From f2a2a09688421f2c532ab6f02527bf68f095407a Mon Sep 17 00:00:00 2001
From: iximeow <me@iximeow.net>
Date: Mon, 25 May 2026 17:32:57 +0000
Subject: j*cxz/pusha/popa alternate size forms

these all existed since forever but the library did not distinguish them
and did not provide prefix information for users to tell which had been
decoded.
---
 src/long_mode/behavior.rs | 12 ++++++++----
 src/long_mode/display.rs  | 12 ++++++++++--
 src/long_mode/mod.rs      | 22 +++++++++++++++++++++-
 3 files changed, 39 insertions(+), 7 deletions(-)

(limited to 'src/long_mode')

diff --git a/src/long_mode/behavior.rs b/src/long_mode/behavior.rs
index 3e1b4a7..478c07a 100644
--- a/src/long_mode/behavior.rs
+++ b/src/long_mode/behavior.rs
@@ -229,8 +229,7 @@ impl Instruction {
                 }
             } else if self.opcode() == Opcode::LOOPNZ
                 || self.opcode() == Opcode::LOOPZ
-                || self.opcode() == Opcode::LOOP
-                || self.opcode() == Opcode::JRCXZ {
+                || self.opcode() == Opcode::LOOP {
                if self.prefixes.rex_unchecked().w() {
                    behavior = behavior
                        .set_implicit_ops(RW_RCX_IDX);
@@ -3559,7 +3558,7 @@ fn behavior_table_size_is_right() {
 }
 
 /// this table MUST line up with Opcode declaration order in `mod.rs`.
-static TABLE: [BehaviorDigest; 1413] = [
+static TABLE: [BehaviorDigest; 1414] = [
     /* ADD => */ GENERAL_RW_R_FLAGWRITE,
     /* OR => */ GENERAL_RW_R_FLAGWRITE,
     /* ADC => */ GENERAL_RW_R_FLAGRW,
@@ -5167,7 +5166,7 @@ static TABLE: [BehaviorDigest; 1413] = [
     /* JRCXZ => */ BehaviorDigest::empty()
             .set_pl_any()
             .set_operand(0, Access::Read)
-            .set_nontrivial(true),
+            .set_implicit_ops(RW_RCX_IDX),
 
         // started shipping in Tremont, 2020 sept 23
         // while this instruction is marked "write, read", the written first operand is a register
@@ -5871,4 +5870,9 @@ static TABLE: [BehaviorDigest; 1413] = [
             .set_pl0()
             .set_flags_access(Access::Write)
             .set_complex(true),
+
+    /* JECXZ => */ BehaviorDigest::empty()
+            .set_pl_any()
+            .set_operand(0, Access::Read)
+            .set_implicit_ops(RW_ECX_IDX),
 ];
diff --git a/src/long_mode/display.rs b/src/long_mode/display.rs
index f215d07..a00dd22 100644
--- a/src/long_mode/display.rs
+++ b/src/long_mode/display.rs
@@ -2100,6 +2100,8 @@ const MNEMONICS: &[&'static str] = &[
     "pvalidate",
     "rmpadjust",
     "rmpupdate",
+
+    "jecxz",
 ];
 
 impl Opcode {
@@ -2699,6 +2701,7 @@ impl <T: fmt::Write, Y: YaxColors> Colorize<T, Y> for Opcode {
             Opcode::LOOPZ |
             Opcode::LOOP |
             Opcode::JRCXZ |
+            Opcode::JECXZ |
             Opcode::CALL |
             Opcode::CALLF |
             Opcode::JMP |
@@ -4018,6 +4021,10 @@ pub(crate) fn contextualize_c<T: DisplaySink>(instr: &Instruction, out: &mut T)
             out.write_str("if rcx == 0 then jmp ")?;
             write_jmp_operand(instr.operand(0), out)?;
         },
+        Opcode::JECXZ => {
+            out.write_str("if ecx == 0 then jmp ")?;
+            write_jmp_operand(instr.operand(0), out)?;
+        },
         Opcode::LOOP => {
             out.write_str("rcx--; if rcx != 0 then jmp ")?;
             write_jmp_operand(instr.operand(0), out)?;
@@ -4216,8 +4223,9 @@ impl <T: fmt::Write, Y: YaxColors> ShowContextual<u64, [Option<alloc::string::St
     }
 }
 
