Subject: [PATCH v6 4/6] arm64: insn: add instruction decoders for ldp/stp and add/sub

From: [email-masked] (Will Deacon)
Date: Tue, 8 Dec 2015 18:15:17 +0000

On Wed, Nov 18, 2015 at 03:43:07PM +0900, AKASHI Takahiro wrote:
> A function prologue analyzer is a requisite for implementing stack tracer
> and getting better views of stack usages on arm64.
> To implement a function prologue analyzer, we have to be able to decode,
> at least, stp, add, sub and mov instructions.
> 
> This patch adds decoders for those instructions, that are used solely
> by stack tracer for now, but generic enough for other uses.
> 
> Reviewed-by: Jungseok Lee <[email-masked]>
> Tested-by: Jungseok Lee <[email-masked]>
> Signed-off-by: AKASHI Takahiro <[email-masked]>
> ---
>  arch/arm64/include/asm/insn.h |   18 ++++++++
>  arch/arm64/kernel/insn.c      |  102 +++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 120 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/insn.h b/arch/arm64/include/asm/insn.h
> index 30e50eb..8d5c538 100644
> --- a/arch/arm64/include/asm/insn.h
> +++ b/arch/arm64/include/asm/insn.h
> @@ -165,6 +165,8 @@ enum aarch64_insn_ldst_type {
>  	AARCH64_INSN_LDST_STORE_PAIR_PRE_INDEX,
>  	AARCH64_INSN_LDST_LOAD_PAIR_POST_INDEX,
>  	AARCH64_INSN_LDST_STORE_PAIR_POST_INDEX,
> +	AARCH64_INSN_LDST_LOAD_PAIR,
> +	AARCH64_INSN_LDST_STORE_PAIR,

For consistency with the rest of this header, we should be calling these
AARCH64_INSN_LDST_{LOAD,STORE}_PAIR_REG_OFFSET...

>  };
>  
>  enum aarch64_insn_adsb_type {
> @@ -225,6 +227,8 @@ static __always_inline u32 aarch64_insn_get_##abbr##_value(void) \
>  
>  __AARCH64_INSN_FUNCS(str_reg,	0x3FE0EC00, 0x38206800)
>  __AARCH64_INSN_FUNCS(ldr_reg,	0x3FE0EC00, 0x38606800)
> +__AARCH64_INSN_FUNCS(stp,	0x7FC00000, 0x29000000)
> +__AARCH64_INSN_FUNCS(ldp,	0x7FC00000, 0x29400000)

... and using stp_reg/ldp_reg here.

>  __AARCH64_INSN_FUNCS(stp_post,	0x7FC00000, 0x28800000)
>  __AARCH64_INSN_FUNCS(ldp_post,	0x7FC00000, 0x28C00000)
>  __AARCH64_INSN_FUNCS(stp_pre,	0x7FC00000, 0x29800000)
> @@ -277,6 +281,7 @@ __AARCH64_INSN_FUNCS(hint,	0xFFFFF01F, 0xD503201F)
>  __AARCH64_INSN_FUNCS(br,	0xFFFFFC1F, 0xD61F0000)
>  __AARCH64_INSN_FUNCS(blr,	0xFFFFFC1F, 0xD63F0000)
>  __AARCH64_INSN_FUNCS(ret,	0xFFFFFC1F, 0xD65F0000)
> +__AARCH64_INSN_FUNCS(eret,	0xFFFFFFFF, 0xD69F00E0)

Is this encoding correct? I ended up with 0xd69f03e0.

>  #undef	__AARCH64_INSN_FUNCS
>  
> @@ -370,6 +375,19 @@ bool aarch32_insn_is_wide(u32 insn);
>  u32 aarch32_insn_extract_reg_num(u32 insn, int offset);
>  u32 aarch32_insn_mcr_extract_opc2(u32 insn);
>  u32 aarch32_insn_mcr_extract_crm(u32 insn);
> +int aarch64_insn_decode_add_sub_imm(u32 insn,
> +				    enum aarch64_insn_register *dst,
> +				    enum aarch64_insn_register *src,
> +				    int *imm,
> +				    enum aarch64_insn_variant *variant,
> +				    enum aarch64_insn_adsb_type *type);
> +int aarch64_insn_decode_load_store_pair(u32 insn,
> +					enum aarch64_insn_register *reg1,
> +					enum aarch64_insn_register *reg2,
> +					enum aarch64_insn_register *base,
> +					int *offset,
> +					enum aarch64_insn_variant *variant,
> +					enum aarch64_insn_ldst_type *type);
>  #endif /* __ASSEMBLY__ */
>  
>  #endif	/* __ASM_INSN_H */
> diff --git a/arch/arm64/kernel/insn.c b/arch/arm64/kernel/insn.c
> index c08b9ad..b56a66c 100644
> --- a/arch/arm64/kernel/insn.c
> +++ b/arch/arm64/kernel/insn.c
> @@ -33,6 +33,7 @@
>  #include <asm/insn.h>
>  
>  #define AARCH64_INSN_SF_BIT	BIT(31)
> +#define AARCH64_INSN_S_BIT	BIT(29)
>  #define AARCH64_INSN_N_BIT	BIT(22)
>  
>  static int aarch64_insn_encoding_class[] = {
> @@ -1141,3 +1142,104 @@ u32 aarch32_insn_mcr_extract_crm(u32 insn)
>  {
>  	return insn & CRM_MASK;
>  }
> +
> +enum aarch64_insn_register aarch64_insn_extract_reg_num(u32 insn,
> +				enum aarch64_insn_register_type type)

Maybe call this aarch64_insn_decode_register? You're basically building
decoders for some of the *_encode_* functions we already have.

