From 786a195f8e81d4f7c0af2a82b9d458361d424a71 Mon Sep 17 00:00:00 2001
From: johannst <johannes.stoelp@gmail.com>
Date: Wed, 26 May 2021 00:21:06 +0200
Subject: minimal KVM abstraction + real mode guest example

---
 guest/Makefile  |  8 ++++++++
 guest/guest.ld  |  9 +++++++++
 guest/guest16.S | 21 +++++++++++++++++++++
 3 files changed, 38 insertions(+)
 create mode 100644 guest/Makefile
 create mode 100644 guest/guest.ld
 create mode 100644 guest/guest16.S

(limited to 'guest')

diff --git a/guest/Makefile b/guest/Makefile
new file mode 100644
index 0000000..e3f1e1b
--- /dev/null
+++ b/guest/Makefile
@@ -0,0 +1,8 @@
+guest16: guest.ld guest16.S
+	$(CC) $(CFLAGS) -m16 -o $@ -nostdlib -ffreestanding -Wpedantic -Wall -Wextra -Werror -T guest.ld guest16.S
+
+disasm: guest16
+	objdump -D -b binary -m i8086 -M intel $^
+
+clean:
+	$(RM) guest16
diff --git a/guest/guest.ld b/guest/guest.ld
new file mode 100644
index 0000000..5c81da9
--- /dev/null
+++ b/guest/guest.ld
@@ -0,0 +1,9 @@
+OUTPUT_FORMAT(binary)
+
+SECTIONS {
+    .boot     : { *(.boot) }
+    .text     : { *(.text) }
+    .data     : { *(.data) }
+    .rodata   : { *(.rodata) }
+    /DISCARD/ : { *(.*) }
+}
diff --git a/guest/guest16.S b/guest/guest16.S
new file mode 100644
index 0000000..7f0be0e
--- /dev/null
+++ b/guest/guest16.S
@@ -0,0 +1,21 @@
+.code16
+.intel_syntax noprefix
+
+.section .boot, "ax", @progbits
+    // Trigger `KVM_EXIT_IO:KVM_EXIT_IO_OUT` by writing string to output port.
+    mov dx, 0x1000          // Output port.
+    lea si, [msg]           // Address of string.
+    mov cx, [msg_len]       // Len of string.
+    rep outsb dx, ds:[si]   // Write out string bytes.
+
+    // Trigger `KVM_EXIT_MMIO` by writing to non mapped physical address.
+    mov byte ptr ds:[0x2000], 0xaa
+
+    // Trigger `KVM_EXIT_HLT`.
+    hlt
+
+.section .rodata, "a", @progbits
+msg:
+    .asciz "Hello from Real Mode!\n"
+msg_len:
+    .byte .-msg
-- 
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