[RFC][PATCH 2/2] x86/insn: Simplify for_each_insn_prefix()

[Peter Zijlstra <peterz@infradead.org>]

Use the new-found freedom of allowing variable declarions inside
for() to simplify the for_each_insn_prefix() iterator to no longer
need an external temporary.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 arch/x86/boot/compressed/sev-handle-vc.c |    3 +--
 arch/x86/include/asm/insn.h              |    5 ++---
 arch/x86/kernel/kprobes/core.c           |    3 +--
 arch/x86/kernel/uprobes.c                |    6 ++----
 arch/x86/lib/insn-eval.c                 |   12 +++++-------
 tools/arch/x86/include/asm/insn.h        |    5 ++---
 6 files changed, 13 insertions(+), 21 deletions(-)

--- a/arch/x86/boot/compressed/sev-handle-vc.c
+++ b/arch/x86/boot/compressed/sev-handle-vc.c
@@ -29,11 +29,10 @@
 bool insn_has_rep_prefix(struct insn *insn)
 {
 	insn_byte_t p;
-	int i;
 
 	insn_get_prefixes(insn);
 
-	for_each_insn_prefix(insn, i, p) {
+	for_each_insn_prefix(insn, p) {
 		if (p == 0xf2 || p == 0xf3)
 			return true;
 	}
--- a/arch/x86/include/asm/insn.h
+++ b/arch/x86/include/asm/insn.h
@@ -316,7 +316,6 @@ static inline int insn_offset_immediate(
 /**
  * for_each_insn_prefix() -- Iterate prefixes in the instruction
  * @insn: Pointer to struct insn.
- * @idx:  Index storage.
  * @prefix: Prefix byte.
  *
  * Iterate prefix bytes of given @insn. Each prefix byte is stored in @prefix
@@ -325,8 +324,8 @@ static inline int insn_offset_immediate(
  * Since prefixes.nbytes can be bigger than 4 if some prefixes
  * are repeated, it cannot be used for looping over the prefixes.
  */
-#define for_each_insn_prefix(insn, idx, prefix)	\
-	for (idx = 0; idx < ARRAY_SIZE(insn->prefixes.bytes) && (prefix = insn->prefixes.bytes[idx]) != 0; idx++)
+#define for_each_insn_prefix(insn, prefix)	\
+	for (int idx = 0; idx < ARRAY_SIZE(insn->prefixes.bytes) && (prefix = insn->prefixes.bytes[idx]) != 0; idx++)
 
 #define POP_SS_OPCODE 0x1f
 #define MOV_SREG_OPCODE 0x8e
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -141,7 +141,6 @@ bool can_boost(struct insn *insn, void *
 {
 	kprobe_opcode_t opcode;
 	insn_byte_t prefix;
-	int i;
 
 	if (search_exception_tables((unsigned long)addr))
 		return false;	/* Page fault may occur on this address. */
@@ -154,7 +153,7 @@ bool can_boost(struct insn *insn, void *
 	if (insn->opcode.nbytes != 1)
 		return false;
 
-	for_each_insn_prefix(insn, i, prefix) {
+	for_each_insn_prefix(insn, prefix) {
 		insn_attr_t attr;
 
 		attr = inat_get_opcode_attribute(prefix);
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -259,9 +259,8 @@ static volatile u32 good_2byte_insns[256
 static bool is_prefix_bad(struct insn *insn)
 {
 	insn_byte_t p;
-	int i;
 
