elf.parse: added lazy_parse function

src/elf/mod.rs

@@ -202,9 +202,56 @@ if_sylvan! {
         pub fn is_object_file(&self) -> bool {
             self.header.e_type == header::ET_REL
         }
+
+        pub fn parse_elf_hdr(bytes: &'a [u8]) -> error::Result<Header> {
+            bytes.pread::<Header>(0)
+        }
+
+        // Lazy parse the ELF contents after parsing headers, program headers and interpreter. This function mainly just assembles
+        // an Elf struct. Once we have the struct, we can choose to parse whatever we want.
+        pub fn lazy_parse(header: Header, program_headers: ProgramHeaders, interpreter: Option<&'a str>) -> error::Result<Self> {
+            let entry = header.e_entry as usize;
+            let is_lib = header.e_type == header::ET_DYN;
+            let is_lsb = header.e_ident[header::EI_DATA] == header::ELFDATA2LSB;
+            let endianness = scroll::Endian::from(is_lsb);
+            let class = header.e_ident[header::EI_CLASS];
+            if class != header::ELFCLASS64 && class != header::ELFCLASS32 {
+                return Err(error::Error::Malformed(format!("Unknown values in ELF ident header: class: {} endianness: {}",
+                                                           class,
+                                                           header.e_ident[header::EI_DATA])));
+            }
+            let is_64 = class == header::ELFCLASS64;
+            let container = if is_64 { Container::Big } else { Container::Little };
+            let ctx = Ctx::new(container, endianness);
+
+            Ok(Elf {
+                header,
+                program_headers,
+                section_headers: Default::default(),
+                shdr_strtab: Default::default(),
+                dynamic: None,
+                dynsyms: Default::default(),
+                dynstrtab: Strtab::default(),
+                syms: Default::default(),
+                strtab: Default::default(),
+                dynrelas: Default::default(),
+                dynrels: Default::default(),
+                pltrelocs: Default::default(),
+                shdr_relocs: Default::default(),
+                soname: None,
+                interpreter,
+                libraries: vec![],
+                is_64,
+                is_lib,
+                entry: entry as u64,
+                little_endian: is_lsb,
+                ctx,
+            })
+        }
+
         /// Parses the contents of the byte stream in `bytes`, and maybe returns a unified binary
         pub fn parse(bytes: &'a [u8]) -> error::Result<Self> {
-            let header = bytes.pread::<Header>(0)?;
+            let header = Self::parse_elf_hdr(bytes)?;
             let entry = header.e_entry as usize;
             let is_lib = header.e_type == header::ET_DYN;
             let is_lsb = header.e_ident[header::EI_DATA] == header::ELFDATA2LSB;