Sprinkle some annotations.

Let's define an ElfHeader type.

1 files changed, 104 insertions, 12 deletions

diff --git a/mkelf.lua b/mkelf.lua
index 94cde85..1c2687a 100644
--- a/mkelf.lua
+++ b/mkelf.lua
@@ -1,4 +1,7 @@
-local osabi = {
+local version <const> = 1
+
+---@enum Osabi
+local Osabi <const> = {
     sysv = 0x00,
     hpux = 0x01,
     netbsd = 0x02,
@@ -8,29 +11,118 @@ local osabi = {
     aix = 0x07,
     irix = 0x08,
     freebsd = 0x09,
-    tru64 = 0x0A,
-    modesto = 0x0B,
-    openbsd = 0x0C,
-    openvms = 0x0D,
-    nsk = 0x0E,
-    aros = 0x0F,
+    tru64 = 0x0a,
+    modesto = 0x0b,
+    openbsd = 0x0c,
+    openvms = 0x0d,
+    nsk = 0x0e,
+    aros = 0x0f,
     fenixos = 0x10,
     cloudabi = 0x11,
     opevos = 0x12,
 }
 
-local class = {
+---@enum Class
+local Class <const> = {
     bit32 = 0x1,
     bit64 = 0x2,
 }
 
-local endian = {
+---@enum Endian
+local Endian <const> = {
     little = 0x1,
     big = 0x2,
 }
 
-local version <const> = 1
+---@enum Type
+local Type <const> = {
+    none = 0x00,
+    rel = 0x01,
+    exec = 0x02,
+    dyn = 0x03,
+    core = 0x04,
+    loos = 0xfe00,
+    hios = 0xfeff,
+    loproc = 0xfe00,
+    hiproc = 0xfeff,
+}
+
+---@enum Machine
+local Machine <const> = {
+    none = 0x00,
+    att = 0x01,
+    sparc = 0x02,
+    x86 = 0x03,
+    m68k = 0x04,
+    m88k = 0x05,
+    -- todo
+}
+
+---@alias ElfMagic [integer, integer, integer, integer]
+---@class ElfHeader
+---@field magic ElfMagic
+---@field class Class
+---@field data Endian
+---@field version integer
+---@field osabi Osabi
+---@field abiversion integer
+---@field type Type
+---@field machine Machine
+
+---@type ElfHeader
+local header <const> = {
+    magic = { 0x7f, 0x45, 0x4c, 0x46 },
+    class = Class.bit32,
+    data = Endian.big,
+    version = version,
+    osabi = Osabi.netbsd,
+    abiversion = 0,
+    type = Type.exec,
+    machine = Machine.x86,
 
-local header = {
-    class = class["bit32"]
+    pack = function(self)
+        local ident = string.pack("BBBBBBBBBxxxxxxx",
+            self.magic[1], self.magic[2], self.magic[3], self.magic[4],
+            self.class,
+            self.data,
+            self.version,
+            self.osabi,
+            self.abiversion)
+        local e = (self.data == Endian.big) and ">" or "<"
+        local sz = (self.class == Class.bit64) and "I8" or "I4"
+        local hdr = string.pack(e .. "I2I2I4" ..
+            sz .. sz .. sz ..
+            "I4I2I2I2I2I2I2",
+            self.type,
+            self.machine,
+            self.version,
+            0,
+            0x34,
+            0xff,
+            0,
+            52,
+            0x20,
+            0,
+            0x28,
+            0,
+            0)
+        return ident .. hdr
+    end
 }
+
+local function main()
+    local output = "a.out"
+    for i in ipairs(arg) do
+        if arg[i] ~= "-o" then goto continue end
+        if not arg[i + 1] then
+            error("mkelf: missing filename after -o")
+        end
+        output = arg[i + 1]
+        ::continue::
+    end
+    local f = assert(io.open(output, "w"))
+    f:write(header:pack())
+    f:close()
+end
+
+main()