Initial Commit

src/syscall/syscall.c

@@ -0,0 +1,76 @@
+#include <stdint.h>
+#include "stdio.h"
+#include "fs/vfs.h"
+
+#define MSR_EFER   0xC0000080
+#define MSR_STAR   0xC0000081
+#define MSR_LSTAR  0xC0000082
+#define MSR_SFMASK 0xC0000084
+
+#define EFER_SCE (1 << 0)
+
+static inline void wrmsr(uint32_t msr, uint64_t value)
+{
+    uint32_t lo = value & 0xFFFFFFFF;
+    uint32_t hi = value >> 32;
+
+    asm volatile("wrmsr"
+                 :
+                 : "c"(msr), "a"(lo), "d"(hi));
+}
+
+static inline uint64_t rdmsr(uint32_t msr)
+{
+    uint32_t lo, hi;
+    asm volatile("rdmsr"
+                 : "=a"(lo), "=d"(hi)
+                 : "c"(msr));
+    return ((uint64_t)hi << 32) | lo;
+}
+
+void syscall_handler(uint64_t rax, // syscall num
+                     uint64_t rdi, // arg1
+                     uint64_t rsi, // arg2
+                     uint64_t rdx, // arg3
+                     uint64_t r10, // arg4
+                     uint64_t r8,  // arg5
+                     uint64_t r9)  // arg6
+{
+    switch (rax)
+    {
+        case 1: // write (int fd, const void *buf, size_t count);
+            int c = (char)rdi;
+            printf("%c", c);
+            break;
+
+        case 2:
+            // exit
+            break;
+
+        default:
+            break;
+    }
+}
+
+void syscall_init(void)
+{
+    extern void syscall_entry(void);
+
+    uint64_t kernel_cs = 0x08;
+    uint64_t user_cs   = 0x1B;
+
+    uint64_t star =
+        ((uint64_t)kernel_cs << 32) |
+        ((uint64_t)user_cs << 48);
+
+    wrmsr(MSR_STAR, star);
+
+    wrmsr(MSR_LSTAR, (uint64_t)syscall_entry);
+
+    uint64_t efer = rdmsr(MSR_EFER);
+    efer |= (1 << 0); // SYSCALL/SYSRET enable
+    wrmsr(MSR_EFER, efer);
+
+    // disable interrupts on syscall entry
+    wrmsr(MSR_SFMASK, (1 << 9));
+}