Add x86 syscalls

src/kernel/arch/x86/arch.zig

@@ -7,6 +7,7 @@ const irq = @import("irq.zig");
 const isr = @import("isr.zig");
 const log = @import("../../log.zig");
 const pit = @import("pit.zig");
+const syscalls = @import("syscalls.zig");
 
 pub const InterruptContext = struct {
     // Extra segments
@@ -58,6 +59,8 @@ pub fn init(mem_profile: *const MemProfile, allocator: *std.mem.Allocator, compt
 
     paging.init(mem_profile, allocator);
 
+    syscalls.init(options);
+
     // Enable interrupts
     enableInterrupts();
 }

src/kernel/arch/x86/isr.zig

@@ -3,6 +3,7 @@
 const panic = @import("../../panic.zig");
 const idt = @import("idt.zig");
 const arch = @import("arch.zig");
+const syscalls = @import("syscalls.zig");
 
 const NUMBER_OF_ENTRIES: u16 = 32;
 
@@ -39,6 +40,7 @@ extern fn isr28() void;
 extern fn isr29() void;
 extern fn isr30() void;
 extern fn isr31() void;
+extern fn isr128() void;
 
 /// The exception messaged that is printed when a exception happens
 const exception_msg: [NUMBER_OF_ENTRIES][]const u8 = [NUMBER_OF_ENTRIES][]const u8 {
@@ -76,8 +78,18 @@ const exception_msg: [NUMBER_OF_ENTRIES][]const u8 = [NUMBER_OF_ENTRIES][]const
     "Reserved"
 };
 
+/// Errors that an isr function can return
+pub const IsrError = error {
+    UnrecognisedIsr
+};
+
+/// An isr handler. Takes an interrupt context and returns void.
+/// Should finish quickly to avoid delaying further interrupts and the previously running code
+pub const IsrHandler = fn(*arch.InterruptContext)void;
+
 // The of exception handlers initialised to unhandled.
-var isr_handlers: [NUMBER_OF_ENTRIES]fn(*arch.InterruptContext)void = []fn(*arch.InterruptContext)void{unhandled} ** NUMBER_OF_ENTRIES;
+var isr_handlers: [NUMBER_OF_ENTRIES]IsrHandler = []IsrHandler{unhandled} ** NUMBER_OF_ENTRIES;
+var syscall_handler: IsrHandler = unhandled;
 
 ///
 /// A dummy handler that will make a call to panic as it is a unhandled exception.
@@ -91,6 +103,17 @@ fn unhandled(context: *arch.InterruptContext) void {
     panic.panicFmt(null, "Unhandled exception: {}, number {}", exception_msg[interrupt_num], interrupt_num);
 }
 
+///
+/// Checks if the isr is valid and returns true if it is, else false.
+/// To be valid it must be greater than or equal to 0 and less than NUMBER_OF_ENTRIES.
+///
+/// Arguments:
+///     IN isr_num: u16 - The isr number to check
+///
+pub fn isValidIsr(isr_num: u32) bool {
+    return isr_num >= 0 and isr_num < NUMBER_OF_ENTRIES;
+}
+
 ///
 /// The exception handler that each of the exceptions will call when a exception happens.
 ///
@@ -100,7 +123,13 @@ fn unhandled(context: *arch.InterruptContext) void {
 ///
 export fn isrHandler(context: *arch.InterruptContext) void {
     const isr_num = context.int_num;
+    if (isr_num == syscalls.INTERRUPT) {
+        syscall_handler(context);
+    } else if (isValidIsr(isr_num)) {
         isr_handlers[isr_num](context);
+    } else {
+        panic.panicFmt(null, "Unrecognised isr: {}\n", isr_num);
+    }
 }
 
 ///
@@ -109,8 +138,17 @@ export fn isrHandler(context: *arch.InterruptContext) void {
 /// Arguments:
 ///     IN irq_num: u16 - The exception number to register.
 ///
-pub fn registerIsr(isr_num: u16, handler: fn(*arch.InterruptContext)void) void {
+/// Errors:
+///     IsrError.UnrecognisedIsr - If `isr_num` is invalid (see isValidIsr)
+///
+pub fn registerIsr(isr_num: u16, handler: fn(*arch.InterruptContext)void) !void {
+    if (isr_num == syscalls.INTERRUPT) {
+        syscall_handler = handler;
+    } else if (isValidIsr(isr_num)) {
         isr_handlers[isr_num] = handler;
+    } else {
+        return IsrError.UnrecognisedIsr;
+    }
 }
 
