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- "use strict";
- // A minimal elf parser for loading 32 bit, x86, little endian, executable elf files
- const ELF_MAGIC = 0x464C457F;
- let types = DataView.prototype;
- let U8 = { size: 1, get: types.getUint8, set: types.setUint8, };
- let U16 = { size: 2, get: types.getUint16, set: types.setUint16, };
- let U32 = { size: 4, get: types.getUint32, set: types.setUint32, };
- let pad = function(size)
- {
- return {
- size,
- get: offset => -1,
- };
- };
- let Header = create_struct([
- { magic: U32, },
- { class: U8, },
- { data: U8, },
- { version0: U8, },
- { osabi: U8, },
- { abiversion: U8, },
- { pad0: pad(7) },
- { type: U16, },
- { machine: U16, },
- { version1: U32, },
- { entry: U32, },
- { phoff: U32, },
- { shoff: U32, },
- { flags: U32, },
- { ehsize: U16, },
- { phentsize: U16, },
- { phnum: U16, },
- { shentsize: U16, },
- { shnum: U16, },
- { shstrndx: U16, },
- ]);
- console.assert(Header.reduce((a, entry) => a + entry.size, 0) === 52);
- let ProgramHeader = create_struct([
- { type: U32, },
- { offset: U32, },
- { vaddr: U32, },
- { paddr: U32, },
- { filesz: U32, },
- { memsz: U32, },
- { flags: U32, },
- { align: U32, },
- ]);
- console.assert(ProgramHeader.reduce((a, entry) => a + entry.size, 0) === 32);
- let SectionHeader = create_struct([
- { name: U32, },
- { type: U32, },
- { flags: U32, },
- { addr: U32, },
- { offset: U32, },
- { size: U32, },
- { link: U32, },
- { info: U32, },
- { addralign: U32, },
- { entsize: U32, },
- ]);
- console.assert(SectionHeader.reduce((a, entry) => a + entry.size, 0) === 40);
- // From [{ name: type }, ...] to [{ name, type, size, get, set }, ...]
- function create_struct(struct)
- {
- return struct.map(function(entry)
- {
- let keys = Object.keys(entry);
- console.assert(keys.length === 1);
- let name = keys[0];
- let type = entry[name];
- console.assert(type.size > 0);
- return {
- name,
- type,
- size: type.size,
- get: type.get,
- set: type.set,
- };
- });
- }
- /** @param {ArrayBuffer} buffer */
- function read_elf(buffer)
- {
- let view = new DataView(buffer);
- let [header, offset] = read_struct(view, Header);
- console.assert(offset === 52);
- if(DEBUG)
- {
- for(let key of Object.keys(header))
- {
- dbg_log(key + ": 0x" + (header[key].toString(16) >>> 0));
- }
- }
- console.assert(header.magic === ELF_MAGIC, "Bad magic");
- console.assert(header.class === 1, "Unimplemented: 64 bit elf");
- console.assert(header.data === 1, "Unimplemented: big endian");
- console.assert(header.version0 === 1, "Bad version0");
- // 1, 2, 3, 4 specify whether the object is relocatable, executable,
- // shared, or core, respectively.
- console.assert(header.type === 2, "Unimplemented type");
- console.assert(header.version1 === 1, "Bad version1");
- // these are different in 64 bit
- console.assert(header.ehsize === 52, "Bad header size");
- console.assert(header.phentsize === 32, "Bad program header size");
- console.assert(header.shentsize === 40, "Bad section header size");
- let [program_headers, ph_offset] = read_structs(
- view_slice(view, header.phoff, header.phentsize * header.phnum),
- ProgramHeader,
- header.phnum);
- let [sections_headers, sh_offset] = read_structs(
- view_slice(view, header.shoff, header.shentsize * header.shnum),
- SectionHeader,
- header.shnum);
- if(DEBUG && LOG_LEVEL)
- {
- console.log("%d program headers:", program_headers.length);
- for(let program of program_headers)
- {
- console.log(
- "type=%s offset=%s vaddr=%s paddr=%s " +
- "filesz=%s memsz=%s flags=%s align=%s",
- program.type.toString(16),
- program.offset.toString(16),
- program.vaddr.toString(16),
- program.paddr.toString(16),
- program.filesz.toString(16),
- program.memsz.toString(16),
- program.flags.toString(16),
- program.align.toString(16)
- );
- }
- console.log("%d section headers:", sections_headers.length);
- for(let section of sections_headers)
- {
- console.log(
- "name=%s type=%s flags=%s addr=%s offset=%s " +
- "size=%s link=%s info=%s addralign=%s entsize=%s",
- section.name.toString(16),
- section.type.toString(16),
- section.flags.toString(16),
- section.addr.toString(16),
- section.offset.toString(16),
- section.size.toString(16),
- section.link.toString(16),
- section.info.toString(16),
- section.addralign.toString(16),
- section.entsize.toString(16)
- );
- }
- }
- return {
- header,
- program_headers,
- sections_headers,
- };
- }
- function read_struct(view, Struct)
- {
- let result = {};
- let offset = 0;
- const LITTLE_ENDIAN = true; // big endian not supported yet
- for(let entry of Struct)
- {
- let value = entry.get.call(view, offset, LITTLE_ENDIAN);
- console.assert(result[entry.name] === undefined);
- result[entry.name] = value;
- offset += entry.size;
- }
- return [result, offset];
- }
- function read_structs(view, Struct, count)
- {
- let result = [];
- let offset = 0;
- for(var i = 0; i < count; i++)
- {
- let [s, size] = read_struct(view_slice(view, offset), Struct);
- result.push(s);
- offset += size;
- }
- return [result, offset];
- }
- /** @param {number=} length */
- function view_slice(view, offset, length)
- {
- return new DataView(view.buffer, view.byteOffset + offset, length);
- }
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