elf: gnu symbol versioning (#280)

* elf.dynamic: Parse DT_VERDEF + DT_VERDEFNUM dynamic tags into DynamicInfo struct
* elf.symver: add struct definitions and reading part for .gnu.version_r (SHT_GNU_verdef) section
* elf.symver: add tests for parsing .gnu.version_r section
* elf.symver: make structs used by user more ergonomic by using usize

Implement some std traits:
    - IntoIter
    - ExactSizeIterator
    - FusedIterator

* elf.symver: add struct definitions and reading part for .gnu.version_d (SHT_GNU_verdef) section + doc example
* elf.symver: Use sub-module as feature guard

Use sub-module rather than macro to implement feature guard, as
`cargo fmt` doesn't seem to see through the macro based approach.

* add tests for parsing .gnu.version_d section
* elf.symver: add struct definitions and reading part for .gnu.version (SHT_GNU_versym) section
* elf.symver: add tests for parsing .gnu.version section
* elf.symver: added some convenience methods to Verdef
- Return 0 as lower bound in size_hint impls (better hint for corrupt
  ELFs)
- Verdef/Verdaux/Verneed/Vernaux Iterator: Start yielding None on the
  next call if there is no valid next index

src/elf/dynamic.rs

@@ -614,6 +614,8 @@ macro_rules! elf_dynamic_info_std_impl {
             pub pltrelsz: usize,
             pub pltrel: $size,
             pub jmprel: usize,
+            pub verdef: $size,
+            pub verdefnum: $size,
             pub verneed: $size,
             pub verneednum: $size,
             pub versym: $size,
@@ -658,6 +660,8 @@ macro_rules! elf_dynamic_info_std_impl {
                     DT_JMPREL => {
                         self.jmprel = vm_to_offset(phdrs, dynamic.d_val).unwrap_or(0) as usize
                     } // .rela.plt
+                    DT_VERDEF => self.verdef = vm_to_offset(phdrs, dynamic.d_val).unwrap_or(0),
+                    DT_VERDEFNUM => self.verdefnum = vm_to_offset(phdrs, dynamic.d_val).unwrap_or(0),
                     DT_VERNEED => self.verneed = vm_to_offset(phdrs, dynamic.d_val).unwrap_or(0),
                     DT_VERNEEDNUM => self.verneednum = dynamic.d_val as _,
                     DT_VERSYM => self.versym = vm_to_offset(phdrs, dynamic.d_val).unwrap_or(0),
@@ -750,6 +754,8 @@ macro_rules! elf_dynamic_info_std_impl {
                         .field("pltrelsz", &self.pltrelsz)
                         .field("pltrel", &self.pltrel)
                         .field("jmprel", &format_args!("0x{:x}", self.jmprel))
+                        .field("verdef", &format_args!("0x{:x}", self.verdef))
+                        .field("verdefnum", &self.verdefnum)
                         .field("verneed", &format_args!("0x{:x}", self.verneed))
                         .field("verneednum", &self.verneednum)
                         .field("versym", &format_args!("0x{:x}", self.versym))

src/elf/mod.rs

@@ -53,6 +53,8 @@ pub mod dynamic;
 #[macro_use]
 pub mod reloc;
 pub mod note;
+#[cfg(all(any(feature = "elf32", feature = "elf64"), feature = "alloc"))]
+pub mod symver;
 
 macro_rules! if_sylvan {
     ($($i:item)*) => ($(
@@ -78,6 +80,7 @@ if_sylvan! {
     pub use dynamic::Dynamic;
     pub use reloc::Reloc;
     pub use reloc::RelocSection;
+    pub use symver::{VersymSection, VerdefSection, VerneedSection};
 
     pub type ProgramHeaders = Vec<ProgramHeader>;
     pub type SectionHeaders = Vec<SectionHeader>;
@@ -130,6 +133,15 @@ if_sylvan! {
         pub entry: u64,
         /// Whether the binary is little endian or not
         pub little_endian: bool,
+        /// Contains the symbol version information from the optional section
+        /// [`SHT_GNU_VERSYM`][section_header::SHT_GNU_VERSYM] (GNU extenstion).
+        pub versym : Option<VersymSection<'a>>,
+        /// Contains the version definition information from the optional section
+        /// [`SHT_GNU_VERDEF`][section_header::SHT_GNU_VERDEF] (GNU extenstion).
+        pub verdef : Option<VerdefSection<'a>>,
+        /// Contains the version needed information from the optional section
+        /// [`SHT_GNU_VERNEED`][section_header::SHT_GNU_VERNEED] (GNU extenstion).
+        pub verneed : Option<VerneedSection<'a>>,
         ctx: Ctx,
     }
 
@@ -232,6 +244,9 @@ if_sylvan! {
                 entry: misc.entry,
                 little_endian: misc.little_endian,
                 ctx: misc.ctx,
+                versym: None,
+                verdef: None,
+                verneed: None,
             })
         }
 
@@ -334,6 +349,10 @@ if_sylvan! {
                 }
             }
 
+            let versym = symver::VersymSection::parse(bytes, &section_headers, ctx)?;
+            let verdef = symver::VerdefSection::parse(bytes, &section_headers, ctx)?;
+            let verneed = symver::VerneedSection::parse(bytes, &section_headers, ctx)?;
+
             Ok(Elf {
                 header,
                 program_headers,
@@ -356,6 +375,9 @@ if_sylvan! {
                 entry: misc.entry,
                 little_endian: misc.little_endian,
                 ctx: ctx,
+                versym,
+                verdef,
+                verneed,
             })
         }
     }