 ///
@@ -160,4 +198,5 @@ pub fn init() void {
     idt.openInterruptGate(29, isr29);
     idt.openInterruptGate(30, isr30);
     idt.openInterruptGate(31, isr31);
+    idt.openInterruptGate(syscalls.INTERRUPT, isr128);
 }

src/kernel/arch/x86/isr_asm.s

@@ -87,3 +87,4 @@ isrGenerator 28
 isrGenerator 29
 isrGenerator 30
 isrGenerator 31
+isrGenerator 128

src/kernel/arch/x86/paging.zig

@@ -142,7 +142,7 @@ pub fn init(mem_profile: *const MemProfile, allocator: *std.mem.Allocator) void
     mapDir(kernel_directory, p_start, p_end, v_start, v_end, allocator) catch unreachable;
     const dir_physaddr = @ptrToInt(kernel_directory) - constants.KERNEL_ADDR_OFFSET;
     asm volatile ("mov %[addr], %%cr3" :: [addr] "{eax}" (dir_physaddr));
-    isr.registerIsr(14, pageFault);
+    isr.registerIsr(14, pageFault) catch unreachable;
 }
 
 test "isAligned" {

src/kernel/arch/x86/syscalls.zig

@@ -0,0 +1,287 @@
+const arch = @import("arch.zig");
+const testing = @import("std").testing;
+const assert = @import("std").debug.assert;
+const isr = @import("isr.zig");
+const log = @import("../../log.zig");
+
+/// The isr number associated with syscalls
+pub const INTERRUPT: u16 = 0x80;
+
+/// The maximum number of syscall handlers that can be registered
+pub const NUM_HANDLERS: u16 = 256;
+
+/// A syscall handler
+pub const SyscallHandler = fn (ctx: *arch.InterruptContext) u32;
+
+/// Errors that syscall utility functions can throw
+pub const SyscallError = error {
+    SyscallExists,
+    InvalidSyscall
+};
+
+/// The array of registered syscalls
+var handlers: [NUM_HANDLERS]?SyscallHandler = []?SyscallHandler{null} ** NUM_HANDLERS;
+
+///
+/// Returns true if the syscall is valid, else false.
+/// A syscall is valid if it's less than NUM_HANDLERS.
+///
+/// Arguments:
+///     IN syscall: u32 - The syscall to check
+///
+pub fn isValidSyscall(syscall: u32) bool {
+    return syscall < NUM_HANDLERS;
+}
+
+///
+/// Handle a syscall. Gets the syscall number from eax within the context and calls the registered handler.
+/// If there isn't a registered handler or the syscall is invalid (>= NUM_HANDLERS) then a warning is logged.
+///
+/// Arguments:
+///     IN ctx: *arch.InterruptContext - The cpu context when the syscall was triggered. The syscall number is
+///                                      stored in eax.
+///
+fn handle(ctx: *arch.InterruptContext) void {
+    // The syscall number is put in eax
+    const syscall = ctx.eax;
+    if (isValidSyscall(syscall)) {
+        if (handlers[syscall]) |handler| {
+            ctx.eax = handler(ctx);
+        } else {
+            log.logWarning("Syscall {} triggered but not registered\n", syscall);
+        }
+    } else {
+        log.logWarning("Syscall {} is invalid\n", syscall);
+    }
+}
+
+///
+/// Register a syscall so it can be called by triggering interrupt 128.
+///
+/// Arguments:
+///     IN syscall: u8 - The syscall number to register the handler with.
+///     IN handler: SyscallHandler - The handler to register the syscall with.
+///
+/// Errors:
+///     SyscallError.InvalidSyscall - If the syscall is invalid (see isValidSyscall).
+///     SyscallError.SyscallExists - If the syscall has already been registered.
+///
+pub fn registerSyscall(syscall: u8, handler: SyscallHandler) SyscallError!void {
+    if (!isValidSyscall(syscall))
+        return SyscallError.InvalidSyscall;
+    if (handlers[syscall]) |_|
+        return SyscallError.SyscallExists;
+    handlers[syscall] = handler;
+}
+
+///
+/// Trigger a syscall with no arguments. Returns the value put in eax by the syscall.
+///
+/// Arguments:
