[PATCH v2 1/2] riscv: Add remaining module relocations

From: Charlie Jenkins
Date: Fri Oct 06 2023 - 20:41:33 EST

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Add all final module relocations and add error logs explaining the ones
that are not supported.

Signed-off-by: Charlie Jenkins <charlie@xxxxxxxxxxxx>
---
arch/riscv/include/uapi/asm/elf.h | 6 +-
arch/riscv/kernel/module.c | 247 ++++++++++++++++++++++++++++++++++----
2 files changed, 227 insertions(+), 26 deletions(-)

diff --git a/arch/riscv/include/uapi/asm/elf.h b/arch/riscv/include/uapi/asm/elf.h
index d696d6610231..a9307a1c9ceb 100644
--- a/arch/riscv/include/uapi/asm/elf.h
+++ b/arch/riscv/include/uapi/asm/elf.h
@@ -49,6 +49,7 @@ typedef union __riscv_fp_state elf_fpregset_t;
#define R_RISCV_TLS_DTPREL64 9
#define R_RISCV_TLS_TPREL32 10
#define R_RISCV_TLS_TPREL64 11
+#define R_RISCV_IRELATIVE 58

/* Relocation types not used by the dynamic linker */
#define R_RISCV_BRANCH 16
@@ -81,7 +82,7 @@ typedef union __riscv_fp_state elf_fpregset_t;
#define R_RISCV_ALIGN 43
#define R_RISCV_RVC_BRANCH 44
#define R_RISCV_RVC_JUMP 45
-#define R_RISCV_LUI 46
+#define R_RISCV_RVC_LUI 46
#define R_RISCV_GPREL_I 47
#define R_RISCV_GPREL_S 48
#define R_RISCV_TPREL_I 49
@@ -93,6 +94,9 @@ typedef union __riscv_fp_state elf_fpregset_t;
#define R_RISCV_SET16 55
#define R_RISCV_SET32 56
#define R_RISCV_32_PCREL 57
+#define R_RISCV_PLT32 59
+#define R_RISCV_SET_ULEB128 60
+#define R_RISCV_SUB_ULEB128 61

#endif /* _UAPI_ASM_RISCV_ELF_H */
diff --git a/arch/riscv/kernel/module.c b/arch/riscv/kernel/module.c
index 7c651d55fcbd..61d5cdbe609d 100644
--- a/arch/riscv/kernel/module.c
+++ b/arch/riscv/kernel/module.c
@@ -7,6 +7,7 @@
#include <linux/elf.h>
#include <linux/err.h>
#include <linux/errno.h>
+#include <linux/kernel.h>
#include <linux/moduleloader.h>
#include <linux/vmalloc.h>
#include <linux/sizes.h>
@@ -253,6 +254,30 @@ static int apply_r_riscv_call_rela(struct module *me, u32 *location,
return 0;
}

+static int apply_r_riscv_rvc_lui_rela(struct module *me, u32 *location,
+ Elf_Addr v)
+{
+ // Get high 6 bits of 18 bit absolute address
+ s32 imm = ((s32)v + 0x800) >> 12;
+
+ if (v != sign_extend32(v, 6)) {
+ pr_err("%s: target %016llx can not be addressed by the 6-bit offset from PC = %p\n",
+ me->name, (long long)v, location);
+ return -EINVAL;
+ }
+
+ if (imm == 0) {
+ // imm = 0 is invalid for c.lui, convert to c.li
+ *location = (*location & 0x0F83) | 0x4000;
+ } else {
+ u16 imm17 = ((((s32)v + 0x800) & 0x20000) >> (17 - 12));
+ u16 imm16_12 = ((((s32)v + 0x800) & 0x1f000) >> (12 - 2));
+ *location = (*location & 0xef83) | imm17 | imm16_12;
+ }
+
+ return 0;
+}
+
static int apply_r_riscv_relax_rela(struct module *me, u32 *location,
Elf_Addr v)
{
@@ -268,6 +293,12 @@ static int apply_r_riscv_align_rela(struct module *me, u32 *location,
return -EINVAL;
}

