Subject: Re: [PATCH 09/12] riscv: extable: add `type` and `data` fields

From: Jisheng Zhang <[email-masked]>
Date: Thu, 18 Nov 2021 19:42:49 +0800

On Thu, 18 Nov 2021 19:26:05 +0800 Jisheng Zhang wrote:

> From: Jisheng Zhang <[email-masked]>
> 
> This is a riscv port of commit d6e2cc564775("arm64: extable: add `type`
> and `data` fields").
> 
> We will add specialized handlers for fixups, the `type` field is for
> fixup handler type, the `data` field is used to pass specific data to
> each handler, for example register numbers.
> 
> Signed-off-by: Jisheng Zhang <[email-masked]>
> ---
>  arch/riscv/include/asm/asm-extable.h | 25 +++++++++++++++++--------
>  arch/riscv/include/asm/extable.h     | 17 ++++++++++++++---
>  arch/riscv/kernel/vmlinux.lds.S      |  2 +-
>  arch/riscv/mm/extable.c              | 25 +++++++++++++++++++++----
>  arch/riscv/net/bpf_jit_comp64.c      |  5 +++--
>  scripts/sorttable.c                  |  4 +++-
>  6 files changed, 59 insertions(+), 19 deletions(-)
> 
> diff --git a/arch/riscv/include/asm/asm-extable.h b/arch/riscv/include/asm/asm-extable.h
> index b790c02dbdda..1b1f4ffd8d37 100644
> --- a/arch/riscv/include/asm/asm-extable.h
> +++ b/arch/riscv/include/asm/asm-extable.h
> @@ -2,31 +2,40 @@
>  #ifndef __ASM_ASM_EXTABLE_H
>  #define __ASM_ASM_EXTABLE_H
>  
> +#define EX_TYPE_NONE			0
> +#define EX_TYPE_FIXUP			1
> +#define EX_TYPE_BPF			2
> +
>  #ifdef __ASSEMBLY__
>  
> -#define __ASM_EXTABLE_RAW(insn, fixup)		\
> -	.pushsection	__ex_table, "a";	\
> -	.balign		4;			\
> -	.long		((insn) - .);		\
> -	.long		((fixup) - .);		\
> +#define __ASM_EXTABLE_RAW(insn, fixup, type, data)	\
> +	.pushsection	__ex_table, "a";		\
> +	.balign		4;				\
> +	.long		((insn) - .);			\
> +	.long		((fixup) - .);			\
> +	.short		(type);				\
> +	.short		(data);				\
>  	.popsection;
>  
>  	.macro		_asm_extable, insn, fixup
> -	__ASM_EXTABLE_RAW(\insn, \fixup)
> +	__ASM_EXTABLE_RAW(\insn, \fixup, EX_TYPE_FIXUP, 0)
>  	.endm
>  
>  #else /* __ASSEMBLY__ */
>  
>  #include <linux/stringify.h>
>  
> -#define __ASM_EXTABLE_RAW(insn, fixup)			\
> +#define __ASM_EXTABLE_RAW(insn, fixup, type, data)	\
>  	".pushsection	__ex_table, \"a\"\n"		\
>  	".balign	4\n"				\
>  	".long		((" insn ") - .)\n"		\
>  	".long		((" fixup ") - .)\n"		\
> +	".short		(" type ")\n"			\
> +	".short		(" data ")\n"			\
>  	".popsection\n"
>  
> -#define _ASM_EXTABLE(insn, fixup) __ASM_EXTABLE_RAW(#insn, #fixup)
> +#define _ASM_EXTABLE(insn, fixup)	\
> +	__ASM_EXTABLE_RAW(#insn, #fixup, __stringify(EX_TYPE_FIXUP), "0")
>  
>  #endif /* __ASSEMBLY__ */
>  
> diff --git a/arch/riscv/include/asm/extable.h b/arch/riscv/include/asm/extable.h
> index e4374dde02b4..512012d193dc 100644
> --- a/arch/riscv/include/asm/extable.h
> +++ b/arch/riscv/include/asm/extable.h
> @@ -17,18 +17,29 @@
>  
>  struct exception_table_entry {
>  	int insn, fixup;
> +	short type, data;
>  };
>  
>  #define ARCH_HAS_RELATIVE_EXTABLE
>  
> +#define swap_ex_entry_fixup(a, b, tmp, delta)		\
> +do {							\
> +	(a)->fixup = (b)->fixup + (delta);		\
> +	(b)->fixup = (tmp).fixup - (delta);		\
> +	(a)->type = (b)->type;				\
> +	(b)->type = (tmp).type;				\
> +	(a)->data = (b)->data;				\
> +	(b)->data = (tmp).data;				\
> +} while (0)
> +
>  bool fixup_exception(struct pt_regs *regs);
>  
>  #if defined(CONFIG_BPF_JIT) && defined(CONFIG_ARCH_RV64I)
> -bool rv_bpf_fixup_exception(const struct exception_table_entry *ex, struct pt_regs *regs);
> +bool ex_handler_bpf(const struct exception_table_entry *ex, struct pt_regs *regs);