-	for_each_insn_prefix(insn, i, p) {
+	for_each_insn_prefix(insn, p) {
 		insn_attr_t attr;
 
 		attr = inat_get_opcode_attribute(p);
@@ -1404,7 +1403,6 @@ static int branch_setup_xol_ops(struct a
 {
 	u8 opc1 = OPCODE1(insn);
 	insn_byte_t p;
-	int i;
 
 	if (insn_is_nop(insn))
 		goto setup;
@@ -1437,7 +1435,7 @@ static int branch_setup_xol_ops(struct a
 	 * Intel and AMD behavior differ in 64-bit mode: Intel ignores 66 prefix.
 	 * No one uses these insns, reject any branch insns with such prefix.
 	 */
-	for_each_insn_prefix(insn, i, p) {
+	for_each_insn_prefix(insn, p) {
 		if (p == 0x66)
 			return -ENOTSUPP;
 	}
--- a/arch/x86/lib/insn-eval.c
+++ b/arch/x86/lib/insn-eval.c
@@ -63,11 +63,10 @@ static bool is_string_insn(struct insn *
 bool insn_has_rep_prefix(struct insn *insn)
 {
 	insn_byte_t p;
-	int i;
 
 	insn_get_prefixes(insn);
 
-	for_each_insn_prefix(insn, i, p) {
+	for_each_insn_prefix(insn, p) {
 		if (p == 0xf2 || p == 0xf3)
 			return true;
 	}
@@ -92,13 +91,13 @@ bool insn_has_rep_prefix(struct insn *in
 static int get_seg_reg_override_idx(struct insn *insn)
 {
 	int idx = INAT_SEG_REG_DEFAULT;
-	int num_overrides = 0, i;
+	int num_overrides = 0;
 	insn_byte_t p;
 
 	insn_get_prefixes(insn);
 
 	/* Look for any segment override prefixes. */
-	for_each_insn_prefix(insn, i, p) {
+	for_each_insn_prefix(insn, p) {
 		insn_attr_t attr;
 
 		attr = inat_get_opcode_attribute(p);
@@ -1701,7 +1700,6 @@ bool insn_is_nop(struct insn *insn)
 	u8 sib = 0, sib_scale, sib_index, sib_base;
 	u8 p = 0, rep = 0;
 	u8 nrex, rex;
-	int i;
 
 	if ((nrex = insn->rex_prefix.nbytes)) {
 		rex = insn->rex_prefix.bytes[nrex-1];
@@ -1773,7 +1771,7 @@ bool insn_is_nop(struct insn *insn)
 	if (p == INAT_PFX_REPE)
 		rep = 1;
 
-	for_each_insn_prefix(insn, i, p) {
+	for_each_insn_prefix(insn, p) {
 		if (p == 0xf3) /* REPE */
 			rep = 1;
 	}
@@ -1836,7 +1834,7 @@ bool insn_is_nop(struct insn *insn)
 		if (sib && (sib_scale != 0 || sib_index != 4)) /* (%reg, %eiz, 1) */
 			return false;
 
-		for_each_insn_prefix(insn, i, p) {
+		for_each_insn_prefix(insn, p) {
 			if (p != 0x3e) /* DS */
 				return false;
 		}
--- a/tools/arch/x86/include/asm/insn.h
+++ b/tools/arch/x86/include/asm/insn.h
@@ -312,7 +312,6 @@ static inline int insn_offset_immediate(
 /**
  * for_each_insn_prefix() -- Iterate prefixes in the instruction
  * @insn: Pointer to struct insn.
- * @idx:  Index storage.
  * @prefix: Prefix byte.
  *
  * Iterate prefix bytes of given @insn. Each prefix byte is stored in @prefix
@@ -321,8 +320,8 @@ static inline int insn_offset_immediate(
  * Since prefixes.nbytes can be bigger than 4 if some prefixes
  * are repeated, it cannot be used for looping over the prefixes.
  */
-#define for_each_insn_prefix(insn, idx, prefix)	\
-	for (idx = 0; idx < ARRAY_SIZE(insn->prefixes.bytes) && (prefix = insn->prefixes.bytes[idx]) != 0; idx++)
+#define for_each_insn_prefix(insn, prefix)	\
+	for (int idx = 0; idx < ARRAY_SIZE(insn->prefixes.bytes) && (prefix = insn->prefixes.bytes[idx]) != 0; idx++)
 
 #define POP_SS_OPCODE 0x1f
 #define MOV_SREG_OPCODE 0x8e