This commit adds some documentation on what are the limitations of using
Picolibc as a standard C library for native modules.
This also contains a reference to the "errno" issue when building
natmods on RV32 that the PR this commit is part of, as it is not obvious
how to approach this issue when encountered for the first time.
Signed-off-by: Alessandro Gatti <a.gatti@frob.it>
This commit lets mpy_ld.py resolve symbols not only from the object
files involved in the linking process, or from compiler-supplied static
libraries, but also from a list of symbols referenced by an absolute
address (usually provided by the system's ROM).
This is needed for ESP8266 targets as some C stdlib functions are
provided by the MCU's own ROM code to reduce the final code footprint,
and therefore those functions' implementation was removed from the
compiler's support libraries. This means that unless `LINK_RUNTIME` is
set (which lets tooling look at more libraries to resolve symbols) the
build process will fail as tooling is unaware of the ROM symbols'
existence. With this change, fixed-address symbols can be exposed to
the symbol resolution step when performing natmod linking.
If there are symbols coming in from a fixed-address symbols list and
internal code or external libraries, the fixed-address symbol address
will take precedence in all cases.
Although this is - in theory - also working for the whole range of ESP32
MCUs, testing is currently limited to Xtensa processors and the example
natmods' makefiles only make use of this commit's changes for the
ESP8266 target.
Natmod builds can set the MPY_EXTERN_SYM_FILE variable pointing to a
linkerscript file containing a series of symbols (weak or strong) at a
fixed address; these symbols will then be used by the MicroPython
linker when packaging the natmod. If a different natmod build method is
used (eg. custom CMake scripts), `tools/mpy_ld.py` can now accept a
command line parameter called `--externs` (or its short variant `-e`)
that contains the path of a linkerscript file with the fixed-address
symbols to use when performing the linking process.
The linkerscript file parser can handle a very limited subset of
binutils's linkerscript syntax, namely just block comments, strong
symbols, and weak symbols. Each symbol must be in its own line for the
parser to succeed, empty lines or comment blocks are skipped. For an
example of what this parser was meant to handle, you can look at
`ports/esp8266/boards/eagle.rom.addr.v6.ld` and follow its format.
The natmod developer documentation is also updated to reflect the new
command line argument accepted by `mpy_ld.py` and the use cases for the
changes introduced by this commit.
Signed-off-by: Alessandro Gatti <a.gatti@frob.it>
This commit introduces an additional symbol resolution mechanism to the
natmod linking process. This allows the build scripts to look for required
symbols into selected libraries that are provided by the compiler
installation (libgcc and libm at the moment).
For example, using soft-float code in natmods, whilst technically possible,
was not an easy process and required some additional work to pull it off.
With this addition all the manual (and error-prone) operations have been
automated and folded into `tools/mpy_ld.py`.
Both newlib and picolibc toolchains are supported, albeit the latter may
require a bit of extra configuration depending on the environment the build
process runs on. Picolibc's soft-float functions aren't in libm - in fact
the shipped libm is nothing but a stub - but they are inside libc. This is
usually not a problem as these changes cater for that configuration quirk,
but on certain compilers the include paths used to find libraries in may
not be updated to take Picolibc's library directory into account. The bare
metal RISC-V compiler shipped with the CI OS image (GCC 10.2.0 on Ubuntu
22.04LTS) happens to exhibit this very problem.
To work around that for CI builds, the Picolibc libraries' path is
hardcoded in the Makefile directives used by the linker, but this can be
changed by setting the PICOLIBC_ROOT environment library when building
natmods.
Signed-off-by: Volodymyr Shymanskyy <vshymanskyi@gmail.com>
Co-authored-by: Alessandro Gatti <a.gatti@frob.it>
This commit adds support for RV32IMC native modules, as in embedding native
code into a self-contained MPY module and and make its exported functions
available to the MicroPython environment.
Signed-off-by: Alessandro Gatti <a.gatti@frob.it>
The STATIC macro was introduced a very long time ago in commit
d5df6cd44a. The original reason for this was
to have the option to define it to nothing so that all static functions
become global functions and therefore visible to certain debug tools, so
one could do function size comparison and other things.
This STATIC feature is rarely (if ever) used. And with the use of LTO and
heavy inline optimisation, analysing the size of individual functions when
they are not static is not a good representation of the size of code when
fully optimised.
So the macro does not have much use and it's simpler to just remove it.
Then you know exactly what it's doing. For example, newcomers don't have
to learn what the STATIC macro is and why it exists. Reading the code is
also less "loud" with a lowercase static.
One other minor point in favour of removing it, is that it stops bugs with
`STATIC inline`, which should always be `static inline`.
Methodology for this commit was:
1) git ls-files | egrep '\.[ch]$' | \
xargs sed -Ei "s/(^| )STATIC($| )/\1static\2/"
2) Do some manual cleanup in the diff by searching for the word STATIC in
comments and changing those back.
3) "git-grep STATIC docs/", manually fixed those cases.
4) "rg -t python STATIC", manually fixed codegen lines that used STATIC.
This work was funded through GitHub Sponsors.
Signed-off-by: Angus Gratton <angus@redyak.com.au>
The examples/natmod features0 and features1 examples now build and run on
ARMv6-M platforms. More complicated examples are not yet supported because
the compiler emits references to built-in functions like __aeabi_uidiv.
Signed-off-by: Damien George <damien@micropython.org>
