feat: TrueType (TTF) font rendering, many new desktop applications and DOOM support, among other improvements

kernel/src/Sched/Context.asm

@@ -1,18 +1,30 @@
 ;
 ;   Context.asm
-;   Context switch: save/restore callee-saved registers, stack pointer, and CR3
+;   Context switch: save/restore callee-saved registers, stack pointer, CR3, and FPU state
 ;   Copyright (c) 2025 Daniel Hammer
 ;
 
 [bits 64]
 section .text
 
-; void SchedContextSwitch(uint64_t* oldRsp, uint64_t newRsp, uint64_t newCR3)
+; void SchedContextSwitch(uint64_t* oldRsp, uint64_t newRsp, uint64_t newCR3,
+;                         uint8_t* oldFpuArea, uint8_t* newFpuArea)
 ;   rdi = pointer to save old RSP
 ;   rsi = new RSP to restore
 ;   rdx = new PML4 physical address (for CR3)
+;   rcx = old FPU state area (may be null)
+;   r8  = new FPU state area (may be null)
 global SchedContextSwitch
 SchedContextSwitch:
+    ; Save FPU state before pushing registers (rcx/r8 are caller-saved)
+    test rcx, rcx
+    jz .skip_fxsave
+    fxsave [rcx]
+.skip_fxsave:
+
+    ; Stash r8 in r9 (callee-saved registers will clobber r8 slot on stack)
+    mov r9, r8
+
     ; Save callee-saved registers on the current stack
     push rbp
     push rbx
@@ -42,4 +54,10 @@ SchedContextSwitch:
     pop rbx
     pop rbp
 
+    ; Restore FPU state
+    test r9, r9
+    jz .skip_fxrstor
+    fxrstor [r9]
+.skip_fxrstor:
+
     ret