Re: [PATCH v4 0/4] LoongArch: Support new relocation types

[Youling Tang <tangyouling@loongson.cn>]

Hi, Ruoyao

Tested this series of patches v3 on a CLFS 5.5 system, using the new
cross toolchain,
$ dmesg | head
[    0.000000] Linux version 5.19.0-rc7new-toolchain+ (loongson@linux) 
(loongarch64-unknown-linux-gnu-gcc (GCC) 13.0.0 20220726 (experimental) 
[master revision 
cf7eac5805e:1e0611b64d8:3fb68f2e666d9de7e0326af9f43b12c9e98f19a6], GNU 
ld (GNU Binutils) 2.39.50.20220726) #1 SMP PREEMPT Fri Jul 29 05:24:15 
EDT 2022

Relocation error when manually loading nf_tables.ko module,
$ sudo modprobe nf_tables
odprobe: ERROR: could not insert 'nf_tables': Exec format error

$ dmesg
[   61.506737] kmod: module nf_tables: PCALA offset = 0x90007ffffed8c000 
does not fit in 32-bit signed and is unsupported by kernel! dangerous 
apply_r_larch_pcala_hi20 (71) relocation

Do you have the same problem over there?

Thanks,
Youling

On 07/29/2022 04:38 PM, Xi Ruoyao 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.
>
> Tested by building the kernel with both Binutils & GCC master branch and
> my system Binutils & GCC (without new relocation type support), running
> both the builds with 35 in-tree modules loaded, and loading one module
> with 20 GOT loads (loaded addresses verified by comparing with
> /proc/kallsyms).
>
> 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 (4):
>   LoongArch: Add section of GOT for kernel module
>   LoongArch: Support R_LARCH_SOP_PUSH_GPREL relocation type in kernel
>     module
>   LoongArch: Remove -fplt and -Wa,-mla-* from CFLAGS
>   LoongArch: Support modules with new relocation types
>
>  arch/loongarch/Makefile                 |  4 --
>  arch/loongarch/include/asm/elf.h        | 37 ++++++++++
>  arch/loongarch/include/asm/module.h     | 23 ++++++
>  arch/loongarch/include/asm/module.lds.h |  1 +
>  arch/loongarch/kernel/head.S            | 10 +--
>  arch/loongarch/kernel/module-sections.c | 51 +++++++++++--
>  arch/loongarch/kernel/module.c          | 96 +++++++++++++++++++++++++
>  7 files changed, 209 insertions(+), 13 deletions(-)
>