+///     IN syscall: u32 - The syscall to trigger, put in eax.
+///
+inline fn syscall0(syscall: u32) u32 {
+    return asm volatile (
+        \\int $0x80
+        : [ret] "={eax}" (-> u32)
+        : [syscall] "{eax}" (syscall),
+    );
+}
+
+///
+/// Trigger a syscall with one argument. Returns the value put in eax by the syscall.
+///
+/// Arguments:
+///     IN syscall: u32 - The syscall to trigger, put in eax.
+///     IN arg: u32 - The argument to pass. Put in ebx.
+///
+inline fn syscall1(syscall: u32, arg: u32) u32 {
+    return asm volatile (
+        \\int $0x80
+        : [ret] "={eax}" (-> u32)
+        : [syscall] "{eax}" (syscall),
+          [arg1] "{ebx}" (arg),
+    );
+}
+
+///
+/// Trigger a syscall with two arguments. Returns the value put in eax by the syscall.
+///
+/// Arguments:
+///     IN syscall: u32 - The syscall to trigger, put in eax.
+///     IN arg1: u32 - The first argument to pass. Put in ebx.
+///     IN arg2: u32 - The second argument to pass. Put in ecx.
+///
+inline fn syscall2(syscall: u32, arg1: u32, arg2: u32) u32 {
+    return asm volatile (
+        \\int $0x80
+        : [ret] "={eax}" (-> u32)
+        : [syscall] "{eax}" (syscall),
+          [arg1] "{ebx}" (arg1),
+          [arg2] "{ecx}" (arg2),
+    );
+}
+
+///
+/// Trigger a syscall with three arguments. Returns the value put in eax by the syscall.
+///
+/// Arguments:
+///     IN syscall: u32 - The syscall to trigger, put in eax.
+///     IN arg1: u32 - The first argument to pass. Put in ebx.
+///     IN arg2: u32 - The second argument to pass. Put in ecx.
+///     IN arg3: u32 - The third argument to pass. Put in edx.
+///
+inline fn syscall3(syscall: u32, arg1: u32, arg2: u32, arg3: u32) u32 {
+    return asm volatile (
+        \\int $0x80
+        : [ret] "={eax}" (-> u32)
+        : [syscall] "{eax}" (syscall),
+          [arg1] "{ebx}" (arg1),
+          [arg2] "{ecx}" (arg2),
+          [arg3] "{edx}" (arg3),
+    );
+}
+
+///
+/// Trigger a syscall with four arguments. Returns the value put in eax by the syscall.
+///
+/// Arguments:
+///     IN syscall: u32 - The syscall to trigger, put in eax.
+///     IN arg1: u32 - The first argument to pass. Put in ebx.
+///     IN arg2: u32 - The second argument to pass. Put in ecx.
+///     IN arg3: u32 - The third argument to pass. Put in edx.
+///     IN arg4: u32 - The fourth argument to pass. Put in esi.
+///
+inline fn syscall4(syscall: u32, arg1: u32, arg2: u32, arg3: u32, arg4: u32) u32 {
+    return asm volatile (
+        \\int $0x80
+        : [ret] "={eax}" (-> u32)
+        : [syscall] "{eax}" (syscall),
+          [arg1] "{ebx}" (arg1),
+          [arg2] "{ecx}" (arg2),
+          [arg3] "{edx}" (arg3),
+          [arg4] "{esi}" (arg4),
+    );
+}
+
+///
+/// Trigger a syscall with five arguments. Returns the value put in eax by the syscall.
+///
+/// Arguments:
+///     IN syscall: u32 - The syscall to trigger, put in eax.
+///     IN arg1: u32 - The first argument to pass. Put in ebx.
+///     IN arg2: u32 - The second argument to pass. Put in ecx.
+///     IN arg3: u32 - The third argument to pass. Put in edx.
+///     IN arg4: u32 - The fourth argument to pass. Put in esi.
+///     IN arg5: u32 - The fifth argument to pass. Put in edi.
+///
+inline fn syscall5(syscall: u32, arg1: u32, arg2: u32, arg3: u32, arg4: u32, arg5: u32) u32 {
+    return asm volatile (
+        \\int $0x80
+        : [ret] "={eax}" (-> u32)
+        : [syscall] "{eax}" (syscall),
+          [arg1] "{ebx}" (arg1),
+          [arg2] "{ecx}" (arg2),
+          [arg3] "{edx}" (arg3),
+          [arg4] "{esi}" (arg4),
