Copyright © 2018 Keith Packard 🄯

This is a fork of newlib which integrates the stdio code from gcc-avr to make it much smaller for tiny embedded systems. There's debian packaging which builds for arm-none-eabi targets.

I've tried to expose all of the same code selection options that are provided in the autotools. Use -D={true,false} to change from the default value.

Unlike autotools, which has you specify all of the cross-compilation bits on the command line, meson sticks them in a separate configuration file. There are a bunch of things you need to set, which the build system really shouldn't care about. In any case, you can find the cross-compilation details for the arm-none-eabi toolchain in the cross-arm-none-eabi.txt file:

[binaries]
c = 'arm-none-eabi-gcc'
ar = 'arm-none-eabi-ar'
as = 'arm-none-eabi-as'

[host_machine]
system = ''
cpu_family = ''
cpu = ''
endian = ''

If those programs aren't in your path, you can edit the file to point wherever they may be.

The key trick here is that the meson configuration, just like the autotools configuration it replaces, figures out all of the target CPU architectures supported by the compiler by doing:

$ arm-none-eabi-gcc --print-multi-lib
.;
thumb;@mthumb
hard;@mfloat-abi=hard
thumb/v6-m;@mthumb@march=armv6s-m
thumb/v7-m;@mthumb@march=armv7-m
thumb/v7e-m;@mthumb@march=armv7e-m
thumb/v7-ar;@mthumb@march=armv7
thumb/v8-m.base;@mthumb@march=armv8-m.base
thumb/v8-m.main;@mthumb@march=armv8-m.main
thumb/v7e-m/fpv4-sp/softfp;@mthumb@march=armv7e-m@mfpu=fpv4-sp-d16@mfloat-abi=softfp
thumb/v7e-m/fpv4-sp/hard;@mthumb@march=armv7e-m@mfpu=fpv4-sp-d16@mfloat-abi=hard
thumb/v7e-m/fpv5/softfp;@mthumb@march=armv7e-m@mfpu=fpv5-d16@mfloat-abi=softfp
thumb/v7e-m/fpv5/hard;@mthumb@march=armv7e-m@mfpu=fpv5-d16@mfloat-abi=hard
thumb/v7-ar/fpv3/softfp;@mthumb@march=armv7@mfpu=vfpv3-d16@mfloat-abi=softfp
thumb/v7-ar/fpv3/hard;@mthumb@march=armv7@mfpu=vfpv3-d16@mfloat-abi=hard
thumb/v7-ar/fpv3/hard/be;@mthumb@march=armv7@mfpu=vfpv3-d16@mfloat-abi=hard@mbig-endian
thumb/v8-m.main/fpv5-sp/softfp;@mthumb@march=armv8-m.main@mfpu=fpv5-sp-d16@mfloat-abi=softfp
thumb/v8-m.main/fpv5-sp/hard;@mthumb@march=armv8-m.main@mfpu=fpv5-sp-d16@mfloat-abi=hard
thumb/v8-m.main/fpv5/softfp;@mthumb@march=armv8-m.main@mfpu=fpv5-d16@mfloat-abi=softfp
thumb/v8-m.main/fpv5/hard;@mthumb@march=armv8-m.main@mfpu=fpv5-d16@mfloat-abi=hard

Yes, we're going to compile all of the code 20 times with the specified compiler options (replace the '@'s with '-' to see what they will be).

Because I'm targeting smaller systems like the STM32F042 Cortex-M0 parts with 4kB of RAM and 32kB of flash, I enable all of the 'make it smaller' options. This example is in the do-arm-configure file:

#!/bin/sh
ARCH=arm-none-eabi
DIR=`dirname $0`
meson $DIR \
    -Dtarget-optspace=true \
    -Dnewlib-tinystdio=true \
    -Dnewlib-supplied-syscalls=false \
    -Dnewlib-reentrant-small=true\
    -Dnewlib-wide-orient=false\
    -Dnewlib-nano-malloc=true\
    -Dlite-exit=true\
    -Dnewlib-global-atexit=true\
    -Dincludedir=lib/newlib-nano/$ARCH/include \
    -Dlibdir=lib/newlib-nano/$ARCH/lib \
    --cross-file $DIR/cross-$ARCH.txt \
    --buildtype plain

Note the use of '--buildtype plain'. This stops meson from adding compilation options so that the '-Dtarget-optspace=true' option can select '-Os'.

This script is designed to be run from a build directory, so you'd do:

$ mkdir build-arm-none-eabi
$ cd build-arm-none-eabi
$ ../do-arm-configure

Once configured, you can compile the libraries with

$ ninja
...
$ ninja install
...
$

Eventually, we could go configure the compiler so that selecting a suitable target architecture combination would set up the library paths to match, but for now you'll have to figure out the right -L line by yourself by matching the path name on the left side of the --print-multi-lib output with the compiler options on the right side. For instance, my STM32F042 cortex-M0 parts use

$ arm-none-eabi-gcc -mlittle-endian -mcpu=cortex-m0 -mthumb

To gcc, '-mcpu=cortex=m0' is the same as '-march=armv6s-m', so looking at the output above, the libraries we want are in

/usr/local/lib/newlib-nano/arm-none-eabi/lib/thumb/v6-m

so, to link, we need to use:

$ arm-none-eabi-gcc ... -L/usr/local/lib/newlib-nano/arm-none-eabi/lib/thumb/v6-m -lm -lc -lgcc

If you want to compile the library for your local processor to test changes in the library, the meson configuration is happy to do that for you. You won't need a meson cross compilation configuration file, so all you need is the right compile options. They're mostly the same as the embedded version, but you don't want the multi-architecture stuff and I prefer plain debug to an -Os, as that makes debugging the library easier.

The do-native-configure script has an example:

#!/bin/sh
DIR=`dirname $0`
meson $DIR \
    -Dmultilib=false \
    -Dnewlib-tinystdio=true \
    -Dnewlib-supplied-syscalls=false \
    -Dnewlib-wide-orient=false\
    -Dnewlib-nano-malloc=true\
    -Dlite-exit=true\
    -Dnewlib-global-atexit=true\
    -Dincludedir=lib/newlib-nano/include \
    -Dlibdir=lib/newlib-nano/lib \
    -Dtests=true \
    --buildtype debug

Again, create a directory and build there:

$ mkdir build-native
$ cd build-native
$ ../do-native-configure
$ ninja

This will also build a test case for printf and scanf in the 'test' directory, which I used to fix up the floating point input and output code.