-static RELATIVE_BRANCHES: [Opcode; 22] = [
-    Opcode::JMP, Opcode::CALL, Opcode::JRCXZ,
+static RELATIVE_BRANCHES: [Opcode; 23] = [
+    Opcode::JMP, Opcode::CALL,
+    Opcode::JRCXZ, Opcode::JECXZ,
     Opcode::LOOP, Opcode::LOOPZ, Opcode::LOOPNZ,
     Opcode::JO, Opcode::JNO,
     Opcode::JB, Opcode::JNB,
diff --git a/src/long_mode/mod.rs b/src/long_mode/mod.rs
index c477b16..f2fac5b 100644
--- a/src/long_mode/mod.rs
+++ b/src/long_mode/mod.rs
@@ -2593,6 +2593,9 @@ pub enum Opcode {
     PVALIDATE,
     RMPADJUST,
     RMPUPDATE,
+
+    // this was present since initial x86-64 but the library missed the prefix handling..
+    JECXZ,
 }
 
 impl PartialEq for Instruction {
@@ -4047,6 +4050,7 @@ enum OperandCase {
     ModRM_0xf30f38fa,
     ModRM_0xf30f38fb,
     ModRM_0xf30f3af0,
+    CXZ,
 }
 
 #[allow(non_camel_case_types)]
@@ -4381,6 +4385,7 @@ enum OperandCode {
     Ev_G_xmm_Ib = OperandCodeBuilder::new().read_E().operand_case(OperandCase::Ev_G_xmm_Ib).bits(),
     G_E_mm_Ib = OperandCodeBuilder::new().read_E().operand_case(OperandCase::G_E_mm_Ib).bits(),
     MASKMOVDQU = OperandCodeBuilder::new().read_E().reg_mem().operand_case(OperandCase::MASKMOVDQU).bits(),
+    CXZ = OperandCodeBuilder::new().operand_case(OperandCase::CXZ).bits(),
 }
 
 fn base_opcode_map(v: u8) -> Opcode {
@@ -4684,7 +4689,7 @@ const OPCODES: [OpcodeRecord; 256] = [
     OpcodeRecord::new(Interpretation::Instruction(Opcode::LOOPNZ), OperandCode::Ibs),
     OpcodeRecord::new(Interpretation::Instruction(Opcode::LOOPZ), OperandCode::Ibs),
     OpcodeRecord::new(Interpretation::Instruction(Opcode::LOOP), OperandCode::Ibs),
-    OpcodeRecord::new(Interpretation::Instruction(Opcode::JRCXZ), OperandCode::Ibs),
+    OpcodeRecord::new(Interpretation::Instruction(Opcode::JRCXZ), OperandCode::CXZ),
     OpcodeRecord::new(Interpretation::Instruction(Opcode::IN), OperandCode::AL_Ib),
     OpcodeRecord::new(Interpretation::Instruction(Opcode::IN), OperandCode::AX_Ib),
     OpcodeRecord::new(Interpretation::Instruction(Opcode::OUT), OperandCode::Ib_AL),
@@ -9117,6 +9122,21 @@ fn read_operands<
                 instruction.regs[0].bank = RegisterBank::Q;
             };
         }
+        OperandCase::CXZ => {
+            if instruction.prefixes.address_size() {
+                // address-size overridden from 64-bit to 32-bit
+                instruction.opcode = Opcode::JECXZ;
+            }
+            instruction.imm =
+                read_imm_signed(words, 1)? as u64;
+            sink.record(
+                words.offset() as u32 * 8 - 8,
+                words.offset() as u32 * 8 - 1,
+                InnerDescription::Number("1-byte immediate", instruction.imm as i64)
+                    .with_id(words.offset() as u32 * 8),
+            );
+            instruction.operands[0] = OperandSpec::ImmI8;
+        },
     };
     Ok(())
 }
-- 
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