casaroli opened a new pull request, #20360:
URL: https://github.com/apache/nuttx/pull/20360
## Summary
Part of the FDPIC series. `[5.5/10]` #19940 taught the ELF module path what
an FDPIC object is, so an application built as a module gets `-mfdpic -fPIC`
and the `arm-uclinuxfdpiceabi` linker, and comes out a shared object the loader
can bind.
The loadable module path was left behind. `apps/Application.mk` reaches it
with `DYNLIB = y`, `apps/Library.mk` builds every shared library with it, and
it is still a `-r` partial link with the stock linker. Such an object has no
dynamic section, so nothing can bind an import to it, and there is no way to
build a library an FDPIC module can call.
So `CMODULEFLAGS` and `CXXMODULEFLAGS` gain the same compiler flags, and
`LDMODULEFLAGS` links a shared object rather than a partial one. The entry
point stays with the caller, because a module is entered at `_start` while a
library is only ever called into.
`CXXMODULEFLAGS` is defined here for the first time. `apps/Library.mk`
compiles every C++ source of a shared library with it and no architecture ever
defined it, so those sources were compiled with no architecture flags at all.
apache/nuttx-apps#3762 is the first user: its module fixtures stop
hand-rolling the link and use these variables.
## Impact
Everything else is under `CONFIG_FDPIC`, which defaults off and is
selectable only where `ARCH_HAVE_ELF_FDPIC` is set.
`CXXMODULEFLAGS` replaces nothing, since it was empty.
## Testing
Compiled and linked a library with the variables this patch produces, taken
from a `pimoroni-pico-2-plus` tree configured with `CONFIG_FDPIC`:
```
$ arm-uclinuxfdpiceabi-readelf -dh libcounter.so
OS/ABI: ARM FDPIC
Type: DYN (Shared object file)
Entry point: 0x0
0x0e (SONAME) Library soname: [libcounter.so]
```
Two `PT_LOAD` segments, `R E` and `RW`, as an FDPIC object needs.
`tools/checkpatch.sh -c -u -m -g` passes.
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