From a85dbc3c3f6f0ee2ac1190884f49737ee59bb2f8 Mon Sep 17 00:00:00 2001
From: Eduard Urbach <eduard@urbach.dev>
Date: Sun, 20 Jul 2025 12:42:53 +0200
Subject: [PATCH] Fixed syscall encoding on arm64 macs

---
 src/arm/Syscall.go      |  4 ++--
 src/arm/Syscall_test.go | 24 ++++++++++++++++++++++++
 src/arm/arm_test.go     |  1 -
 src/arm/encode.go       |  2 +-
 src/asm/compilerARM.go  |  8 +++++++-
 5 files changed, 34 insertions(+), 5 deletions(-)
 create mode 100644 src/arm/Syscall_test.go

diff --git a/src/arm/Syscall.go b/src/arm/Syscall.go
index 1617a9e..d4dea68 100644
--- a/src/arm/Syscall.go
+++ b/src/arm/Syscall.go
@@ -1,6 +1,6 @@
 package arm
 
 // Syscall is the primary way to communicate with the OS kernel.
-func Syscall() uint32 {
-	return 0xD4000001
+func Syscall(imm16 int) uint32 {
+	return 0b11010100000<<21 | uint32(imm16&mask16)<<5 | 0b00001
 }
\ No newline at end of file
diff --git a/src/arm/Syscall_test.go b/src/arm/Syscall_test.go
new file mode 100644
index 0000000..8c0db32
--- /dev/null
+++ b/src/arm/Syscall_test.go
@@ -0,0 +1,24 @@
+package arm_test
+
+import (
+	"testing"
+
+	"git.urbach.dev/cli/q/src/arm"
+	"git.urbach.dev/go/assert"
+)
+
+func TestSyscall(t *testing.T) {
+	usagePatterns := []struct {
+		Number int
+		Code   uint32
+	}{
+		{0, 0xD4000001},
+		{0xFFFF, 0xD41FFFE1},
+	}
+
+	for _, pattern := range usagePatterns {
+		t.Logf("svc %d", pattern.Number)
+		code := arm.Syscall(pattern.Number)
+		assert.Equal(t, code, pattern.Code)
+	}
+}
\ No newline at end of file
diff --git a/src/arm/arm_test.go b/src/arm/arm_test.go
index 100f2a6..dbc29d5 100644
--- a/src/arm/arm_test.go
+++ b/src/arm/arm_test.go
@@ -10,7 +10,6 @@ import (
 func TestConstants(t *testing.T) {
 	assert.DeepEqual(t, arm.Nop(), 0xD503201F)
 	assert.DeepEqual(t, arm.Return(), 0xD65F03C0)
-	assert.DeepEqual(t, arm.Syscall(), 0xD4000001)
 }
 
 func TestNotEncodable(t *testing.T) {
diff --git a/src/arm/encode.go b/src/arm/encode.go
index de5ddbb..d66737a 100644
--- a/src/arm/encode.go
+++ b/src/arm/encode.go
@@ -6,7 +6,7 @@ import (
 
 // memory encodes an instruction with a register, a base register, an addressing mode and an offset.
 func memory(destination cpu.Register, base cpu.Register, mode AddressMode, imm9 int) uint32 {
-	return uint32(imm9&mask9)<<12 | uint32(mode<<10) | uint32(base)<<5 | uint32(destination)
+	return uint32(imm9&mask9)<<12 | uint32(mode)<<10 | uint32(base)<<5 | uint32(destination)
 }
 
 // pair encodes an instruction using a register pair with memory.
diff --git a/src/asm/compilerARM.go b/src/asm/compilerARM.go
index 684bf11..5c870fe 100644
--- a/src/asm/compilerARM.go
+++ b/src/asm/compilerARM.go
@@ -5,6 +5,7 @@ import (
 	"fmt"
 
 	"git.urbach.dev/cli/q/src/arm"
+	"git.urbach.dev/cli/q/src/config"
 	"git.urbach.dev/cli/q/src/token"
 )
 
@@ -149,7 +150,12 @@ func (c *compilerARM) Compile(instr Instruction) {
 	case *StackFrameEnd:
 		c.append(arm.LoadRegister(arm.LR, arm.SP, arm.PostIndex, 16, 8))
 	case *Syscall:
-		c.append(arm.Syscall())
+		switch c.build.OS {
+		case config.Mac:
+			c.append(arm.Syscall(0xFFFF))
+		default:
+			c.append(arm.Syscall(0))
+		}
 	default:
 		panic("unknown instruction")
 	}
-- 
2.51.2