casaroli opened a new pull request, #20814:
URL: https://github.com/apache/nuttx/pull/20814
## Summary
With LTO, arm, arm64 and risc-v set `CMAKE_LD` to gcc, and
`nuttx_add_application()` links each loadable module (`MODULE m`) with the
compiler driver. That link fails in two ways:
- The ELF link options of arm64 (`--gc-sections`, `-Bstatic`), risc-v
(`--oformat`) and arm (`-Bstatic`, and `--unresolved-symbols`, `--emit-relocs`
with `CONFIG_PIC`) are linker options. gcc stops with `unrecognized
command-line option '--gc-sections'`.
- The module objects and crt0 (`STARTUP_OBJS`) are compiled with `-flto`,
and the partial link (`-r`) cannot give the loader machine code. On arm the
link stops with `uses VFP register arguments, ... does not`, because gcc
compiles the LTO crt0 without the options of the target.
This PR gives the linker options with `-Wl,` when `CMAKE_LD` is gcc, as arm
already did for `--gc-sections`. An FDPIC module of arm is linked by the FDPIC
linker, so its options stay as they are. When LTO is on, the objects of a
loadable module and `STARTUP_OBJS` are compiled with `${NO_LTO}`. The image
keeps LTO.
## Impact
CMake builds with LTO and loadable modules: the modules link and load.
Builds without LTO, or with ld as `CMAKE_LD`, get the same options as before.
## Testing
`qemu-armv8a:nsh` (flat, CMake, Arm GNU 14.2 aarch64-none-elf, QEMU HVF),
`CONFIG_ELF`, `CONFIG_EXECFUNCS_SYSTEM_SYMTAB`, TLS test programs and `hello`
as `MODULE m`, loaded from a 9p share:
| | master | this PR |
|---|---|---|
| `CONFIG_LTO_FULL` | build fails: `unrecognized command-line option
'--gc-sections'` | tlsgroup, tls4, tlsmany, uctls, tlscxx PASS; `Hello,
World!!` |
| `CONFIG_LTO_NONE` | PASS | PASS |
With `CONFIG_LTO_FULL` the module link is `aarch64-none-elf-gcc ... -r
-Wl,--gc-sections -e _start -Wl,--defsym ...`, and crt0 and the module objects
are compiled with `-fno-lto`.
`mps2-an500:nsh` (CMake, arm-none-eabi 13.2, `CONFIG_LTO_FULL`): the modules
now link (`Tag_ABI_VFP_args: VFP registers`, `_start` defined). They could not
run: the CMake LTO link of the image itself fails, also on master (on master it
makes an empty image: `cannot find entry symbol __start`).
The tests ran with #20723 and #20807 for the TLS programs and
`get_environ_ptr`, and with apache/nuttx-apps#3883 for `hello`. "master" in the
table is master with these PRs.
`tools/checkpatch.sh -c -u -m -g` passes.
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