+static int apply_r_riscv_add8_rela(struct module *me, u32 *location, Elf_Addr v)
+{
+ *(u8 *)location += (u8)v;
+ return 0;
+}
+
static int apply_r_riscv_add16_rela(struct module *me, u32 *location,
Elf_Addr v)
{
@@ -289,6 +320,12 @@ static int apply_r_riscv_add64_rela(struct module *me, u32 *location,
return 0;
}

+static int apply_r_riscv_sub8_rela(struct module *me, u32 *location, Elf_Addr v)
+{
+ *(u8 *)location -= (u8)v;
+ return 0;
+}
+
static int apply_r_riscv_sub16_rela(struct module *me, u32 *location,
Elf_Addr v)
{
@@ -310,31 +347,150 @@ static int apply_r_riscv_sub64_rela(struct module *me, u32 *location,
return 0;
}

-static int (*reloc_handlers_rela[]) (struct module *me, u32 *location,
- Elf_Addr v) = {
- [R_RISCV_32] = apply_r_riscv_32_rela,
- [R_RISCV_64] = apply_r_riscv_64_rela,
- [R_RISCV_BRANCH] = apply_r_riscv_branch_rela,
- [R_RISCV_JAL] = apply_r_riscv_jal_rela,
- [R_RISCV_RVC_BRANCH] = apply_r_riscv_rvc_branch_rela,
- [R_RISCV_RVC_JUMP] = apply_r_riscv_rvc_jump_rela,
- [R_RISCV_PCREL_HI20] = apply_r_riscv_pcrel_hi20_rela,
- [R_RISCV_PCREL_LO12_I] = apply_r_riscv_pcrel_lo12_i_rela,
- [R_RISCV_PCREL_LO12_S] = apply_r_riscv_pcrel_lo12_s_rela,
- [R_RISCV_HI20] = apply_r_riscv_hi20_rela,
- [R_RISCV_LO12_I] = apply_r_riscv_lo12_i_rela,
- [R_RISCV_LO12_S] = apply_r_riscv_lo12_s_rela,
- [R_RISCV_GOT_HI20] = apply_r_riscv_got_hi20_rela,
- [R_RISCV_CALL_PLT] = apply_r_riscv_call_plt_rela,
- [R_RISCV_CALL] = apply_r_riscv_call_rela,
- [R_RISCV_RELAX] = apply_r_riscv_relax_rela,
- [R_RISCV_ALIGN] = apply_r_riscv_align_rela,
- [R_RISCV_ADD16] = apply_r_riscv_add16_rela,
- [R_RISCV_ADD32] = apply_r_riscv_add32_rela,
- [R_RISCV_ADD64] = apply_r_riscv_add64_rela,
- [R_RISCV_SUB16] = apply_r_riscv_sub16_rela,
- [R_RISCV_SUB32] = apply_r_riscv_sub32_rela,
- [R_RISCV_SUB64] = apply_r_riscv_sub64_rela,
+static int dynamic_linking_not_supported(struct module *me, u32 *location,
+ Elf_Addr v)
+{
+ pr_err("%s: Dynamic linking not supported in kernel modules PC = %p\n",
+ me->name, location);
+ return -EINVAL;
+}
+
+static int tls_not_supported(struct module *me, u32 *location, Elf_Addr v)
+{
+ pr_err("%s: Thread local storage not supported in kernel modules PC = %p\n",
+ me->name, location);
+ return -EINVAL;
+}
+
+static int apply_r_riscv_sub6_rela(struct module *me, u32 *location, Elf_Addr v)
+{
+ *(u8 *)location -= (u8)v & 0x3F;
+ return 0;
+}
+
+static int apply_r_riscv_set6_rela(struct module *me, u32 *location, Elf_Addr v)
+{
+ *(u8 *)location = (*(u8 *)location & 0xc0) | ((u8)v & 0x3F);
+ return 0;
+}
+
+static int apply_r_riscv_set8_rela(struct module *me, u32 *location, Elf_Addr v)
+{
+ *(u8 *)location = (u8)v;
+ return 0;
+}
+
+static int apply_r_riscv_set16_rela(struct module *me, u32 *location,
+ Elf_Addr v)
+{
+ *(u16 *)location = (u16)v;
+ return 0;
+}
+
+static int apply_r_riscv_set32_rela(struct module *me, u32 *location,
+ Elf_Addr v)
+{
+ *(u32 *)location = (u32)v;
+ return 0;
+}
+
+static int apply_r_riscv_32_pcrel_rela(struct module *me, u32 *location,
+ Elf_Addr v)
+{
+ *(u32 *)location = (u32)v;
+ return 0;
+}
+
+static int apply_r_riscv_plt32_rela(struct module *me, u32 *location,
+ Elf_Addr v)
+{
+ *(u32 *)location = (u32)v;
+ return 0;
+}
+
+static int apply_r_riscv_set_uleb128(struct module *me, u32 *location, Elf_Addr v)
+{
+ /*
