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

Andrew Jones
2023-01-20T18:34:25Z

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.

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