Re: [PATCH 05/10] x86/insn: Add support for REX2 prefix to the instruction decoder logic

From: Ian Rogers
Date: Thu May 02 2024 - 14:10:47 EST

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In reply to: tip-bot2 for Adrian Hunter: "[tip: perf/core] x86/insn: Add support for REX2 prefix to the instruction decoder logic"
Next in thread: Adrian Hunter: "Re: [PATCH 05/10] x86/insn: Add support for REX2 prefix to the instruction decoder logic"
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On Thu, May 2, 2024 at 3:59 AM Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote:
>
> Intel Advanced Performance Extensions (APX) uses a new 2-byte prefix named
> REX2 to select extended general purpose registers (EGPRs) i.e. r16 to r31.
>
> The REX2 prefix is effectively an extended version of the REX prefix.
>
> REX2 and EVEX are also used with PUSH/POP instructions to provide a
> Push-Pop Acceleration (PPX) hint. With PPX hints, a CPU will attempt to
> fast-forward register data between matching PUSH and POP instructions.
>
> REX2 is valid only with opcodes in maps 0 and 1. Similar extension for
> other maps is provided by the EVEX prefix, covered in a separate patch.
>
> Some opcodes in maps 0 and 1 are reserved under REX2. One of these is used
> for a new 64-bit absolute direct jump instruction JMPABS.
>
> Refer to the Intel Advanced Performance Extensions (Intel APX) Architecture
> Specification for details.
>
> Define a code value for the REX2 prefix (INAT_PFX_REX2), and add attribute
> flags for opcodes reserved under REX2 (INAT_NO_REX2) and to identify
> opcodes (only JMPABS) that require a mandatory REX2 prefix
> (INAT_REX2_VARIANT).
>
> Amend logic to read the REX2 prefix and get the opcode attribute for the
> map number (0 or 1) encoded in the REX2 prefix.
>
> Amend the awk script that generates the attribute tables from the opcode
> map, to recognise "REX2" as attribute INAT_PFX_REX2, and "(!REX2)"
> as attribute INAT_NO_REX2, and "(REX2)" as attribute INAT_REX2_VARIANT.
>
> Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
> ---
> arch/x86/include/asm/inat.h | 11 +++++++++-
> arch/x86/include/asm/insn.h | 25 ++++++++++++++++++----
> arch/x86/lib/insn.c | 25 ++++++++++++++++++++++
> arch/x86/tools/gen-insn-attr-x86.awk | 11 +++++++++-
> tools/arch/x86/include/asm/inat.h | 11 +++++++++-
> tools/arch/x86/include/asm/insn.h | 25 ++++++++++++++++++----
> tools/arch/x86/lib/insn.c | 25 ++++++++++++++++++++++
> tools/arch/x86/tools/gen-insn-attr-x86.awk | 11 +++++++++-
> 8 files changed, 132 insertions(+), 12 deletions(-)
>
> diff --git a/arch/x86/include/asm/inat.h b/arch/x86/include/asm/inat.h
> index b56c5741581a..1331bdd39a23 100644
> --- a/arch/x86/include/asm/inat.h
> +++ b/arch/x86/include/asm/inat.h
> @@ -35,6 +35,8 @@
> #define INAT_PFX_VEX2 13 /* 2-bytes VEX prefix */
> #define INAT_PFX_VEX3 14 /* 3-bytes VEX prefix */
