[PATCH 4/8] LoongArch: Support R_LARCH_B26 in modules

From: Xi Ruoyao
Date: Sat Aug 27 2022 - 13:56:13 EST


Binutils >= 2.40 uses R_LARCH_B26 for function calls with "bl"
instructions, instead of a pair of
R_LARCH_SOP_PUSH_PLT_PCREL and R_LARCH_SOP_POP_32_S_0_10_10_16_S2.
Handle R_LARCH_B26 in the module loader and create a PLT entry as
needed, so a modules can call functions in main kernel image if it's
built with Binutils >= 2.40.

Signed-off-by: Xi Ruoyao <xry111@xxxxxxxxxxx>
---
arch/loongarch/kernel/module-sections.c | 7 +++++-
arch/loongarch/kernel/module.c | 33 +++++++++++++++++++++++++
2 files changed, 39 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..e54df4717e4f 100644
--- a/arch/loongarch/kernel/module.c
+++ b/arch/loongarch/kernel/module.c
@@ -281,6 +281,38 @@ 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;
+}
+
/*
* reloc_handlers_rela() - Apply a particular relocation to a module
* @mod: the module to apply the reloc to
@@ -310,6 +342,7 @@ 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,
};

int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
--
2.37.0