+ * Relocation is only performed if R_RISCV_SET_ULEB128 is followed by
+ * R_RISCV_SUB_ULEB128 so do computation there
+ */
+ return 0;
+}
+
+static int apply_r_riscv_sub_uleb128(struct module *me, u32 *location, Elf_Addr v)
+{
+ if (v >= 128) {
+ pr_err("%s: uleb128 must be in [0, 127] (not %ld) at PC = %p\n",
+ me->name, (unsigned long)v, location);
+ return -EINVAL;
+ }
+
+ *location = v;
+ return 0;
+}
+
+/*
+ * Relocations defined in the riscv-elf-psabi-doc.
+ * This handles static linking only.
+ */
+static int (*reloc_handlers_rela[])(struct module *me, u32 *location,
+ Elf_Addr v) = {
+ [R_RISCV_32] = apply_r_riscv_32_rela,
+ [R_RISCV_64] = apply_r_riscv_64_rela,
+ [R_RISCV_RELATIVE] = dynamic_linking_not_supported,
+ [R_RISCV_COPY] = dynamic_linking_not_supported,
+ [R_RISCV_JUMP_SLOT] = dynamic_linking_not_supported,
+ [R_RISCV_TLS_DTPMOD32] = dynamic_linking_not_supported,
+ [R_RISCV_TLS_DTPMOD64] = dynamic_linking_not_supported,
+ [R_RISCV_TLS_DTPREL32] = dynamic_linking_not_supported,
+ [R_RISCV_TLS_DTPREL64] = dynamic_linking_not_supported,
+ [R_RISCV_TLS_TPREL32] = dynamic_linking_not_supported,
+ [R_RISCV_TLS_TPREL64] = dynamic_linking_not_supported,
+ /* 12-15 undefined */
+ [R_RISCV_BRANCH] = apply_r_riscv_branch_rela,
+ [R_RISCV_JAL] = apply_r_riscv_jal_rela,
+ [R_RISCV_CALL] = apply_r_riscv_call_rela,
+ [R_RISCV_CALL_PLT] = apply_r_riscv_call_plt_rela,
+ [R_RISCV_GOT_HI20] = apply_r_riscv_got_hi20_rela,
+ [R_RISCV_TLS_GOT_HI20] = tls_not_supported,
+ [R_RISCV_TLS_GD_HI20] = tls_not_supported,
+ [R_RISCV_PCREL_HI20] = apply_r_riscv_pcrel_hi20_rela,
+ [R_RISCV_PCREL_LO12_I] = apply_r_riscv_pcrel_lo12_i_rela,
+ [R_RISCV_PCREL_LO12_S] = apply_r_riscv_pcrel_lo12_s_rela,
+ [R_RISCV_HI20] = apply_r_riscv_hi20_rela,
+ [R_RISCV_LO12_I] = apply_r_riscv_lo12_i_rela,
+ [R_RISCV_LO12_S] = apply_r_riscv_lo12_s_rela,
+ [R_RISCV_TPREL_HI20] = tls_not_supported,
+ [R_RISCV_TPREL_LO12_I] = tls_not_supported,
+ [R_RISCV_TPREL_LO12_S] = tls_not_supported,
+ [R_RISCV_TPREL_ADD] = tls_not_supported,
+ [R_RISCV_ADD8] = apply_r_riscv_add8_rela,
+ [R_RISCV_ADD16] = apply_r_riscv_add16_rela,
+ [R_RISCV_ADD32] = apply_r_riscv_add32_rela,
+ [R_RISCV_ADD64] = apply_r_riscv_add64_rela,
+ [R_RISCV_SUB8] = apply_r_riscv_sub8_rela,
+ [R_RISCV_SUB16] = apply_r_riscv_sub16_rela,
+ [R_RISCV_SUB32] = apply_r_riscv_sub32_rela,
+ [R_RISCV_SUB64] = apply_r_riscv_sub64_rela,
+ /* 41-42 reserved for future standard use */
+ [R_RISCV_ALIGN] = apply_r_riscv_align_rela,
+ [R_RISCV_RVC_BRANCH] = apply_r_riscv_rvc_branch_rela,
+ [R_RISCV_RVC_JUMP] = apply_r_riscv_rvc_jump_rela,
+ [R_RISCV_RVC_LUI] = apply_r_riscv_rvc_lui_rela,
+ /* 47-50 reserved for future standard use */
+ [R_RISCV_RELAX] = apply_r_riscv_relax_rela,
+ [R_RISCV_SUB6] = apply_r_riscv_sub6_rela,
+ [R_RISCV_SET6] = apply_r_riscv_set6_rela,
+ [R_RISCV_SET8] = apply_r_riscv_set8_rela,
+ [R_RISCV_SET16] = apply_r_riscv_set16_rela,
+ [R_RISCV_SET32] = apply_r_riscv_set32_rela,
+ [R_RISCV_32_PCREL] = apply_r_riscv_32_pcrel_rela,
+ [R_RISCV_IRELATIVE] = dynamic_linking_not_supported,
+ [R_RISCV_PLT32] = apply_r_riscv_plt32_rela,
+ [R_RISCV_SET_ULEB128] = apply_r_riscv_set_uleb128,
+ [R_RISCV_SUB_ULEB128] = apply_r_riscv_sub_uleb128,
+ /* 62-191 reserved for future standard use */
+ /* 192-255 nonstandard ABI extensions */
};

