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ARM PIC has used r10 as the base register, but the tree has never been consistent about it. Toolchain.defs gives CONFIG_BUILD_PIC -mpic-register=r9 and CONFIG_PIC -mpic-register=r10, twenty-five lines apart, and arm_initialstate.c sets REG_R9 from inline assembly under one and REG_PIC under the other, with a comment reading "Set the PIC base register (probably R10)". This settles it on r9 for all of PIC: NXFLAT, ELF PIC and CONFIG_BUILD_PIC alike. r9 is the right choice rather than an arbitrary one. It is the AAPCS platform register, the "static base", and it is what GCC itself picks for -msingle-pic-base on an EABI target; r10 is the non-EABI default. It also removes a combination that cannot build today. Stack checking adds -ffixed-r10 in armv7-m/Toolchain.defs and armv8-m/Toolchain.defs, while CONFIG_PIC adds -mpic-register=r10, and GCC rejects the pair with "unable to use 'r10' for PIC register". The comment above REG_PIC has always said the register "can be R9 if stack checking is enabled", but the definition was unconditionally REG_R10, so it would have named the wrong register even had the build succeeded. The thunk generator moves with the firmware. NXFLAT import stubs had the register baked in as "add ip,ip,sl", so a module built for r9 would load and then branch to a wild address on its first call out. The stubs now come from NXFLAT_PIC_REG in the in-tree tool, which is built only when CONFIG_NXFLAT is set, following the CONFIG_BOARD_ETC_ROMFS_PASSWD_ENABLE precedent in tools/Unix.mk. That leaves modules built before this change, and they are the reason for the ABI marker. The NXFLAT header cannot carry a version: h_magic is written by ldnxflat, which is GPL, derived from elf2flt, and stays out of this repository, so it can never be changed in step with the loader. The import table can, because both of its ends are in-tree -- mknxflat emits it and nxflat_bindimports() reads it -- and ldnxflat passes it through untouched. So every module now imports __nxflat_abi_v2, the base firmware defines it, and a module that does not import it is refused. Making the marker a real exported symbol rather than a name the loader special-cases is what keeps it out of the build system's way: a board's symbol table picks it up exactly as it picks up printf, so mksymtab.sh and its equivalents need no change. It also gives the reverse direction a diagnosis for free -- a module built against a newer ABI than its firmware fails with "Exported symbol __nxflat_abi_v2 not found". Most of the remaining churn is boards restating a default. ARCHPICFLAGS is a "?=" default so that a board only speaks up when it differs, and twenty-six were assigning the value the default already had. MKNXFLAT gets the same treatment: thirteen boards named the same tool, and the only thing that varies is ARM versus Thumb-2, which falls out of CONFIG_ARM_THUMB. LDNXFLAT gains a default too -- it stays an out-of-tree PATH lookup, but naming it centrally fixes boards that never assigned it, where it expanded to nothing and handed make a recipe beginning "-e", whose leading dash make ate as "ignore errors". The non-ARM boards carrying -mpic-register=r10 lose it: it is an ARM-only option, reachable only through CPICFLAGS, which is only used to build NXFLAT modules, and no non-ARM board enables NXFLAT. Boards keep nothing about PIC flags any more. ARCHPICFLAGS was set by sixty-three of them and only ever fed CPICFLAGS, which is only used to build NXFLAT modules; no board outside arch/arm enables NXFLAT, so every non-ARM copy was setting a variable nothing read. Those are removed rather than moved somewhere more central, which would only make dead text look load-bearing. LDNXFLAT goes the same way as MKNXFLAT, for the same reason: thirteen boards named the same tool that Toolchain.defs now names once. One of them was not merely redundant. am67/t3-gem-o1 asked for "-mpic-register=r10 -ffixed-r10", which GCC refuses outright with "unable to use 'r10' for PIC register" -- the very combination the filter-out machinery in Toolchain.defs exists to prevent. It has survived because that board does not build NXFLAT modules, so the flags are never handed to a compiler. Renaming the register would have carried the fault forward unchanged, so the line goes. Tested on lm3s6965-ek:qemu-nxflat under QEMU, configured and built with no overrides. The nxflat example runs the errno, hello and struct modules with output identical to the same config built from master. Built with the old out-of-tree thunk generator instead, the same firmware refuses all three with ENOEXEC rather than locking up in a HardFault, which is what this change is for. mps3-an547:picostest, which is CONFIG_PIC without CONFIG_NXFLAT, builds clean and does not build the thunk generator. The .def files pick up two cosmetic changes here alongside the register: a "Dyanamic" typo that codespell rejects, and a reworded comment in each thunk_*.c. Neither appears in the emitted thunk -- both are in C comments -- so the generated text is still what the upstream tool produces, modulo the register itself. BREAKING CHANGE: ARM PIC moves from r10 to r9. An NXFLAT module built before this change has r10 baked into its import stubs and will not run against a firmware carrying it; the two cannot be mixed. The module is refused with ENOEXEC rather than branching to a wild address, by way of the __nxflat_abi_v2 marker described below. Quick fix: rebuild the module against this tree. Its source needs no change. A board that reserved r10 by hand, or that assigned ARCHPICFLAGS or MKNXFLAT to restate a default, should drop those assignments; nothing else is affected, and CONFIG_PIC without CONFIG_NXFLAT needs no action. Assisted-by: Claude Opus 5 (1M context) <noreply@anthropic.com> Signed-off-by: Marco Casaroli <marco.casaroli@gmail.com> |
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