Initial binary object layout spec and matching impl (sans code)

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

vm.md

@@ -195,6 +195,74 @@ wrapping around to 0.
 * Pop
 * More immediate stores?
 
+# Binary format
+
+The binary format is composed of a header followed by sections that make up the content of the blob.
+
+## Header
+
+The header is composed of:
+
+* 64 bits - A magic number (0xDEAD_BEA7_BA5E_BA11).
+* 16 bits - Version of the file
+* 16 bits - The number of sections in the file
+* 32 bits - Unused
+* section descriptions detailed below
+
+Total length: 128 bits
+
+## Sections
+
+The rest of the content is a list of sections. A section's layout is a section header, followed by
+the section contents.
+
+### Section header
+
+* 8 bits - Section kind
+    * 0x00 - Data
+    * 0x10 - Code
+    * 0xFF - Meta
+* 24 bits - Unused
+* 32 bits - Checksum of the section
+* 64 bits - Length of the section
+
+Total length: 128 bits
+
+### Data section
+
+The data section contains static data that is initialized to some known value.
+
+* 64 bits - load location - where in memory the contents of this section are put.
+
+### Code section
+
+The code section contains executable code.
+
+* 64 bits - load location - where in memory the contents of this section are put.
+
+The remaining length of the section is the code itself.
+
+### Meta section
+
+The meta section holds a table of metadata about the binary in a key-value format of strings mapping
+to other strings. All strings are UTF-8 encoded.
+
+* 64 bits - the number of key-value entries
+
+The remaining length of the section are the key-value pairs.
+
+The layout for a key-value pair is the key, followed immediately by the value. The key is always a
+string, and the value may be any type of data. A key starts with the length of the string, followed
+by the key string itself. A value starts with the length of the data, followed by the value data
+itself.
+
+The meta section should be used to place data that's readable by the VM, but is not used by the
+executing program. Data in the meta section is not copied to the program memory.
+
+A VM must provide support for the following meta-values:
+
+* `entry` - a 64-bit address for where the VM should begin executing code.
+
 # General TODO
 
 * Interrupts