int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
@@ -425,6 +581,47 @@ int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
me->name);
return -EINVAL;
}
+ } else if (type == R_RISCV_SUB_ULEB128) {
+ unsigned long set_loc;
+ u32 set_type;
+ unsigned long set_sym_val;
+
+ bool has_corresponding_relocation = false;
+
+ /* R_RISCV_SET_ULEB128 must appear before the SUB */
+ for (unsigned int j = i; j >= 0; j--) {
+ set_loc = sechdrs[sechdrs[relsec].sh_info]
+ .sh_addr +
+ rel[j].r_offset;
+ set_type = ELF_RISCV_R_TYPE(rel[j].r_info);
+
+ /*
+ * Find the SET relocation that is targeting the
+ * same position as the SUB
+ */
+ if (set_type == R_RISCV_SET_ULEB128 &&
+ set_loc == (unsigned long)location) {
+ Elf_Sym *corresponding_sym =
+ (Elf_Sym *)sechdrs[symindex]
+ .sh_addr +
+ ELF_RISCV_R_SYM(rel[j].r_info);
+
+ set_sym_val =
+ corresponding_sym->st_value +
+ rel[j].r_addend;
+ has_corresponding_relocation = true;
+ break;
+ }
+ }
+
+ if (has_corresponding_relocation) {
+ /* Calculate set and subtraction */
+ v = set_sym_val - v;
+ } else {
+ pr_err("%s: R_RISCV_SUB_ULEB128 must always be paired with a R_RISCV_SET_ULEB128 that comes before it. PC = %p\n",
+ me->name, location);
+ return -EINVAL;
+ }
}

res = handler(me, location, v);

--
2.34.1

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