From 4130562b1555cabe441efe9420cebe12e7ed8d39 Mon Sep 17 00:00:00 2001
From: Benji Dial <benji@benjidial.net>
Date: Sat, 13 Jan 2024 16:43:49 -0500
Subject: application loading

---
 documentation/syscalls.txt | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)
 create mode 100644 documentation/syscalls.txt

(limited to 'documentation/syscalls.txt')

diff --git a/documentation/syscalls.txt b/documentation/syscalls.txt
new file mode 100644
index 0000000..cbba5e3
--- /dev/null
+++ b/documentation/syscalls.txt
@@ -0,0 +1,27 @@
+on application entry:
+  there is a 1MiB - 8KiB area mapped writable and not
+  executable with guard pages on either side, and rsp is
+  set to the top of that. all other registers are set to 0.
+
+for all system calls:
+  rax, rdi, rsi, rdx are in/out paramters.
+  rbx, rbp, rsp, r12-r15 are preserved.
+  rcx, rflags, r8-r11 are clobbered.
+
+encode color:
+  rax in: 0
+  edi in: r + g * 256 + b * 65536
+  eax out: encoded color
+
+get framebuffer:
+  rax in: 1
+  rax out: pointer to framebuffer
+  rdi out: width + height * 2 ** 32
+  esi out: pitch
+  framebuffer is always 32 bpp. use the encode color syscall
+  to encode colors. pitch is in dwords, not in bytes.
+
+draw framebuffer:
+  rax in: 2
+  this draws changes to the framebuffer gotten by the get framebuffer
+  system call. (currently, the entire thing is copied, not just changes.)
-- 
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