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Merged
merged 1 commit into from
Jul 8, 2025
Merged

Development #4

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3 changes: 1 addition & 2 deletions Kernel/Kernel.c
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Original file line number Diff line number Diff line change
Expand Up @@ -121,7 +121,6 @@ void task2(void) {
return;
}
void task3(void) {
// Test syscall
asm volatile(
"mov $2, %%rax\n" // SYS_WRITE
"mov $1, %%rbx\n" // stdout
Expand All @@ -132,7 +131,7 @@ void task3(void) {
: "r"("Syscall test!")
: "rax", "rbx", "rcx", "r8"
);

while (1) {
PrintKernelAt("T3 syscall", 12, 0);
for(volatile int i = 0; i < 50000; i++);
Expand Down
9 changes: 6 additions & 3 deletions Kernel/Syscall.c
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Original file line number Diff line number Diff line change
Expand Up @@ -4,10 +4,13 @@
#include "Idt.h"
extern void SyscallEntry(void);
uint64_t SyscallHandler(uint64_t syscall_num, uint64_t arg1, uint64_t arg2, uint64_t arg3) {
Process* current = GetCurrentProcess();
switch (syscall_num) {
case SYS_EXIT:
// Terminate current process
GetCurrentProcess()->state = PROC_TERMINATED;
if (current) {
current->state = PROC_TERMINATED;
}
Schedule(); // Switch to next process
return 0;

Expand All @@ -32,7 +35,7 @@ uint64_t SyscallHandler(uint64_t syscall_num, uint64_t arg1, uint64_t arg2, uint
return 0;

case SYS_GETPID:
return GetCurrentProcess()->pid;
return current ? current->pid : -1;

default:
return -1;
Expand All @@ -41,5 +44,5 @@ uint64_t SyscallHandler(uint64_t syscall_num, uint64_t arg1, uint64_t arg2, uint

void SyscallInit(void) {
// Install syscall interrupt (0x80)
IdtSetGate(0x80, (uint64_t)SyscallEntry, 0x08, 0x8E);
IdtSetGate(0x80, (uint64_t)SyscallEntry, SYSCALL_INTERRUPT_VECTOR, IDT_INTERRUPT_GATE_KERNEL);
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💡 Verification agent

🧩 Analysis chain

Verify the symbolic constant usage is correct.

The use of symbolic constants is excellent for maintainability. However, there's a naming issue with SYSCALL_INTERRUPT_VECTOR - it's set to 0x08 which is actually the kernel code segment selector, not an interrupt vector.

Based on the retrieved learnings, the IdtSetGate parameters are correct:

  • 0x80 (interrupt vector)
  • SyscallEntry (handler address)
  • SYSCALL_INTERRUPT_VECTOR (0x08 - kernel code selector)
  • IDT_INTERRUPT_GATE_KERNEL (0x8E - gate flags)

The constant naming could be clearer. Please verify that the syscall setup works correctly with these constants:

🏁 Script executed:

#!/bin/bash
# Description: Verify syscall interrupt vector setup and usage
# Expected: Find consistent usage of 0x80 as interrupt vector and 0x08 as selector

echo "=== Searching for syscall interrupt vector usage ==="
rg -A 2 -B 2 "0x80|syscall.*interrupt" 

echo "=== Searching for IdtSetGate function calls ==="
rg -A 2 -B 2 "IdtSetGate"

echo "=== Searching for symbolic constants usage ==="
rg -A 2 -B 2 "SYSCALL_INTERRUPT_VECTOR|IDT_INTERRUPT_GATE_KERNEL"

Length of output: 21978

Rename SYSCALL_INTERRUPT_VECTOR to clarify its role as a segment selector

The parameters to IdtSetGate are:

  • 0x80 = interrupt vector
  • SyscallEntry = handler address
  • 0x08 = segment selector, not an interrupt vector
  • 0x8E = gate flags

Everything is wired up correctly, but the constant name is misleading. Please rename it and update its use:

  • Kernel/Syscall.h
-#define SYSCALL_INTERRUPT_VECTOR 0x08
+#define SYSCALL_SEGMENT_SELECTOR  0x08
  • Kernel/Syscall.c
-    IdtSetGate(0x80, (uint64_t)SyscallEntry, SYSCALL_INTERRUPT_VECTOR, IDT_INTERRUPT_GATE_KERNEL);
+    IdtSetGate(0x80, (uint64_t)SyscallEntry, SYSCALL_SEGMENT_SELECTOR,  IDT_INTERRUPT_GATE_KERNEL);
🤖 Prompt for AI Agents 
In Kernel/Syscall.c at line 47 and Kernel/Syscall.h, rename the constant
SYSCALL_INTERRUPT_VECTOR to a name that clearly indicates it is a segment
selector, such as SYSCALL_SEGMENT_SELECTOR. Update all references to this
constant in both files accordingly to reflect its true purpose as a segment
selector rather than an interrupt vector.

}
3 changes: 2 additions & 1 deletion Kernel/Syscall.h
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Original file line number Diff line number Diff line change
Expand Up @@ -8,7 +8,8 @@
#define SYS_WRITE 2
#define SYS_READ 3
#define SYS_GETPID 4

#define SYSCALL_INTERRUPT_VECTOR 0x08
#define IDT_INTERRUPT_GATE_KERNEL 0x8E
// System call handler
void SyscallInit(void);
uint64_t SyscallHandler(uint64_t syscall_num, uint64_t arg1, uint64_t arg2, uint64_t arg3);
Expand Down
2 changes: 1 addition & 1 deletion meson.build
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Original file line number Diff line number Diff line change
Expand Up @@ -101,5 +101,5 @@ iso = custom_target('VoidFrame.iso',

# Run target
run_target('run',
command : ['qemu-system-x86_64', '-cdrom', iso, '-m', '1G']
command : ['qemu-system-x86_64', '-cdrom', 'VoidFrame.iso', '-m', '1G']
)