Re: [PATCH v4 1/2] riscv: Add remaining module relocations

From: Charlie Jenkins
Date: Wed Oct 18 2023 - 18:19:21 EST

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On Wed, Oct 18, 2023 at 01:28:45PM -0500, Samuel Holland wrote:
> On 2023-10-18 12:34 AM, Charlie Jenkins wrote:
> > 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 | 5 +-
> > arch/riscv/kernel/module.c | 207 +++++++++++++++++++++++++++++++++-----
> > 2 files changed, 186 insertions(+), 26 deletions(-)
> >
> > diff --git a/arch/riscv/include/uapi/asm/elf.h b/arch/riscv/include/uapi/asm/elf.h
> > index d696d6610231..11a71b8533d5 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 +82,6 @@ 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_GPREL_I 47
> > #define R_RISCV_GPREL_S 48
> > #define R_RISCV_TPREL_I 49
> > @@ -93,6 +93,9 @@ 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..e860726352ac 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>
> > @@ -268,6 +269,12 @@ 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 +296,12 @@ 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 +323,149 @@ 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 = (*location - ((u8)v & 0x3F)) & 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;
>
> You don't need to cast the pointer, since it's already a `u32 *`.
>
> > + return 0;
> > +}
> > +
> > +static int apply_r_riscv_32_pcrel_rela(struct module *me, u32 *location,
> > + Elf_Addr v)
> > +{
> > + *(u32 *)location = (u32)v;
>
> This expression should be:
>
> *location = v - location;
>
> matching the other PC-relative relocations.
>
> (BTW, recent clang generates these relocations for module alternatives.)
>
> > + return 0;
> > +}
> > +
> > +static int apply_r_riscv_plt32_rela(struct module *me, u32 *location,
> > + Elf_Addr v)
> > +{
> > + *(u32 *)location = (u32)v;
>
> This should look like apply_r_riscv_32_pcrel_rela(), but with the PLT entry
> emission code from apply_r_riscv_call_plt_rela(). See the psABI commit[1].
>
> [1]:
> https://github.com/riscv-non-isa/riscv-elf-psabi-doc/commit/c3f8269c56d8a2f56c2602f2a44175362024ef9c
>

Thank you for pointing out these issues.

> > + 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,
> > + /* 46-50 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,
> > @@ -348,6 +479,10 @@ int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
> > unsigned int i, type;
> > Elf_Addr v;
> > int res;
> > + bool uleb128_set_exists = false;
> > + u32 *uleb128_set_loc;
> > + unsigned long uleb128_set_sym_val;
> > +
>
> Extra blank line.
>
> >
> > pr_debug("Applying relocate section %u to %u\n", relsec,
> > sechdrs[relsec].sh_info);
> > @@ -425,6 +560,28 @@ int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
> > me->name);
> > return -EINVAL;
> > }
> > + } else if (type == R_RISCV_SET_ULEB128) {
> > + if (uleb128_set_exists) {
> > + pr_err("%s: riscv psABI requires the next ULEB128 relocation to come after a R_RISCV_SET_ULEB128 is an R_RISCV_SUB_ULEB128, not another R_RISCV_SET_ULEB128.\n",
> > + me->name);
> > + return -EINVAL;
> > + }
> > + uleb128_set_exists = true;
> > + uleb128_set_loc = location;
> > + uleb128_set_sym_val =
> > + ((Elf_Sym *)sechdrs[symindex].sh_addr +
> > + ELF_RISCV_R_SYM(rel[i].r_info))
> > + ->st_value +
> > + rel[i].r_addend;
> > + } else if (type == R_RISCV_SUB_ULEB128) {
> > + if (uleb128_set_exists && uleb128_set_loc == location) {
> > + /* Calculate set and subtraction */
> > + v = uleb128_set_sym_val - v;
>
> You need to set uleb128_set_exists back to false somewhere, or you can only
> handle one R_RISCV_SET_ULEB128 relocation per module.
>

I guess that never made it out of my thoughts and into the code...

- Charlie

> Regards,
> Samuel
>
> > + } else {
> > + pr_err("%s: R_RISCV_SUB_ULEB128 must always be paired with the first R_RISCV_SET_ULEB128 that comes before it. PC = %p\n",
> > + me->name, location);
> > + return -EINVAL;
> > + }
> > }
> >
> > res = handler(me, location, v);
> >
>

Next message: Charlie Jenkins: "Re: [PATCH v4 1/2] riscv: Add remaining module relocations"
Previous message: Dongli Zhang: "[PATCH RFC 1/1] x86/paravirt: introduce param to disable pv sched_clock"
In reply to: Samuel Holland: "Re: [PATCH v4 1/2] riscv: Add remaining module relocations"
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