From cae9572cc1ddcffc0d449c7ae67e04695a0a67a8 Mon Sep 17 00:00:00 2001
From: Alex <enderice2@users.noreply.github.com>
Date: Thu, 20 Oct 2022 05:02:49 +0300
Subject: [PATCH] More work on system calls

---
 Architecture/amd64/SystemCalls.cpp            | 76 +++++++++++++++++--
 .../amd64/SystemCallsAssemblyStub.asm         | 54 +++++++++++++
 2 files changed, 124 insertions(+), 6 deletions(-)
 create mode 100644 Architecture/amd64/SystemCallsAssemblyStub.asm

diff --git a/Architecture/amd64/SystemCalls.cpp b/Architecture/amd64/SystemCalls.cpp
index 943c04d..f9607b4 100644
--- a/Architecture/amd64/SystemCalls.cpp
+++ b/Architecture/amd64/SystemCalls.cpp
@@ -4,18 +4,82 @@
 
 #include "cpu/gdt.hpp"
 
+// https://supercip971.github.io/02-wingos-syscalls.html
 using namespace CPU::x64;
 
-extern "C" __attribute__((naked, used, no_stack_protector)) void SystemCallHandlerStub()
-{
-}
-
+// "Core/SystemCalls.cpp"
 extern "C" uint64_t SystemCallsHandler(SyscallsRegs *regs);
 
+extern "C" void SystemCallHandlerStub();
+
+extern "C" __attribute__((naked, used, no_stack_protector)) void SystemCallHandlerStub_broken()
+{
+    // asmv(
+    //     // "cmp $0x08, 0x8(%rsp)\n"
+    //     //  "je 1f\n"
+    //     "swapgs\n"
+    //     //  "1:\n"
+
+    //     "mov %rsp, 0x8(%gs)\n" // CPUData->TempStack
+    //     "mov 0x0(%gs), %rsp\n" // CPUData->SystemCallStack
+    //     "push $0x1b\n"         // user data segment
+    //     "push 0x8(%gs)\n"      // saved stack
+    //     "push %r11\n"          // saved rflags
+    //     "push $0x23\n"         // user code segment
+    //     "push %rcx\n"          // Current RIP
+
+    //     "push %rax\n"
+    //     "push %rbx\n"
+    //     "push %rcx\n"
+    //     "push %rdx\n"
+    //     "push %rsi\n"
+    //     "push %rdi\n"
+    //     "push %rbp\n"
+    //     "push %r8\n"
+    //     "push %r9\n"
+    //     "push %r10\n"
+    //     "push %r11\n"
+    //     "push %r12\n"
+    //     "push %r13\n"
+    //     "push %r14\n"
+    //     "push %r15\n"
+
+    //     "mov %rsp, %rdi\n"
+    //     "mov $0, %rbp\n"
+    //     "call SystemCallsHandler\n"
+
+    //     "pop %r15\n"
+    //     "pop %r14\n"
+    //     "pop %r13\n"
+    //     "pop %r12\n"
+    //     "pop %r11\n"
+    //     "pop %r10\n"
+    //     "pop %r9\n"
+    //     "pop %r8\n"
+    //     "pop %rbp\n"
+    //     "pop %rdi\n"
+    //     "pop %rsi\n"
+    //     "pop %rdx\n"
+    //     "pop %rcx\n"
+    //     "pop %rbx\n"
+    //     /* "pop %rax\n" */
+
+    //     "mov 0x8(%gs), %rsp\n" // CPUData->TempStack
+
+    //     //  "cmp $0x08, 0x8(%rsp)\n"
+    //     //  "je 1f\n"
+    //     "swapgs\n"
+    //     //  "1:\n"
+
+    //     "sti\n"
+
+    //     "sysretq\n");
+}
+
 void InitializeSystemCalls()
 {
     wrmsr(MSR_EFER, rdmsr(MSR_EFER) | 1);
     wrmsr(MSR_STAR, ((uint64_t)(GDT_KERNEL_CODE) << 32) | ((uint64_t)(GDT_KERNEL_DATA | 3) << 48));
-    wrmsr(MSR_LSTAR, (uint64_t)SystemCallsHandler);
-    wrmsr(MSR_SYSCALL_MASK, 0);
+    wrmsr(MSR_LSTAR, (uint64_t)SystemCallHandlerStub);
+    wrmsr(MSR_SYSCALL_MASK, (uint64_t)(1 << 9));
 }
diff --git a/Architecture/amd64/SystemCallsAssemblyStub.asm b/Architecture/amd64/SystemCallsAssemblyStub.asm
new file mode 100644
index 0000000..610f8b5
--- /dev/null
+++ b/Architecture/amd64/SystemCallsAssemblyStub.asm
@@ -0,0 +1,54 @@
+[BITS 64]
+ALIGN	4096
+extern SystemCallsHandler
+global SystemCallHandlerStub
+SystemCallHandlerStub:
+    swapgs
+    mov [gs:0x8], rsp   ; CPUData->TempStack
+    mov rsp, [gs:0x0]   ; CPUData->SystemCallStack
+
+    push qword 0x23     ; user data segment
+    push qword [gs:0x8] ; saved stack
+    push r11            ; saved rflags
+    push qword 0x1b     ; user code segment
+    push rcx            ; Current RIP
+ 
+    push rax
+    push rbx
+    push rcx
+    push rdx
+    push rsi
+    push rdi
+    push rbp
+    push r8
+    push r9
+    push r10
+    push r11
+    push r12
+    push r13
+    push r14
+    push r15
+
+    mov rdi, rsp
+    mov rbp, 0
+    call SystemCallsHandler
+
+    pop r15
+    pop r14
+    pop r13
+    pop r12
+    pop r11
+    pop r10
+    pop r9
+    pop r8
+    pop rbp
+    pop rdi
+    pop rsi
+    pop rdx
+    pop rcx
+    pop rbx
+
+    mov rsp, [gs:0x8]
+    swapgs
+    sti
+    o64 sysret