From 7799813a305e34d287896f3fb9e25883c61c3be0 Mon Sep 17 00:00:00 2001
From: Lucia Ceionia <lucia@noreply.ceionius.com>
Date: Wed, 8 Feb 2023 11:38:35 -0600
Subject: [PATCH] Check for CMOV support on boot

---
 Makefile |  2 +-
 kernel.c | 13 +++++++++++++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index f94ab84..63efd2a 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,5 @@
 objects = entry.o kernel.o task.o handler.o interrupt.o v86.o print.o tss.o dosfs/dosfs.o gdt.o usermode.o paging.o fault.o tests.o kbd.o helper.o progs.o
-CFLAGS = -target "i486-elf" -m32 -mgeneral-regs-only -ffreestanding -march=pentium-m -fno-stack-protector -Wno-int-conversion -nostdlib -c
+CFLAGS = -target "i686-elf" -m32 -mgeneral-regs-only -ffreestanding -march=i686 -fno-stack-protector -Wno-int-conversion -nostdlib -c
 
 %.o: %.nasm
 	nasm -f elf32 -o $@ $<
diff --git a/kernel.c b/kernel.c
index ead2cf1..a4f0767 100644
--- a/kernel.c
+++ b/kernel.c
@@ -23,6 +23,11 @@ char check_sse() {
     asm("cpuid" : "=a"(eax), "=b"(ebx), "=c"(ecx), "=d"(edx) : "a"(1));
     return (edx & (1 << 25)) != 0;
 }
+char check_cmov() {
+    uint32_t eax, ebx, ecx, edx;
+    asm("cpuid" : "=a"(eax), "=b"(ebx), "=c"(ecx), "=d"(edx) : "a"(1));
+    return (edx & (1 << 15)) != 0;
+}
 
 void enable_sse() {
     asm volatile(
@@ -308,6 +313,14 @@ void start() {
     // DL *should* be preserved
     uint8_t dl;
     asm volatile("nop":"=d"(dl));
+
+    if (!check_cmov()) {
+        char cmov_err[] = "NO CMOV";
+        for (int i = 0; i < sizeof(cmov_err); i++)
+            *(char *)&vga_text[i] = cmov_err[i];
+        for (;;) asm volatile("hlt");
+    }
+
     vga_text += printByte(dl, vga_text);
     vga_text++;