Refactor header configuration handling.

- Mark optional fields and normalize them on load.
- Validate (work in progress) required fields and their values.
- Make sure that errors point to useful location in the config file.

3 files changed, 52 insertions, 27 deletions

diff --git a/elf/header.lua b/elf/header.lua
index 6baf327..b289f13 100644
--- a/elf/header.lua
+++ b/elf/header.lua
@@ -1,29 +1,63 @@
 local fmt = require("elf.fmt")
+local ec = require("elf.constants")
 
 ---@alias Magic [integer, integer, integer, integer]
 
 ---@class Header
----@field magic Magic
+---@field magic? Magic
 ---@field class Class
 ---@field data Endian
----@field ident_version integer
----@field osabi Osabi
----@field abiversion integer
+---@field ident_version? integer
+---@field osabi? Osabi
+---@field abiversion? integer
 ---@field type Type
 ---@field machine Machine
----@field version integer
----@field entry integer
----@field phoff integer
----@field shoff integer
----@field flags integer
----@field ehsize integer
+---@field version? integer
+---@field entry? integer
+---@field phoff? integer
+---@field shoff? integer
+---@field flags? integer
+---@field ehsize? integer
 ---@field phentsize? integer
 ---@field phnum? integer
----@field shentsize integer
----@field shnum integer
----@field shstrndx integer
+---@field shentsize? integer
+---@field shnum? integer
+---@field shstrndx? integer
 local M = {}
 
+function M.normalize(hdr)
+    hdr.magic = hdr.magic or { 0x7f, 0x45, 0x4c, 0x46 }
+    hdr.ident_version = hdr.ident_version or ec.VERSION
+    hdr.osabi = hdr.osabi or ec.Osabi.sysv
+    hdr.abiversion = hdr.abiversion or 0
+    hdr.version = hdr.version or ec.VERSION
+    hdr.entry = hdr.entry or 0
+    hdr.phoff = hdr.phoff or 0
+    hdr.shoff = hdr.shoff or 0
+    hdr.flags = hdr.flags or 0
+    hdr.ehsize = hdr.ehsize or 0
+    hdr.phentsize = hdr.phentsize or 0
+    hdr.phnum = hdr.phnum or 0
+    hdr.shentsize = hdr.shentsize or 0
+    hdr.shnum = hdr.shnum or 0
+    hdr.shstrndx = hdr.shstrndx or 0
+end
+
+function M.validate(hdr)
+    if not hdr.class then error("class is required in header", 3) end
+    if not hdr.data then error("data is required in header", 3) end
+    if not hdr.type then error("type is required in header", 3) end
+    if not hdr.machine then error("machine is required in header", 3) end
+
+    if hdr.class ~= ec.Class.bit32 and hdr.class ~= ec.Class.bit64 then
+        error("class must be Class.bit32 or Class.bit64 in header", 3)
+    end
+    if hdr.data ~= ec.Endian.little and hdr.data ~= ec.Endian.big then
+        error("data must be Endian.little or Endian.big in header", 3)
+    end
+    -- TODO additional validations
+end
+
 ---@param hdr Header
 ---@return string
 ---@nodiscard
diff --git a/mkelf.lua b/mkelf.lua
index 1140be2..af794a0 100644
--- a/mkelf.lua
+++ b/mkelf.lua
@@ -29,7 +29,11 @@ local function loadconfig(fn)
             SegmentFlags = elf.SegmentFlags,
             ELFVERSION = elf.VERSION,
 
-            header = function(t) header = setmetatable(t, header_mt) end,
+            header = function(t)
+                header = setmetatable(t, header_mt)
+                t:normalize()
+                t:validate()
+            end,
             segments = function(t) segments = setmetatable(t, segments_mt) end,
             sections = function(t) sections = setmetatable(t, sections_mt) end,
         },
diff --git a/sample.elf.lua b/sample.elf.lua
index f6b48d5..d37a7c5 100644
--- a/sample.elf.lua
+++ b/sample.elf.lua
@@ -1,21 +1,8 @@
 header {
-    magic = { 0x7f, 0x45, 0x4c, 0x46 },
     class = Class.bit64,
     data = Endian.big,
-    ident_version = ELFVERSION,
-    osabi = Osabi.netbsd,
-    abiversion = 0,
     type = Type.exec,
     machine = Machine.i386,
-    version = ELFVERSION,
-    entry = 0,
-    phoff = 0x40,
-    shoff = 0xff,
-    flags = 0,
-    ehsize = 64,
-    shentsize = 0x40,
-    shnum = 0,
-    shstrndx = 0,
 }
 
 segments {