jerpelea opened a new pull request, #20255:
URL: https://github.com/apache/nuttx/pull/20255
## Summary
A C++ module with a static object does not link. GCC registers each such
object's destructor with __cxa_atexit(dtor, obj, &__dso_handle), and
__dso_handle comes from crtbegin, which a module does not link:
hello++3.cxx:119: undefined reference to `__dso_handle'
It is reachable today with CONFIG_PIC, where a module is linked as an
executable and the symbol has to resolve. Without it the link is relocatable,
the symbol stays undefined and nothing complains until something makes it
resolve.
-fno-use-cxa-atexit registers the destructors with atexit() instead, which
puts them in .fini_array. That is also where libelf_uninit() looks for them
when the module is unloaded, so the flag that makes the link work is also the
flag that makes the destructors run.
The option goes wherever CXXELFFLAGS is defined, which is the architecture
Toolchain.defs and the boards that reassign it. The toolchains that are not
GCC or Clang are left alone: ceva, tricore, z16 and the z80 family.
The CMake build sets it once, next to where the architecture elf.cmake is
included. A generator expression keeps it off the C compiles, because the
option is valid for C++ alone and GCC warns about it otherwise, and the
compiler id gates it so that a toolchain which is neither GCC nor Clang does
not see it. It cannot go in the toolchain file itself: CMake reads that file
again inside try_compile, in a project that has not included the NuttX
extensions, so the call is an unknown command there.
Reproduced with apps/examples/elf on mps3-an547:picostest with CONFIG_PIC
enabled: hello++3 fails to link before and links after.
## Impact
RELEASE
## Testing
CI
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