtol.c.o \
+    snprintf.c.o \
+    sprintf.c.o \
+    rand.c.o \
+    srand.c.o \
+    abort.c.o \
+    errno.c.o \
+    strerror.c.o \
+    strtod.c.o \
+    ctype_.c.o \
+    locale.c.o \
+    mbtowc_r.c.o \
+    wctomb_r.c.o \
+    strcasecmp.c.o \
+    isdigit.c.o \
+; do
+    $AR x "newlib/libc.a" $obj
+    $AR csr "../libbase/libbase.a" $obj
+    $AR csr "../libbase/libbase-nofloat.a" $obj
+    rm $obj
+done
+