> #define INAT_PFX_EVEX 15 /* EVEX prefix */
> +/* x86-64 REX2 prefix */
> +#define INAT_PFX_REX2 16 /* 0xD5 */
>
> #define INAT_LSTPFX_MAX 3
> #define INAT_LGCPFX_MAX 11
> @@ -50,7 +52,7 @@
>
> /* Legacy prefix */
> #define INAT_PFX_OFFS 0
> -#define INAT_PFX_BITS 4
> +#define INAT_PFX_BITS 5
> #define INAT_PFX_MAX ((1 << INAT_PFX_BITS) - 1)
> #define INAT_PFX_MASK (INAT_PFX_MAX << INAT_PFX_OFFS)
> /* Escape opcodes */
> @@ -77,6 +79,8 @@
> #define INAT_VEXOK (1 << (INAT_FLAG_OFFS + 5))
> #define INAT_VEXONLY (1 << (INAT_FLAG_OFFS + 6))
> #define INAT_EVEXONLY (1 << (INAT_FLAG_OFFS + 7))
> +#define INAT_NO_REX2 (1 << (INAT_FLAG_OFFS + 8))
> +#define INAT_REX2_VARIANT (1 << (INAT_FLAG_OFFS + 9))
> /* Attribute making macros for attribute tables */
> #define INAT_MAKE_PREFIX(pfx) (pfx << INAT_PFX_OFFS)
> #define INAT_MAKE_ESCAPE(esc) (esc << INAT_ESC_OFFS)
> @@ -128,6 +132,11 @@ static inline int inat_is_rex_prefix(insn_attr_t attr)
> return (attr & INAT_PFX_MASK) == INAT_PFX_REX;
> }
>
> +static inline int inat_is_rex2_prefix(insn_attr_t attr)
> +{
> + return (attr & INAT_PFX_MASK) == INAT_PFX_REX2;
> +}
> +
> static inline int inat_last_prefix_id(insn_attr_t attr)
> {
> if ((attr & INAT_PFX_MASK) > INAT_LSTPFX_MAX)
> diff --git a/arch/x86/include/asm/insn.h b/arch/x86/include/asm/insn.h
> index 1b29f58f730f..95249ec1f24e 100644
> --- a/arch/x86/include/asm/insn.h
> +++ b/arch/x86/include/asm/insn.h
> @@ -112,10 +112,15 @@ struct insn {
> #define X86_SIB_INDEX(sib) (((sib) & 0x38) >> 3)
> #define X86_SIB_BASE(sib) ((sib) & 0x07)
>
> -#define X86_REX_W(rex) ((rex) & 8)
> -#define X86_REX_R(rex) ((rex) & 4)
> -#define X86_REX_X(rex) ((rex) & 2)
> -#define X86_REX_B(rex) ((rex) & 1)
> +#define X86_REX2_M(rex) ((rex) & 0x80) /* REX2 M0 */
> +#define X86_REX2_R(rex) ((rex) & 0x40) /* REX2 R4 */
> +#define X86_REX2_X(rex) ((rex) & 0x20) /* REX2 X4 */
> +#define X86_REX2_B(rex) ((rex) & 0x10) /* REX2 B4 */
> +
> +#define X86_REX_W(rex) ((rex) & 8) /* REX or REX2 W */
> +#define X86_REX_R(rex) ((rex) & 4) /* REX or REX2 R3 */
> +#define X86_REX_X(rex) ((rex) & 2) /* REX or REX2 X3 */
> +#define X86_REX_B(rex) ((rex) & 1) /* REX or REX2 B3 */
>
> /* VEX bit flags */
> #define X86_VEX_W(vex) ((vex) & 0x80) /* VEX3 Byte2 */
> @@ -161,6 +166,18 @@ static inline void insn_get_attribute(struct insn *insn)
> /* Instruction uses RIP-relative addressing */
> extern int insn_rip_relative(struct insn *insn);
>
> +static inline int insn_is_rex2(struct insn *insn)
> +{
> + if (!insn->prefixes.got)
> + insn_get_prefixes(insn);
> + return insn->rex_prefix.nbytes == 2;

It'd be nice to capture that a rex2 prefix is by definition 2 bytes.
Playing devil's advocate, if there were a REX and a REX2 prefix,
couldn't rex_prefix.nbytes be 3? I'm wondering about other prefix
combinations that may confuse this logic, maybe someone dreams up
doing this for say alignment reasons like "rep ret".