> +{
> +	int shift;
> +
> +	switch (type) {
> +	case AARCH64_INSN_REGTYPE_RT:
> +	case AARCH64_INSN_REGTYPE_RD:
> +		shift = 0;
> +		break;
> +	case AARCH64_INSN_REGTYPE_RN:
> +		shift = 5;
> +		break;
> +	case AARCH64_INSN_REGTYPE_RT2:
> +	case AARCH64_INSN_REGTYPE_RA:
> +		shift = 10;
> +		break;
> +	case AARCH64_INSN_REGTYPE_RM:
> +		shift = 16;
> +		break;
> +	default:
> +		pr_err("%s: unknown register type decoding %d\n", __func__,
> +		       type);
> +		return ~0L;
> +	}

This is largely a copy-paste from aarch64_insn_encode_register. Can you
either work with what we have or factor out the common parts, please?

> +	return (insn & (GENMASK(4, 0) << shift)) >> shift;
> +}
> +
> +int aarch64_insn_decode_add_sub_imm(u32 insn,

This one could be aarch64_insn_extract_add_sub_imm, if you like.
Then extract is the converse of gen and decode is the converse of encode.

> +				    enum aarch64_insn_register *dst,
> +				    enum aarch64_insn_register *src,
> +				    int *imm,
> +				    enum aarch64_insn_variant *variant,
> +				    enum aarch64_insn_adsb_type *type)
> +{
> +	if (aarch64_insn_is_add_imm(insn))
> +		*type =	((insn) & AARCH64_INSN_S_BIT) ?
> +				AARCH64_INSN_ADSB_ADD_SETFLAGS :
> +				AARCH64_INSN_ADSB_ADD;
> +	else if (aarch64_insn_is_sub_imm(insn))
> +		*type =	((insn) & AARCH64_INSN_S_BIT) ?
> +				AARCH64_INSN_ADSB_SUB_SETFLAGS :
> +				AARCH64_INSN_ADSB_SUB;
> +	else
> +		return 0;

Why do we need to return 0 on error? -EINVAL might make more sense.

> +
> +	*variant = (insn & AARCH64_INSN_SF_BIT) ? AARCH64_INSN_VARIANT_64BIT :
> +					AARCH64_INSN_VARIANT_32BIT;
> +
> +	*dst = aarch64_insn_extract_reg_num(insn, AARCH64_INSN_REGTYPE_RD);
> +
> +	*src = aarch64_insn_extract_reg_num(insn, AARCH64_INSN_REGTYPE_RN);
> +
> +	/* TODO: ignore shilft field[23:22] */

I don't understand the TODO.

> +	*imm = (int)aarch64_insn_decode_immediate(AARCH64_INSN_IMM_12, insn);

We use u64 for imm everywhere else.

> +	return 1;
> +}

Similarly here, you're trying to implement the converse of
aarch64_insn_gen_add_sub_imm

> +
> +int aarch64_insn_decode_load_store_pair(u32 insn,
> +					enum aarch64_insn_register *reg1,
> +					enum aarch64_insn_register *reg2,
> +					enum aarch64_insn_register *base,
> +					int *offset,
> +					enum aarch64_insn_variant *variant,
> +					enum aarch64_insn_ldst_type *type)
> +{
> +	int imm;
> +
> +	if (aarch64_insn_is_stp(insn))
> +		*type = AARCH64_INSN_LDST_STORE_PAIR;
> +	else if (aarch64_insn_is_stp_post(insn))
> +		*type = AARCH64_INSN_LDST_STORE_PAIR_POST_INDEX;
> +	else if (aarch64_insn_is_stp_pre(insn))
> +		*type = AARCH64_INSN_LDST_STORE_PAIR_PRE_INDEX;
> +	else if (aarch64_insn_is_ldp(insn))
> +		*type = AARCH64_INSN_LDST_LOAD_PAIR;
> +	else if (aarch64_insn_is_ldp_post(insn))
> +		*type = AARCH64_INSN_LDST_LOAD_PAIR_POST_INDEX;
> +	else if (aarch64_insn_is_ldp_pre(insn))
> +		*type = AARCH64_INSN_LDST_LOAD_PAIR_PRE_INDEX;
> +	else
> +		return 0;
> +
> +	*variant = (insn & AARCH64_INSN_S_BIT) ? AARCH64_INSN_VARIANT_64BIT :
> +				AARCH64_INSN_VARIANT_32BIT;
> +
> +	*reg1 = aarch64_insn_extract_reg_num(insn, AARCH64_INSN_REGTYPE_RT);
> +
> +	*reg2 = aarch64_insn_extract_reg_num(insn, AARCH64_INSN_REGTYPE_RT2);
> +
> +	*base = aarch64_insn_extract_reg_num(insn, AARCH64_INSN_REGTYPE_RN);
> +
> +	imm = (int)aarch64_insn_decode_immediate(AARCH64_INSN_IMM_7, insn);
> +	asm("sbfm %0, %0, 0, 6" : "+r" (imm));

What? Can't you write this in C?

Will