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Date: Thu, 28 Jul 2022 20:41:29 +0800
From: Youling Tang <tangyouling@...ngson.cn>
To: Xi Ruoyao <xry111@...111.site>, loongarch@...ts.linux.dev
Cc: linux-kernel@...r.kernel.org, WANG Xuerui <kernel@...0n.name>,
Huacai Chen <chenhuacai@...nel.org>,
Jinyang He <hejinyang@...ngson.cn>
Subject: Re: [PATCH v2 4/4] LoongArch: Support modules with new relocation
types
On 07/28/2022 08:04 PM, Xi Ruoyao wrote:
> If GAS 2.40 and/or GCC 13 is used to build the kernel, the modules will
> contain R_LARCH_B26, R_LARCH_PCALA_HI20, R_LARCH_PCALA_LO12,
> R_LARCH_GOT_PC_HI20, and R_LARCH_GOT_PC_LO12 relocations. Support them
> in the module loader to allow a kernel built with latest toolchain
> capable to load the modules.
>
> Signed-off-by: Xi Ruoyao <xry111@...111.site>
> ---
> arch/loongarch/include/asm/elf.h | 37 +++++++++++
> arch/loongarch/kernel/module-sections.c | 12 +++-
> arch/loongarch/kernel/module.c | 83 +++++++++++++++++++++++++
> 3 files changed, 130 insertions(+), 2 deletions(-)
>
> diff --git a/arch/loongarch/include/asm/elf.h b/arch/loongarch/include/asm/elf.h
> index 5f3ff4781fda..7af0cebf28d7 100644
> --- a/arch/loongarch/include/asm/elf.h
> +++ b/arch/loongarch/include/asm/elf.h
> @@ -74,6 +74,43 @@
> #define R_LARCH_SUB64 56
> #define R_LARCH_GNU_VTINHERIT 57
> #define R_LARCH_GNU_VTENTRY 58
> +#define R_LARCH_B16 64
> +#define R_LARCH_B21 65
> +#define R_LARCH_B26 66
> +#define R_LARCH_ABS_HI20 67
> +#define R_LARCH_ABS_LO12 68
> +#define R_LARCH_ABS64_LO20 69
> +#define R_LARCH_ABS64_HI12 70
> +#define R_LARCH_PCALA_HI20 71
> +#define R_LARCH_PCALA_LO12 72
> +#define R_LARCH_PCALA64_LO20 73
> +#define R_LARCH_PCALA64_HI12 74
> +#define R_LARCH_GOT_PC_HI20 75
> +#define R_LARCH_GOT_PC_LO12 76
> +#define R_LARCH_GOT64_PC_LO20 77
> +#define R_LARCH_GOT64_PC_HI12 78
> +#define R_LARCH_GOT_HI20 79
> +#define R_LARCH_GOT_LO12 80
> +#define R_LARCH_GOT64_LO20 81
> +#define R_LARCH_GOT64_HI12 82
> +#define R_LARCH_TLS_LE_HI20 83
> +#define R_LARCH_TLS_LE_LO12 84
> +#define R_LARCH_TLS_LE64_LO20 85
> +#define R_LARCH_TLS_LE64_HI12 86
> +#define R_LARCH_TLS_IE_PC_HI20 87
> +#define R_LARCH_TLS_IE_PC_LO12 88
> +#define R_LARCH_TLS_IE64_PC_LO20 89
> +#define R_LARCH_TLS_IE64_PC_HI12 90
> +#define R_LARCH_TLS_IE_HI20 91
> +#define R_LARCH_TLS_IE_LO12 92
> +#define R_LARCH_TLS_IE64_LO20 93
> +#define R_LARCH_TLS_IE64_HI12 94
> +#define R_LARCH_TLS_LD_PC_HI20 95
> +#define R_LARCH_TLS_LD_HI20 96
> +#define R_LARCH_TLS_GD_PC_HI20 97
> +#define R_LARCH_TLS_GD_HI20 98
> +#define R_LARCH_32_PCREL 99
> +#define R_LARCH_RELAX 100
>
> #ifndef ELF_ARCH
>
> diff --git a/arch/loongarch/kernel/module-sections.c b/arch/loongarch/kernel/module-sections.c
> index 36a77771d18c..8c0e4ad048cc 100644
> --- a/arch/loongarch/kernel/module-sections.c
> +++ b/arch/loongarch/kernel/module-sections.c
> @@ -76,12 +76,20 @@ static void count_max_entries(Elf_Rela *relas, int num,
>
> 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)++;
> - } else if (type == R_LARCH_SOP_PUSH_GPREL)
> + break;
> + case R_LARCH_SOP_PUSH_GPREL:
> + case R_LARCH_GOT_PC_HI20:
> if (!duplicate_rela(relas, i))
> (*gots)++;
> + break;
> + default:
> + /* Do nothing. */
> + }
> }
> }
>
> diff --git a/arch/loongarch/kernel/module.c b/arch/loongarch/kernel/module.c
> index 3ac4fbb5f109..8954ac24d4ab 100644
> --- a/arch/loongarch/kernel/module.c
> +++ b/arch/loongarch/kernel/module.c
> @@ -291,6 +291,84 @@ 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;
> +
> + 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 (!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;
> + }
> +
> + 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;
> + }
Unaligned is handled more efficiently before overflow checking, while
being consistent with apply_r_larch_sop_imm_field.
> +
> + *location &= ~(u32)0x3ffffff;
> + *location |= (offset >> 18) & 0x3ff;
> + *location |= ((offset >> 2) & 0xffff) << 10;
It may be better to use the loongarch_instruction format to modify the
immediate field of the instruction, similar to the following:
union loongarch_instruction *insn = (union loongarch_instruction *)location;
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_hi20(struct module *mod, u32 *location,
> + Elf_Addr v, s64 *rela_stack, size_t *rela_stack_top,
> + unsigned int type)
> +{
> + ptrdiff_t offset = (void *)((v + 0x800) & ~0xfff) -
> + (void *)((Elf_Addr)location & ~0xfff);
> +
> + if (!signed_imm_check(offset, 32)) {
> + pr_err("module %s: PCALA offset = 0x%llx does not fit in 32-bit signed and is unsupported by kernel! dangerous %s (%u) relocation\n",
> + mod->name, (long long)offset, __func__, type);
> + return -ENOEXEC;
> + }
> +
> + *location &= ~((u32)0xfffff << 5);
> + *location |= ((offset >> 12) & 0xfffff) << 5;
Ditto.
> + return 0;
> +}
> +
> +static int apply_r_larch_got_pc_hi20(struct module *mod, u32 *location,
> + Elf_Addr v, s64 *rela_stack, size_t *rela_stack_top,
> + unsigned int type)
> +{
> + Elf_Addr got = module_emit_got_entry(mod, v);
> +
> + return apply_r_larch_pcala_hi20(mod, location, got, rela_stack,
> + rela_stack_top, type);
> +}
> +
> +static int apply_r_larch_pcala_lo12(struct module *mod, u32 *location,
> + Elf_Addr v, s64 *rela_stack, size_t *rela_stack_top,
> + unsigned int type)
> +{
> + *location &= ~((u32)0xfff << 10);
> + *location |= ((u32)v & 0xfff) << 10;
Ditto.
Thanks,
Youling
> + return 0;
> +}
> +
> +static int apply_r_larch_got_pc_lo12(struct module *mod, u32 *location,
> + Elf_Addr v, s64 *rela_stack, size_t *rela_stack_top,
> + unsigned int type)
> +{
> + Elf_Addr got = module_emit_got_entry(mod, v);
> +
> + return apply_r_larch_pcala_lo12(mod, location, got, rela_stack,
> + rela_stack_top, type);
> +}
> +
> /*
> * reloc_handlers_rela() - Apply a particular relocation to a module
> * @mod: the module to apply the reloc to
> @@ -321,6 +399,11 @@ 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] = apply_r_larch_pcala_hi20,
> + [R_LARCH_PCALA_LO12] = apply_r_larch_pcala_lo12,
> + [R_LARCH_GOT_PC_HI20] = apply_r_larch_got_pc_hi20,
> + [R_LARCH_GOT_PC_LO12] = apply_r_larch_got_pc_lo12,
> };
>
> int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
>
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