>  #else
>  static inline bool
> -rv_bpf_fixup_exception(const struct exception_table_entry *ex,
> -		       struct pt_regs *regs)
> +ex_handler_bpf(const struct exception_table_entry *ex,
> +	       struct pt_regs *regs)
>  {
>  	return false;
>  }
> diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
> index 5104f3a871e3..0e5ae851929e 100644
> --- a/arch/riscv/kernel/vmlinux.lds.S
> +++ b/arch/riscv/kernel/vmlinux.lds.S
> @@ -4,7 +4,7 @@
>   * Copyright (C) 2017 SiFive
>   */
>  
> -#define RO_EXCEPTION_TABLE_ALIGN	16
> +#define RO_EXCEPTION_TABLE_ALIGN	4
>  
>  #ifdef CONFIG_XIP_KERNEL
>  #include "vmlinux-xip.lds.S"
> diff --git a/arch/riscv/mm/extable.c b/arch/riscv/mm/extable.c
> index 3c561f1d0115..91e52c4bb33a 100644
> --- a/arch/riscv/mm/extable.c
> +++ b/arch/riscv/mm/extable.c
> @@ -10,6 +10,20 @@
>  #include <linux/extable.h>
>  #include <linux/module.h>
>  #include <linux/uaccess.h>
> +#include <asm/asm-extable.h>
> +
> +static inline unsigned long
> +get_ex_fixup(const struct exception_table_entry *ex)
> +{
> +	return ((unsigned long)&ex->fixup + ex->fixup);
> +}
> +
> +static bool ex_handler_fixup(const struct exception_table_entry *ex,
> +			     struct pt_regs *regs)
> +{
> +	regs->epc = get_ex_fixup(ex);
> +	return true;
> +}
>  
>  bool fixup_exception(struct pt_regs *regs)
>  {
> @@ -19,9 +33,12 @@ bool fixup_exception(struct pt_regs *regs)
>  	if (!ex)
>  		return false;
>  
> -	if (regs->epc >= BPF_JIT_REGION_START && regs->epc < BPF_JIT_REGION_END)
> -		return rv_bpf_fixup_exception(ex, regs);
> +	switch (ex->type) {
> +	case EX_TYPE_FIXUP:
> +		return ex_handler_fixup(ex, regs);
> +	case EX_TYPE_BPF:
> +		return ex_handler_bpf(ex, regs);
> +	}
>  
> -	regs->epc = (unsigned long)&ex->fixup + ex->fixup;
> -	return true;
> +	BUG();
>  }
> diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
> index 7714081cbb64..69bab7e28f91 100644
> --- a/arch/riscv/net/bpf_jit_comp64.c
> +++ b/arch/riscv/net/bpf_jit_comp64.c
> @@ -459,8 +459,8 @@ static int emit_call(bool fixed, u64 addr, struct rv_jit_context *ctx)
>  #define BPF_FIXUP_OFFSET_MASK   GENMASK(26, 0)
>  #define BPF_FIXUP_REG_MASK      GENMASK(31, 27)
>  
> -bool rv_bpf_fixup_exception(const struct exception_table_entry *ex,
> -			    struct pt_regs *regs)
> +bool ex_handler_bpf(const struct exception_table_entry *ex,
> +		    struct pt_regs *regs)
>  {
>  	off_t offset = FIELD_GET(BPF_FIXUP_OFFSET_MASK, ex->fixup);
>  	int regs_offset = FIELD_GET(BPF_FIXUP_REG_MASK, ex->fixup);
> @@ -514,6 +514,7 @@ static int add_exception_handler(const struct bpf_insn *insn,
>  
>  	ex->fixup = FIELD_PREP(BPF_FIXUP_OFFSET_MASK, offset) |
>  		FIELD_PREP(BPF_FIXUP_REG_MASK, dst_reg);
> +	ex->type = EX_TYPE_BPF;
>  
>  	ctx->nexentries++;
>  	return 0;
> diff --git a/scripts/sorttable.c b/scripts/sorttable.c
> index 0c031e47a419..5b5472b543f5 100644
> --- a/scripts/sorttable.c
> +++ b/scripts/sorttable.c
> @@ -376,9 +376,11 @@ static int do_file(char const *const fname, void *addr)
>  	case EM_PARISC:
>  	case EM_PPC:
>  	case EM_PPC64:
> -	case EM_RISCV:
>  		custom_sort = sort_relative_table;
>  		break;
> +	case EM_RISCV:
> +		custom_sort = arm64_sort_relative_table;

Hi Mark, Thomas,

x86 and arm64 version of sort_relative_table routine are the same, I want to
unify them, and then use the common function for riscv, but I'm not sure
which name is better. Could you please suggest?

Thanks	

> +		break;
>  	case EM_ARCOMPACT:
>  	case EM_ARCV2:
>  	case EM_ARM: