Swatantra-66 opened a new pull request, #20711:
URL: https://github.com/apache/nuttx/pull/20711
## Summary
Resolves the remaining open items in issue #19509 ("*[BUG] CMake build:
CONFIG_PIC gives ELF applications contradictory register flags and no -fpic,
and never reserves r10 in the base firmware*"):
Following PR #19600 which transitioned the PIC base register to `r9`, two
issues remained in the CMake build when `CONFIG_PIC=y`:
1. **Position-Independent Flags for ELF Applications:**
In `arch/arm/src/cmake/elf.cmake`, the `elseif(CONFIG_PIC)` branch
previously passed only `-mpic-register=r9`, causing the compiler warning:
`cc1: warning: '-mpic-register=' is useless without '-fpic'`
This patch passes `${PICFLAGS} -mpic-register=r9` to
`nuttx_elf_compile_options` (with fallback definition if `PICFLAGS` is
undefined), matching `CELFFLAGS` in `arch/arm/src/common/Toolchain.defs`.
2. **Reserve r9 in Base Firmware:**
Under `CONFIG_PIC`, base firmware routines could clobber `r9`. When
firmware calls back into module code (e.g. `qsort()` with a module comparator),
the module's data base was corrupted.
This patch adds `-ffixed-r9` to base firmware across GCC and Clang via:
`add_compile_options($<$<NOT:$<BOOL:$<TARGET_PROPERTY:ELF_BINARY>>>:-ffixed-r9>)`
in `arch/arm/src/cmake/gcc.cmake` and `arch/arm/src/cmake/clang.cmake`,
reserving `r9` for firmware while cleanly excluding all ELF targets.
3. **Mark `STARTUP_OBJS` as ELF Target:**
In `arch/arm/src/common/CMakeLists.txt`, set `ELF_BINARY TRUE` on
`STARTUP_OBJS` (`crt0.c`) so it receives PIC compilation options and is
excluded from `-ffixed-r9`.
## Impact
- **Build system:** Brings CMake ARM build under `CONFIG_PIC=y` into
functional parity with the Makefile build
(`arch/arm/src/common/Toolchain.defs`).
- **Compiler output:** Silences the `'-mpic-register=' is useless without
'-fpic'` warning when compiling `crt0.c` and ELF applications.
- **Runtime correctness:** Protects PIC module callbacks from data base
register corruption when invoked by base firmware routines.
- **Compatibility:** Strictly adheres to standard GCC and Clang
`-ffixed-reg` syntax.
## Testing
- Verified codebase style:
`./tools/checkpatch.sh -u`: 0 errors, 0 warnings.
- Target configuration:
`mps3-an547:picostest` (`CONFIG_PIC=y`).
Fixes #19509
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