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Date: Mon, 29 Aug 2022 23:08:03 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Xi Ruoyao <xry111@...111.site>
Cc: loongarch@...ts.linux.dev, LKML <linux-kernel@...r.kernel.org>,
WANG Xuerui <kernel@...0n.name>,
Youling Tang <tangyouling@...ngson.cn>,
Jinyang He <hejinyang@...ngson.cn>
Subject: Re: [PATCH v6 5/6] LoongArch: Support PC-relative relocations in modules
Hi, Ruoyao,
On Mon, Aug 29, 2022 at 9:35 PM Xi Ruoyao <xry111@...111.site> wrote:
>
> Binutils >= 2.40 uses R_LARCH_B26 instead of R_LARCH_SOP_PUSH_PLT_PCREL,
> and R_LARCH_PCALA* instead of R_LARCH_SOP_PUSH_PCREL.
>
> Handle R_LARCH_B26 and R_LARCH_PCALA* in the module loader. For
> R_LARCH_B26, also create a PLT entry as needed.
>
> Signed-off-by: Xi Ruoyao <xry111@...111.site>
> ---
> arch/loongarch/kernel/module-sections.c | 7 ++-
> arch/loongarch/kernel/module.c | 75 +++++++++++++++++++++++++
> 2 files changed, 81 insertions(+), 1 deletion(-)
>
> diff --git a/arch/loongarch/kernel/module-sections.c b/arch/loongarch/kernel/module-sections.c
> index 6d498288977d..c67b9cb220eb 100644
> --- a/arch/loongarch/kernel/module-sections.c
> +++ b/arch/loongarch/kernel/module-sections.c
> @@ -56,9 +56,14 @@ static void count_max_entries(Elf_Rela *relas, int num, unsigned int *plts)
>
> for (i = 0; i < num; i++) {
> type = ELF_R_TYPE(relas[i].r_info);
> - if (type == R_LARCH_SOP_PUSH_PLT_PCREL) {
> + switch (type) {
> + case R_LARCH_SOP_PUSH_PLT_PCREL:
> + case R_LARCH_B26:
> if (!duplicate_rela(relas, i))
> (*plts)++;
> + break;
> + default:
> + /* Do nothing. */
> }
> }
> }
> diff --git a/arch/loongarch/kernel/module.c b/arch/loongarch/kernel/module.c
> index 755d91ef8d85..0024bc6c4af1 100644
> --- a/arch/loongarch/kernel/module.c
> +++ b/arch/loongarch/kernel/module.c
> @@ -281,6 +281,79 @@ static int apply_r_larch_add_sub(struct module *mod, u32 *location, Elf_Addr v,
> }
> }
>
> +static int apply_r_larch_b26(struct module *mod, u32 *location, Elf_Addr v,
> + s64 *rela_stack, size_t *rela_stack_top, unsigned int type)
> +{
> + ptrdiff_t offset = (void *)v - (void *)location;
> + union loongarch_instruction *insn = (union loongarch_instruction *)location;
> +
> + if (offset >= SZ_128M)
> + v = module_emit_plt_entry(mod, v);
> +
> + if (offset < -SZ_128M)
> + v = module_emit_plt_entry(mod, v);
> +
> + offset = (void *)v - (void *)location;
> +
> + if (offset & 3) {
> + pr_err("module %s: jump offset = 0x%llx unaligned! dangerous R_LARCH_B26 (%u) relocation\n",
> + mod->name, (long long)offset, type);
> + return -ENOEXEC;
> + }
> +
> + if (!signed_imm_check(offset, 28)) {
> + pr_err("module %s: jump offset = 0x%llx overflow! dangerous R_LARCH_B26 (%u) relocation\n",
> + mod->name, (long long)offset, type);
> + return -ENOEXEC;
> + }
> +
> + offset >>= 2;
> + insn->reg0i26_format.immediate_l = offset & 0xffff;
> + insn->reg0i26_format.immediate_h = (offset >> 16) & 0x3ff;
> + return 0;
> +}
> +
> +static int apply_r_larch_pcala(struct module *mod, u32 *location, Elf_Addr v,
> + s64 *rela_stack, size_t *rela_stack_top, unsigned int type)
> +{
> + union loongarch_instruction *insn = (union loongarch_instruction *)location;
> + /* Use s32 for a sign-extension deliberately. */
> + s32 offset_hi20 = (void *)((v + 0x800) & ~0xfff) -
> + (void *)((Elf_Addr)location & ~0xfff);
> + Elf_Addr anchor = (((Elf_Addr)location) & ~0xfff) + offset_hi20;
> + ptrdiff_t offset_rem = (void *)v - (void *)anchor;
> +
> + switch (type) {
> + case R_LARCH_PCALA_HI20:
> + v = offset_hi20 >> 12;
> + break;
> + case R_LARCH_PCALA64_LO20:
> + v = offset_rem >> 32;
> + break;
> + case R_LARCH_PCALA64_HI12:
> + v = offset_rem >> 52;
> + break;
> + default:
> + /* Do nothing. */
> + }
> +
> + switch (type) {
> + case R_LARCH_PCALA_HI20:
> + case R_LARCH_PCALA64_LO20:
> + insn->reg1i20_format.immediate = v & 0xfffff;
> + break;
> + case R_LARCH_PCALA_LO12:
> + case R_LARCH_PCALA64_HI12:
> + insn->reg2i12_format.immediate = v & 0xfff;
> + break;
> + default:
> + pr_err("%s: Unsupport relocation type %u\n", mod->name, type);
> + return -EINVAL;
> + }
Can we merge the two switch here?
Huacai
> +
> + return 0;
> +}
> +
> /*
> * reloc_handlers_rela() - Apply a particular relocation to a module
> * @mod: the module to apply the reloc to
> @@ -310,6 +383,8 @@ static reloc_rela_handler reloc_rela_handlers[] = {
> [R_LARCH_SOP_SUB ... R_LARCH_SOP_IF_ELSE] = apply_r_larch_sop,
> [R_LARCH_SOP_POP_32_S_10_5 ... R_LARCH_SOP_POP_32_U] = apply_r_larch_sop_imm_field,
> [R_LARCH_ADD32 ... R_LARCH_SUB64] = apply_r_larch_add_sub,
> + [R_LARCH_B26] = apply_r_larch_b26,
> + [R_LARCH_PCALA_HI20...R_LARCH_PCALA64_HI12] = apply_r_larch_pcala,
> };
>
> int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
> --
> 2.37.0
>
>
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