+          [arg5] "{edi}" (arg5),
+    );
+}
+
+///
+/// Gets the syscall argument according to the given index. 0 => ebx, 1 => ecx, 2 => edx, 3 => esi and 4 => edi.
+///
+/// Arguments:
+///     IN ctx: *arch.InterruptContext - The interrupt context from which to get the argument
+///     IN arg_idx: comptime u32 - The argument index to get. Between 0 and 4.
+///
+inline fn syscallArg(ctx: *arch.InterruptContext, comptime arg_idx: u32) u32 {
+    return switch (arg_idx) {
+        0 => ctx.ebx,
+        1 => ctx.ecx,
+        2 => ctx.edx,
+        3 => ctx.esi,
+        4 => ctx.edi,
+        else => @compileError("Arg index must be between 0 and 4")
+    };
+}
+
+///
+/// Initialise syscalls. Registers the isr associated with INTERRUPT.
+///
+pub fn init(comptime options: type) void {
+    log.logInfo("Init syscalls\n");
+    isr.registerIsr(INTERRUPT, handle) catch unreachable;
+    log.logInfo("Done\n");
+    if (options.rt_test) runtimeTests();
+}
+
+/// Tests
+
+var testInt: u32 = 0;
+
+fn testHandler0(ctx: *arch.InterruptContext) u32 {
+    testInt += 1;
+    return 0;
+}
+
+fn testHandler1(ctx: *arch.InterruptContext) u32 {
+    testInt += syscallArg(ctx, 0);
+    return 1;
+}
+
+fn testHandler2(ctx: *arch.InterruptContext) u32 {
+    testInt += syscallArg(ctx, 1);
+    return testHandler1(ctx) + 1;
+}
+
+fn testHandler3(ctx: *arch.InterruptContext) u32 {
+    testInt += syscallArg(ctx, 2);
+    return testHandler2(ctx) + 1;
+}
+
+fn testHandler4(ctx: *arch.InterruptContext) u32 {
+    testInt += syscallArg(ctx, 3);
+    return testHandler3(ctx) + 1;
+}
+
+fn testHandler5(ctx: *arch.InterruptContext) u32 {
+    testInt += syscallArg(ctx, 4);
+    return testHandler4(ctx) + 1;
+}
+
+test "registerSyscall returns SyscallExists" {
+    registerSyscall(123, testHandler) catch unreachable;
+    registerSyscall(123, testHandler) catch |err| {
+        return;
+    };
+    assert(false);
+}
+
+fn runtimeTests() void {
+    registerSyscall(123, testHandler0) catch unreachable;
+    registerSyscall(124, testHandler1) catch unreachable;
+    registerSyscall(125, testHandler2) catch unreachable;
+    registerSyscall(126, testHandler3) catch unreachable;
+    registerSyscall(127, testHandler4) catch unreachable;
+    registerSyscall(128, testHandler5) catch unreachable;
+    assert(testInt == 0);
+
+    if (syscall0(123) == 0 and testInt == 1)
+        log.logInfo("Syscalls: Tested no args\n");
+
+    if (syscall1(124, 2) == 1 and testInt == 3)
+        log.logInfo("Syscalls: Tested 1 arg\n");
+
+    if (syscall2(125, 2, 3) == 2 and testInt == 8)
+        log.logInfo("Syscalls: Tested 2 args\n");
+
+    if (syscall3(126, 2, 3, 4) == 3 and testInt == 17)
+        log.logInfo("Syscalls: Tested 3 args\n");
+
+    if (syscall4(127, 2, 3, 4, 5) == 4 and testInt == 31)
+        log.logInfo("Syscalls: Tested 4 args\n");
+
+    if (syscall5(128, 2, 3, 4, 5, 6) == 5 and testInt == 51)
+        log.logInfo("Syscalls: Tested 5 args\n");
+}

test/kernel/arch/x86/rt-test.py

@@ -2,5 +2,7 @@ def getTestCases(TestCase):
     return [
             TestCase("GDT init", [r"Init gdt", r"Done"]),
             TestCase("IDT init", [r"Init idt", r"Done"]),
-            TestCase("PIT init", [r"Init pit", r".+", "Done"])
+            TestCase("PIT init", [r"Init pit", r".+", "Done"]),
+            TestCase("Syscalls init", [r"Init syscalls", "Done"]),
+            TestCase("Syscall tests", [r"Syscalls: Tested no args", r"Syscalls: Tested 1 arg", r"Syscalls: Tested 2 args", r"Syscalls: Tested 3 args", r"Syscalls: Tested 4 args", r"Syscalls: Tested 5 args"])
         ]