Thanks,
Ian

> +}
> +
> +static inline insn_byte_t insn_rex2_m_bit(struct insn *insn)
> +{
> + return X86_REX2_M(insn->rex_prefix.bytes[1]);
> +}
> +
> static inline int insn_is_avx(struct insn *insn)
> {
> if (!insn->prefixes.got)
> diff --git a/arch/x86/lib/insn.c b/arch/x86/lib/insn.c
> index 1bb155a0955b..6126ddc6e5f5 100644
> --- a/arch/x86/lib/insn.c
> +++ b/arch/x86/lib/insn.c
> @@ -185,6 +185,17 @@ int insn_get_prefixes(struct insn *insn)
> if (X86_REX_W(b))
> /* REX.W overrides opnd_size */
> insn->opnd_bytes = 8;
> + } else if (inat_is_rex2_prefix(attr)) {
> + insn_set_byte(&insn->rex_prefix, 0, b);
> + b = peek_nbyte_next(insn_byte_t, insn, 1);
> + insn_set_byte(&insn->rex_prefix, 1, b);
> + insn->rex_prefix.nbytes = 2;
> + insn->next_byte += 2;
> + if (X86_REX_W(b))
> + /* REX.W overrides opnd_size */
> + insn->opnd_bytes = 8;
> + insn->rex_prefix.got = 1;
> + goto vex_end;
> }
> }
> insn->rex_prefix.got = 1;
> @@ -294,6 +305,20 @@ int insn_get_opcode(struct insn *insn)
> goto end;
> }
>
> + /* Check if there is REX2 prefix or not */
> + if (insn_is_rex2(insn)) {
> + if (insn_rex2_m_bit(insn)) {
> + /* map 1 is escape 0x0f */
> + insn_attr_t esc_attr = inat_get_opcode_attribute(0x0f);
> +
> + pfx_id = insn_last_prefix_id(insn);
> + insn->attr = inat_get_escape_attribute(op, pfx_id, esc_attr);
> + } else {
> + insn->attr = inat_get_opcode_attribute(op);
> + }
> + goto end;
> + }
> +
> insn->attr = inat_get_opcode_attribute(op);
> while (inat_is_escape(insn->attr)) {
> /* Get escaped opcode */
> diff --git a/arch/x86/tools/gen-insn-attr-x86.awk b/arch/x86/tools/gen-insn-attr-x86.awk
> index af38469afd14..3f43aa7d8fef 100644
> --- a/arch/x86/tools/gen-insn-attr-x86.awk
> +++ b/arch/x86/tools/gen-insn-attr-x86.awk
> @@ -64,7 +64,9 @@ BEGIN {
>
> modrm_expr = "^([CDEGMNPQRSUVW/][a-z]+|NTA|T[012])"
> force64_expr = "\$[df]64\$"
> - rex_expr = "^REX(\\.[XRWB]+)*"
> + rex_expr = "^((REX(\\.[XRWB]+)+)|(REX$))"
> + rex2_expr = "\$REX2\$"
> + no_rex2_expr = "\$!REX2\$"
> fpu_expr = "^ESC" # TODO
>
> lprefix1_expr = "\$(66|!F3)\$"
> @@ -99,6 +101,7 @@ BEGIN {
> prefix_num["VEX+1byte"] = "INAT_PFX_VEX2"
> prefix_num["VEX+2byte"] = "INAT_PFX_VEX3"
> prefix_num["EVEX"] = "INAT_PFX_EVEX"
> + prefix_num["REX2"] = "INAT_PFX_REX2"
>
> clear_vars()
> }
> @@ -314,6 +317,10 @@ function convert_operands(count,opnd, i,j,imm,mod)
> if (match(ext, force64_expr))
> flags = add_flags(flags, "INAT_FORCE64")
>
> + # check REX2 not allowed
> + if (match(ext, no_rex2_expr))
> + flags = add_flags(flags, "INAT_NO_REX2")
> +
> # check REX prefix
> if (match(opcode, rex_expr))
> flags = add_flags(flags, "INAT_MAKE_PREFIX(INAT_PFX_REX)")
> @@ -351,6 +358,8 @@ function convert_operands(count,opnd, i,j,imm,mod)
> lptable3[idx] = add_flags(lptable3[idx],flags)
> variant = "INAT_VARIANT"
> }
> + if (match(ext, rex2_expr))
> + table[idx] = add_flags(table[idx], "INAT_REX2_VARIANT")
> if (!match(ext, lprefix_expr)){
> table[idx] = add_flags(table[idx],flags)
> }
> diff --git a/tools/arch/x86/include/asm/inat.h b/tools/arch/x86/include/asm/inat.h
