Introduce ElfN_Nhdr type

The Elf32_Nhdr and Elf64_Nhdr types have the same size and layout. So
far we have not exploited this fact and just stuck to the existing logic
of differentiating between 32 and 64 bit types depending on the ELF
bitness, as we do elsewhere.
However, there is a certain amount of complexity associated with
supporting the two bitnesses. With this change we introduce the
ElfN_Nhdr type as an alias to Elf64_Nhdr and rely solely on it.

Signed-off-by: Daniel Müller <deso@posteo.net>

Author: d-e-s-o

src/elf/types.rs

@@ -1,4 +1,5 @@
 use std::borrow::Cow;
+use std::mem::size_of;
 
 use crate::util::Either;
 use crate::util::Pod;
@@ -613,6 +614,10 @@ impl Has32BitTy for Elf64_Nhdr {
     type Ty32Bit = Elf32_Nhdr;
 }
 
+const _: () = assert!(size_of::<Elf32_Nhdr>() == size_of::<Elf64_Nhdr>());
+
+pub(crate) type ElfN_Nhdr = Elf64_Nhdr;
+
 
 #[derive(Clone, Debug)]
 #[repr(C)]

src/normalize/buildid.rs

@@ -2,8 +2,7 @@ use std::borrow::Cow;
 use std::path::Path;
 
 use crate::elf;
-use crate::elf::types::Elf32_Nhdr;
-use crate::elf::types::Elf64_Nhdr;
+use crate::elf::types::ElfN_Nhdr;
 use crate::elf::ElfParser;
 use crate::file_cache::FileCache;
 use crate::log::warn;
@@ -27,14 +26,9 @@ fn read_build_id_from_notes(parser: &ElfParser) -> Result<Option<BuildId<'_>>> {
             // SANITY: We just found the index so the section data should always
             //         be found.
             let mut bytes = parser.section_data(idx).unwrap();
-            let (n_type, n_namesz, n_descsz) = if shdr.is_32bit() {
+            let (n_type, n_namesz, n_descsz) = {
                 let nhdr = bytes
-                    .read_pod_ref::<Elf32_Nhdr>()
-                    .ok_or_invalid_data(|| "failed to read build ID section header")?;
-                (nhdr.n_type, nhdr.n_namesz, nhdr.n_descsz)
-            } else {
-                let nhdr = bytes
-                    .read_pod_ref::<Elf64_Nhdr>()
+                    .read_pod_ref::<ElfN_Nhdr>()
                     .ok_or_invalid_data(|| "failed to read build ID section header")?;
                 (nhdr.n_type, nhdr.n_namesz, nhdr.n_descsz)
             };
@@ -75,14 +69,9 @@ fn read_build_id_from_section_name(parser: &ElfParser) -> Result<Option<BuildId<
         // SANITY: We just found the index so the section should always be
         //         found.
         let mut bytes = parser.section_data(idx).unwrap();
-        let (n_namesz, n_descsz) = if shdr.is_32bit() {
-            let nhdr = bytes
-                .read_pod_ref::<Elf32_Nhdr>()
-                .ok_or_invalid_data(|| "failed to read build ID section header")?;
-            (nhdr.n_namesz, nhdr.n_descsz)
-        } else {
+        let (n_namesz, n_descsz) = {
             let nhdr = bytes
-                .read_pod_ref::<Elf64_Nhdr>()
+                .read_pod_ref::<ElfN_Nhdr>()
                 .ok_or_invalid_data(|| "failed to read build ID section header")?;
             (nhdr.n_namesz, nhdr.n_descsz)
         };