Re: [PATCH v7 0/5] LoongArch: Support toolchain with new relocation types

[Huacai Chen]

Hi, Ruoyao,

Thank you for your contribution, this whole series will be queued for
6.1. Though lkp reported some warnings, I will fix them myself.

Huacai

On Tue, Aug 30, 2022 at 6:48 PM Xi Ruoyao <xry111@xxxxxxxxxxx> wrote:
>
> The version 2.00 of LoongArch ELF ABI specification introduced new
> relocation types, and the development tree of Binutils and GCC has
> started to use them.  If the kernel is built with the latest snapshot of
> Binutils or GCC, it will fail to load the modules because of unrecognized
> relocation types in modules.
>
> Add support for GOT and new relocation types for the module loader, so
> the kernel (with modules) can be built with the "normal" code model and
> function properly.
>
> This series does not break the compatibility with old toolchain using
> stack-based relocation types, so with the patches applied the kernel can
> be be built with both old and new toolchains.  But, the combination of
> "new" Binutils and "old" GCC is not supported.
>
> Tested by building the kernel with the following combinations:
>
> - GCC 12 and Binutils 2.39
> - GCC trunk and Binutils trunk
>
> and running the builds with 35 in-tree modules loaded, and loading one
> module with 20 GOT loads and a per-CPU variable (loaded addresses
> verified by comparing with /proc/kallsyms).
>
> Changes from v6 to v7:
>
> - Simplify apply_r_larch_pcala.
> - Remove a build check only for excluding early GCC 13 dev snapshots.
> - Squash model attribute addition into the previous patch.
> - Retain "-fplt".
>
> Changes from v5 to v6:
>
> - Restore version number.
> - Rename CONFIG_CC_HAS_EXPLICIT_RELOCS to CONFIG_AS_HAS_EXPLICIT_RELOCS.
>   It now only checks assembler.
> - No longer support "old GCC with new Binutils", so R_LARCH_ABS* is
>   dropped.
>   - "Old GCC with old Binutils" is still supported until Arnd ack.
>   - "New GCC with old Binutils" is still supported as it does not
>     require additional code.
> - Remove "cc-option" around "-mexplicit-relocs".  For unsupported
>   "old GCC with new Binutils" combination, forcing -mexplicit-relocs
>   makes assembling fail, instead of silently producing unloadable
>   modules.
> - Move the error report for "lacking model attribute" into Makefile.
> - Squash the two patches for R_LARCH_B26 and R_LARCH_PCALA* into one.
>
> Changes from v4 to v5 ("v5" missed in the subject):
>
> - Change subject.
> - Introduce CONFIG_CC_HAS_EXPLICIT_RELOCS.
> - Retain -Wa,-mla-* options for old toolchains
>   (!CONFIG_CC_HAS_EXPLICIT_RELOCS).
> - Use __attribute__((model("extreme"))) in PER_CPU_ATTRIBUTES, to fix
>   a breakage with per-CPU variables defined in modules.
> - Handle R_LARCH_PCALA64_{HI12,LO12} for extreme model.
> - Handle R_LARCH_ABS* for "old GCC with new Binutils".
> - Separate the last patch into more small patches.
> - Avoid BUG_ON() for the handling of GOT.
>
> Changes from v3 to v4:
>
> - No code change.  Reword the commit message of the 3rd patch again
>   based on suggestion from Huacai.
>
> Changes from v2 to v3:
>
> - Use `union loongarch_instruction` instead of explicit bit shifts
>   applying the relocation.  Suggested by Youling.
> - For R_LARCH_B26, move the alignment check before the range check to be
>   consistent with stack pop relocations.  Suggested by Youling.
> - Reword the commit message of the 3rd patch.  Suggested by Huacai.
>
> Changes from v1 to v2:
>
> - Fix a stupid programming error (confusion between the number of PLT
>   entries and the number of GOT entries).  (Bug spotted by Youling).
> - Synthesize the _GLOBAL_OFFSET_TABLE_ symbol with module.lds, instead
>   of faking it at runtime.  The 3rd patch from V1 is now merged into
>   the 1st patch because it would be a one-line change.  (Suggested by
>   Jinyang).
> - Keep reloc_rela_handlers[] ordered by the relocation type ID.
>   (Suggested by Youling).
> - Remove -fplt along with -Wa,-mla-* options because it's the default.
>   (Suggested by Youling).
>
> Xi Ruoyao (5):
>   LoongArch: Add CONFIG_AS_HAS_EXPLICIT_RELOCS
>   LoongArch: Adjust symbol addressing for CONFIG_AS_HAS_EXPLICIT_RELOCS
>   LoongArch: Define ELF relocation types added in v2.00 ABI
>   LoongArch: Support PC-relative relocations in modules
>   LoongArch: Support R_LARCH_GOT_PC* in modules
>
>  arch/loongarch/Kconfig                  |  3 +
>  arch/loongarch/Makefile                 | 17 +++++
>  arch/loongarch/include/asm/elf.h        | 37 ++++++++++
>  arch/loongarch/include/asm/module.h     | 23 ++++++
>  arch/loongarch/include/asm/module.lds.h |  1 +
>  arch/loongarch/include/asm/percpu.h     |  8 +++
>  arch/loongarch/kernel/head.S            | 10 +--
>  arch/loongarch/kernel/module-sections.c | 56 +++++++++++++--
>  arch/loongarch/kernel/module.c          | 93 ++++++++++++++++++++++++-
>  9 files changed, 238 insertions(+), 10 deletions(-)
>
> --
> 2.37.0
>