> index a61051400311..2e65312cae52 100644
> --- a/tools/arch/x86/include/asm/inat.h
> +++ b/tools/arch/x86/include/asm/inat.h
> @@ -35,6 +35,8 @@
> #define INAT_PFX_VEX2 13 /* 2-bytes VEX prefix */
> #define INAT_PFX_VEX3 14 /* 3-bytes VEX prefix */
> #define INAT_PFX_EVEX 15 /* EVEX prefix */
> +/* x86-64 REX2 prefix */
> +#define INAT_PFX_REX2 16 /* 0xD5 */
>
> #define INAT_LSTPFX_MAX 3
> #define INAT_LGCPFX_MAX 11
> @@ -50,7 +52,7 @@
>
> /* Legacy prefix */
> #define INAT_PFX_OFFS 0
> -#define INAT_PFX_BITS 4
> +#define INAT_PFX_BITS 5
> #define INAT_PFX_MAX ((1 << INAT_PFX_BITS) - 1)
> #define INAT_PFX_MASK (INAT_PFX_MAX << INAT_PFX_OFFS)
> /* Escape opcodes */
> @@ -77,6 +79,8 @@
> #define INAT_VEXOK (1 << (INAT_FLAG_OFFS + 5))
> #define INAT_VEXONLY (1 << (INAT_FLAG_OFFS + 6))
> #define INAT_EVEXONLY (1 << (INAT_FLAG_OFFS + 7))
> +#define INAT_NO_REX2 (1 << (INAT_FLAG_OFFS + 8))
> +#define INAT_REX2_VARIANT (1 << (INAT_FLAG_OFFS + 9))
> /* Attribute making macros for attribute tables */
> #define INAT_MAKE_PREFIX(pfx) (pfx << INAT_PFX_OFFS)
> #define INAT_MAKE_ESCAPE(esc) (esc << INAT_ESC_OFFS)
> @@ -128,6 +132,11 @@ static inline int inat_is_rex_prefix(insn_attr_t attr)
> return (attr & INAT_PFX_MASK) == INAT_PFX_REX;
> }
>
> +static inline int inat_is_rex2_prefix(insn_attr_t attr)
> +{
> + return (attr & INAT_PFX_MASK) == INAT_PFX_REX2;
> +}
> +
> static inline int inat_last_prefix_id(insn_attr_t attr)
> {
> if ((attr & INAT_PFX_MASK) > INAT_LSTPFX_MAX)
> diff --git a/tools/arch/x86/include/asm/insn.h b/tools/arch/x86/include/asm/insn.h
> index 65c0d9ce1e29..1a7e8fc4d75a 100644
> --- a/tools/arch/x86/include/asm/insn.h
> +++ b/tools/arch/x86/include/asm/insn.h
> @@ -112,10 +112,15 @@ struct insn {
> #define X86_SIB_INDEX(sib) (((sib) & 0x38) >> 3)
> #define X86_SIB_BASE(sib) ((sib) & 0x07)
>
> -#define X86_REX_W(rex) ((rex) & 8)
> -#define X86_REX_R(rex) ((rex) & 4)
> -#define X86_REX_X(rex) ((rex) & 2)
> -#define X86_REX_B(rex) ((rex) & 1)
> +#define X86_REX2_M(rex) ((rex) & 0x80) /* REX2 M0 */
> +#define X86_REX2_R(rex) ((rex) & 0x40) /* REX2 R4 */
> +#define X86_REX2_X(rex) ((rex) & 0x20) /* REX2 X4 */
> +#define X86_REX2_B(rex) ((rex) & 0x10) /* REX2 B4 */
> +
> +#define X86_REX_W(rex) ((rex) & 8) /* REX or REX2 W */
> +#define X86_REX_R(rex) ((rex) & 4) /* REX or REX2 R3 */
> +#define X86_REX_X(rex) ((rex) & 2) /* REX or REX2 X3 */
> +#define X86_REX_B(rex) ((rex) & 1) /* REX or REX2 B3 */
>
> /* VEX bit flags */
> #define X86_VEX_W(vex) ((vex) & 0x80) /* VEX3 Byte2 */
> @@ -161,6 +166,18 @@ static inline void insn_get_attribute(struct insn *insn)
> /* Instruction uses RIP-relative addressing */
> extern int insn_rip_relative(struct insn *insn);
>
> +static inline int insn_is_rex2(struct insn *insn)
> +{
> + if (!insn->prefixes.got)
> + insn_get_prefixes(insn);
> + return insn->rex_prefix.nbytes == 2;
> +}
> +
> +static inline insn_byte_t insn_rex2_m_bit(struct insn *insn)
> +{
> + return X86_REX2_M(insn->rex_prefix.bytes[1]);
> +}
> +
> static inline int insn_is_avx(struct insn *insn)
