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Only lookup build ID by section type
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The .note.gnu.build-id name for the section containing the GNU build ID
is not normative -- it may or may not exist, even if a build ID is
present. So far we have used both by-name look up and more extensive
iteration over available note sections. However, that ultimately results
in a bunch of similar looking but effectively duplicate code. Let's
agree on a single approach to discovering the build ID, which is by
iterating over note sections and checking for the corresponding note
type.

Signed-off-by: Daniel Müller <[email protected]>
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@d-e-s-o
d-e-s-o committed Jan 9, 2025
1 parent a477e05 commit 1b994fd
Showing 1 changed file with 7 additions and 66 deletions.
73 changes: 7 additions & 66 deletions src/normalize/buildid.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -6,7 +6,6 @@ use crate::elf;
use crate::elf::types::ElfN_Nhdr;
use crate::elf::ElfParser;
use crate::file_cache::FileCache;
use crate::log::warn;
use crate::util::align_up_u32;
use crate::util::ReadRaw as _;
use crate::Error;
Expand All @@ -21,7 +20,7 @@ pub type BuildId<'src> = Cow<'src, [u8]>;

/// Iterate over all note sections to find one of type
/// [`NT_GNU_BUILD_ID`][elf::types::NT_GNU_BUILD_ID].
fn read_build_id_from_notes(parser: &ElfParser) -> Result<Option<BuildId<'_>>> {
fn read_build_id(parser: &ElfParser) -> Result<Option<BuildId<'_>>> {
let shdrs = parser.section_headers()?;
for (idx, shdr) in shdrs.iter(0).enumerate() {
if shdr.type_() == elf::types::SHT_NOTE {
Expand Down Expand Up @@ -56,61 +55,6 @@ fn read_build_id_from_notes(parser: &ElfParser) -> Result<Option<BuildId<'_>>> {
Ok(None)
}

/// Attempt to read an ELF binary's build ID from the .note.gnu.build-id
/// section.
fn read_build_id_from_section_name(parser: &ElfParser) -> Result<Option<BuildId<'_>>> {
let build_id_section = ".note.gnu.build-id";
// The build ID is contained in the `.note.gnu.build-id` section. See
// elf(5).
if let Ok(Some(idx)) = parser.find_section(build_id_section) {
// SANITY: We just found the index so the section should always be
// found.
let shdr = parser.section_headers()?.get(idx).unwrap();
let sh_type = shdr.type_();

if sh_type != elf::types::SHT_NOTE {
warn!("build ID section {build_id_section} is of unsupported type ({sh_type})");
return Ok(None)
}

// 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) = {
let nhdr = bytes
.read_pod_ref::<ElfN_Nhdr>()
.ok_or_invalid_data(|| "failed to read build ID section header")?;
(nhdr.n_namesz, nhdr.n_descsz)
};

let name = bytes
.read_slice(n_namesz as _)
.and_then(|mut name| name.read_cstr())
.ok_or_invalid_data(|| "failed to read build ID section name")?;
if name.to_bytes() != b"GNU" {
warn!("encountered unsupported build ID type {:?}; ignoring", name);
Ok(None)
} else {
let build_id = bytes
.read_slice(n_descsz as _)
.ok_or_invalid_data(|| "failed to read build ID section contents")?;
Ok(Some(Cow::Borrowed(build_id)))
}
} else {
Ok(None)
}
}


fn read_build_id_impl(parser: &ElfParser) -> Result<Option<BuildId>> {
if let Some(build_id) = read_build_id_from_section_name(parser)? {
Ok(Some(build_id))
} else if let Some(build_id) = read_build_id_from_notes(parser)? {
Ok(Some(build_id))
} else {
Ok(None)
}
}

pub(super) trait BuildIdReader<'src> {
fn read_build_id(&self, path: &Path) -> Option<BuildId<'src>> {
Expand Down Expand Up @@ -138,7 +82,7 @@ impl BuildIdReader<'_> for DefaultBuildIdReader {
/// Attempt to read an ELF binary's build ID from a file.
fn read_build_id_fallible(&self, path: &Path) -> Result<Option<BuildId<'static>>> {
let parser = ElfParser::open(path)?;
let buildid = read_build_id_impl(&parser)?.map(|buildid| Cow::Owned(buildid.to_vec()));
let buildid = read_build_id(&parser)?.map(|buildid| Cow::Owned(buildid.to_vec()));
Ok(buildid)
}
}
Expand All @@ -163,8 +107,7 @@ impl<'src> BuildIdReader<'src> for CachingBuildIdReader<'src> {
let build_id = cell
.get_or_try_init(|| {
let parser = ElfParser::open_file(file, path)?;
let buildid =
read_build_id_impl(&parser)?.map(|buildid| Cow::Owned(buildid.to_vec()));
let buildid = read_build_id(&parser)?.map(|buildid| Cow::Owned(buildid.to_vec()));
Result::<_, Error>::Ok(buildid)
})?
.as_deref()
Expand Down Expand Up @@ -227,7 +170,7 @@ where
P: AsRef<Path> + ?Sized,
{
let parser = ElfParser::open(path.as_ref())?;
let buildid = read_build_id_impl(&parser)?.map(|buildid| Cow::Owned(buildid.to_vec()));
let buildid = read_build_id(&parser)?.map(|buildid| Cow::Owned(buildid.to_vec()));
Ok(buildid)
}

Expand All @@ -240,7 +183,7 @@ where
#[inline]
pub fn read_elf_build_id_from_mmap(mmap: &Mmap) -> Result<Option<BuildId<'static>>> {
let parser = ElfParser::from_mmap(mmap.clone(), None);
let buildid = read_build_id_impl(&parser)?.map(|buildid| Cow::Owned(buildid.to_vec()));
let buildid = read_build_id(&parser)?.map(|buildid| Cow::Owned(buildid.to_vec()));
Ok(buildid)
}

Expand Down Expand Up @@ -271,10 +214,8 @@ mod tests {
assert_eq!(build_id.len(), 20, "'{build_id:?}'");
}

test("libtest-so.so", read_build_id_from_section_name);
test("libtest-so.so", read_build_id_from_notes);
test("libtest-so-32.so", read_build_id_from_section_name);
test("libtest-so-32.so", read_build_id_from_notes);
test("libtest-so.so", read_build_id);
test("libtest-so-32.so", read_build_id);
}

/// Check that we can read a binary's build ID.
Expand Down

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