Re: [PATCH v4 09/13] riscv: switch to relative alternative entries

Andrew Jones
2023-01-26T07:09:37Z

On Fri, Jan 20, 2023 at 07:34:18PM +0100, Andrew Jones wrote:
> On Sun, Jan 15, 2023 at 11:49:49PM +0800, Jisheng Zhang wrote:
> ...
> > #define ALT_ENTRY(oldptr, newptr, vendor_id, errata_id, newlen) \
> > - RISCV_PTR " " oldptr "\n" \
> > - RISCV_PTR " " newptr "\n" \
> > - REG_ASM " " vendor_id "\n" \
> > - REG_ASM " " newlen "\n" \
> > - ".word " errata_id "\n"
> > + ".4byte ((" oldptr ") - .) \n" \
> > + ".4byte ((" newptr ") - .) \n" \
> > + ".2byte " vendor_id "\n" \
> > + ".2byte " newlen "\n" \
> > + ".4byte " errata_id "\n"
> >
>
> Hi Jisheng,
>
> This patch breaks loading the KVM module for me. I got "kvm: Unknown
> relocation type 34". My guess is that these 2 byte fields are inspiring
> the compiler to emit 16-bit relocation types. The patch below fixes
> things for me. If you agree with fixing it this way, rather than
> changing something in alternatives, like not using 2 byte fields,
> then please pick the below patch up in your series.

Hi Jisheng,

I'm poking again on this as I see this series is now working its way
to be merged into for-next. I'd rather avoid the bisection breakage
which will be present if we fix this issue afterwards by having a
v5 merged which addresses the issue in the correct patch order.

Thanks,
drew

>
> From 4d203697aa745a0cd3a9217d547a9fb7fa2a87c7 Mon Sep 17 00:00:00 2001
> From: Andrew Jones <ajones@ventanamicro.com>
> Date: Fri, 20 Jan 2023 19:05:44 +0100
> Subject: [PATCH] riscv: module: Add ADD16 and SUB16 rela types
> Content-type: text/plain
>
> To prepare for 16-bit relocation types to be emitted in alternatives
> add support for ADD16 and SUB16.
>
> Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
> ---
> arch/riscv/kernel/module.c | 16 ++++++++++++++++
> 1 file changed, 16 insertions(+)
>
> diff --git a/arch/riscv/kernel/module.c b/arch/riscv/kernel/module.c
> index 76f4b9c2ec5b..7c651d55fcbd 100644
> --- a/arch/riscv/kernel/module.c
> +++ b/arch/riscv/kernel/module.c
> @@ -268,6 +268,13 @@ static int apply_r_riscv_align_rela(struct module *me, u32 *location,
> return -EINVAL;
> }
>
> +static int apply_r_riscv_add16_rela(struct module *me, u32 *location,
> + Elf_Addr v)
> +{
> + *(u16 *)location += (u16)v;
> + return 0;
> +}
> +
> static int apply_r_riscv_add32_rela(struct module *me, u32 *location,
> Elf_Addr v)
> {
> @@ -282,6 +289,13 @@ static int apply_r_riscv_add64_rela(struct module *me, u32 *location,
> return 0;
> }
>
> +static int apply_r_riscv_sub16_rela(struct module *me, u32 *location,
> + Elf_Addr v)
> +{
> + *(u16 *)location -= (u16)v;
> + return 0;
> +}
> +
> static int apply_r_riscv_sub32_rela(struct module *me, u32 *location,
> Elf_Addr v)
> {
> @@ -315,8 +329,10 @@ static int (*reloc_handlers_rela[]) (struct module *me, u32 *location,
> [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,
> };
> --
> 2.39.0
>