Copyright ยฉ 2018 Keith Packard ๐ฏ
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.
This fork github.com/lupyuen/newlib
was created to allow building under PlatformIO and with CODAL to support MakeCode for STM32 Blue Pill. See https://github.com/lupyuen/codal-libopencm3
The files and folders added in this fork:
-
library.json
for PlatformIO support -
scripts
folder for CODAL build -
build-arm-none-eabi
folder for CODAL build -
include/newlib-force.h
to force newlib to be linked
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.
Option | Default | Description |
---|---|---|
target-optspace | false | Compile with -Os |
hw-fp | false | Turn on hardware floating point math |
tests | false | Enable tests |
newlib-tinystdio | false | Use tiny stdio from avr libc |
newlib-io-pos-args | false | Enable printf-family positional arg support |
newlib-io-c99-formats | false | Enable C99 support in IO functions like printf/scanf |
newlib-register-fini | false | Enable finalization function registration using atexit |
newlib-io-long-long | false | Enable long long type support in IO functions like printf/scanf |
newlib-io-long-double | false | Enable long double type support in IO functions printf/scanf |
newlib-mb | false | Enable multibyte support |
newlib-iconv-encodings | false | Enable specific comma-separated list of bidirectional iconv encodings to be built-in |
newlib-iconv-from-encodings | false | Enable specific comma-separated list of "from" iconv encodings to be built-in |
newlib-iconv-to-encodings | false | Enable specific comma-separated list of "to" iconv encodings to be built-in |
newlib-iconv-external-ccs | false | Enable capabilities to load external CCS files for iconv |
newlib-atexit-dynamic-alloc | false | Enable dynamic allocation of atexit entries |
newlib-global-atexit | false | Enable atexit data structure as global |
newlib-reent-small | false | Enable small reentrant struct support |
newlib-global-stdio-streams | false | Enable global stdio streams |
newlib-fvwrite-in-streamio | false | Disable iov in streamio |
newlib-fseek-optimization | false | Disable fseek optimization |
newlib_wide_orient | false | Turn off wide orientation in streamio |
newlib-nano-malloc | false | Use small-footprint nano-malloc implementation |
newlib-unbuf-stream-opt | false | Enable unbuffered stream optimization in streamio |
lite-exit | false | Enable light weight exit |
newlib_nano_formatted_io | false | Use nano version formatted IO |
newlib-retargetable-locking | false | Allow locking routines to be retargeted at link time |
newlib-long-time_t | false | Define time_t to long |
newlib-multithread | false | Enable support for multiple threads |
newlib-iconv | false | Enable iconv library support |
newlib-io-float | false | Enable printf/scanf family float support |
newlib-supplied-syscalls | false | Enable newlib supplied syscalls |
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.