write me

elven-wald/src/lib.rs

@@ -3,9 +3,17 @@ extern crate tracing;
 
 use anyhow::{bail, Context, Result};
 use clap::Parser;
-use elven_parser::defs::Elf;
+use elven_parser::{
+    consts::{self as c, ShType, SHT_PROGBITS},
+    read::{ElfIdent, ElfReader, Offset},
+    write::{self, ElfWriter, Entry, Section},
+};
 use memmap2::Mmap;
-use std::{fs::File, path::PathBuf};
+use std::{
+    fs,
+    io::{BufWriter, Write},
+    path::PathBuf,
+};
 
 #[derive(Debug, Clone, Parser)]
 pub struct Opts {
@@ -17,7 +25,8 @@ pub fn run(opts: Opts) -> Result<()> {
         .objs
         .iter()
         .map(|path| {
-            let file = File::open(path).with_context(|| format!("opening {}", path.display()))?;
+            let file =
+                fs::File::open(path).with_context(|| format!("opening {}", path.display()))?;
             unsafe {
                 Mmap::map(&file).with_context(|| format!("memory mapping {}", path.display()))
             }
@@ -38,11 +47,73 @@ pub fn run(opts: Opts) -> Result<()> {
         .iter()
         .zip(&opts.objs)
         .map(|(mmap, path)| {
-            Elf::new(mmap).with_context(|| format!("parsing ELF file {}", path.display()))
+            ElfReader::new(mmap).with_context(|| format!("parsing ELF file {}", path.display()))
         })
         .collect::<Result<Vec<_>, anyhow::Error>>()?;
 
-    let main_elf = elfs[0];
+    let elf = elfs[0];
+
+    let text_sh = elf.section_header_by_name(b".text")?;
+    let text_content = elf.section_content(text_sh)?;
+
+    let _start_sym = elf.symbol_by_name(b"_start")?;
+
+    let section = _start_sym.shndx;
+
+    let entry = Entry {
+        section,
+        rel_offset: Offset(_start_sym.value.0),
+    };
+
+    write_output(text_content, entry)?;
+
+    Ok(())
+}
+
+fn write_output(text: &[u8], entry: Entry) -> Result<()> {
+    let ident = ElfIdent {
+        magic: *c::ELFMAG,
+        class: c::Class(c::ELFCLASS64),
+        data: c::Data(c::ELFDATA2LSB),
+        version: 1,
+        osabi: c::OsAbi(c::ELFOSABI_SYSV),
+        abiversion: 0,
+        _pad: [0; 7],
+    };
+
+    let header = write::Header {
+        ident,
+        r#type: c::Type(c::ET_DYN),
+        machine: c::Machine(c::EM_X86_64),
+    };
+
+    let mut write = ElfWriter::new(header);
+
+    let text_name = write.add_sh_string(b".text");
+    write.add_section(Section {
+        name: text_name,
+        r#type: ShType(SHT_PROGBITS),
+        flags: 0,
+        fixed_entsize: None,
+        content: text.to_vec(),
+    });
+
+    write.set_entry(entry);
+
+    let output = write.write().context("writing output file")?;
+
+    let mut output_file = fs::File::create("a.out").context("creating ./a.out")?;
+    BufWriter::new(&mut output_file).write_all(&output)?;
+
+    #[allow(unused_mut)]
+    let mut permissions = output_file.metadata()?.permissions();
+    #[cfg(unix)]
+    {
+        use std::os::unix::fs::PermissionsExt;
+        let mode = permissions.mode();
+        permissions.set_mode(mode | 0o111);
+    };
+    output_file.set_permissions(permissions)?;
 
     Ok(())
 }