> {
> if (!insn->prefixes.got)
> diff --git a/tools/arch/x86/lib/insn.c b/tools/arch/x86/lib/insn.c
> index ada4b4a79dd4..f761adeb8e8c 100644
> --- a/tools/arch/x86/lib/insn.c
> +++ b/tools/arch/x86/lib/insn.c
> @@ -185,6 +185,17 @@ int insn_get_prefixes(struct insn *insn)
> if (X86_REX_W(b))
> /* REX.W overrides opnd_size */
> insn->opnd_bytes = 8;
> + } else if (inat_is_rex2_prefix(attr)) {
> + insn_set_byte(&insn->rex_prefix, 0, b);
> + b = peek_nbyte_next(insn_byte_t, insn, 1);
> + insn_set_byte(&insn->rex_prefix, 1, b);
> + insn->rex_prefix.nbytes = 2;
> + insn->next_byte += 2;
> + if (X86_REX_W(b))
> + /* REX.W overrides opnd_size */
> + insn->opnd_bytes = 8;
> + insn->rex_prefix.got = 1;
> + goto vex_end;
> }
> }
> insn->rex_prefix.got = 1;
> @@ -294,6 +305,20 @@ int insn_get_opcode(struct insn *insn)
> goto end;
> }
>
> + /* Check if there is REX2 prefix or not */
> + if (insn_is_rex2(insn)) {
> + if (insn_rex2_m_bit(insn)) {
> + /* map 1 is escape 0x0f */
> + insn_attr_t esc_attr = inat_get_opcode_attribute(0x0f);
> +
> + pfx_id = insn_last_prefix_id(insn);
> + insn->attr = inat_get_escape_attribute(op, pfx_id, esc_attr);
> + } else {
> + insn->attr = inat_get_opcode_attribute(op);
> + }
> + goto end;
> + }
> +
> insn->attr = inat_get_opcode_attribute(op);
> while (inat_is_escape(insn->attr)) {
> /* Get escaped opcode */
> diff --git a/tools/arch/x86/tools/gen-insn-attr-x86.awk b/tools/arch/x86/tools/gen-insn-attr-x86.awk
> index af38469afd14..3f43aa7d8fef 100644
> --- a/tools/arch/x86/tools/gen-insn-attr-x86.awk
> +++ b/tools/arch/x86/tools/gen-insn-attr-x86.awk
> @@ -64,7 +64,9 @@ BEGIN {
>
> modrm_expr = "^([CDEGMNPQRSUVW/][a-z]+|NTA|T[012])"
> force64_expr = "\$[df]64\$"
> - rex_expr = "^REX(\\.[XRWB]+)*"
> + rex_expr = "^((REX(\\.[XRWB]+)+)|(REX$))"
> + rex2_expr = "\$REX2\$"
> + no_rex2_expr = "\$!REX2\$"
> fpu_expr = "^ESC" # TODO
>
> lprefix1_expr = "\$(66|!F3)\$"
> @@ -99,6 +101,7 @@ BEGIN {
> prefix_num["VEX+1byte"] = "INAT_PFX_VEX2"
> prefix_num["VEX+2byte"] = "INAT_PFX_VEX3"
> prefix_num["EVEX"] = "INAT_PFX_EVEX"
> + prefix_num["REX2"] = "INAT_PFX_REX2"
>
> clear_vars()
> }
> @@ -314,6 +317,10 @@ function convert_operands(count,opnd, i,j,imm,mod)
> if (match(ext, force64_expr))
> flags = add_flags(flags, "INAT_FORCE64")
>
> + # check REX2 not allowed
> + if (match(ext, no_rex2_expr))
> + flags = add_flags(flags, "INAT_NO_REX2")
> +
> # check REX prefix
> if (match(opcode, rex_expr))
> flags = add_flags(flags, "INAT_MAKE_PREFIX(INAT_PFX_REX)")
> @@ -351,6 +358,8 @@ function convert_operands(count,opnd, i,j,imm,mod)
> lptable3[idx] = add_flags(lptable3[idx],flags)
> variant = "INAT_VARIANT"
> }
> + if (match(ext, rex2_expr))
> + table[idx] = add_flags(table[idx], "INAT_REX2_VARIANT")
> if (!match(ext, lprefix_expr)){
> table[idx] = add_flags(table[idx],flags)
> }
> --
> 2.34.1
>

Next message: Moger, Babu: "Re: [RFC PATCH v3 17/17] x86/resctrl: Introduce interface to modify assignment states of the groups"
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