Re: [PATCH 09/31] gpu: nova-core: factor out a section_name_eq() function

["Gary Guo" <gary@garyguo.net>]

On Wed Dec 3, 2025 at 5:59 AM GMT, John Hubbard wrote:
> Factor out a chunk of complexity into a new subroutine. This is an
> incremental step in adding ELF32 support to the existing ELF64 section
> support, for handling GPU firmware.
>
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> ---
>  drivers/gpu/nova-core/firmware.rs | 39 +++++++++++++++----------------
>  1 file changed, 19 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/gpu/nova-core/firmware.rs b/drivers/gpu/nova-core/firmware.rs
> index 31a89abc5a87..5ed079a45ec2 100644
> --- a/drivers/gpu/nova-core/firmware.rs
> +++ b/drivers/gpu/nova-core/firmware.rs
> @@ -267,6 +267,24 @@ unsafe impl FromBytes for Elf64Hdr {}
>      // SAFETY: all bit patterns are valid for this type, and it doesn't use interior mutability.
>      unsafe impl FromBytes for Elf64SHdr {}
>  
> +    /// Check if the section name at `strtab_offset + name_offset` equals `target`.
> +    fn section_name_eq(elf: &[u8], strtab_offset: u64, name_offset: u32, target: &str) -> bool {
> +        strtab_offset
> +            // Compute the index into the ELF image.
> +            .checked_add(u64::from(name_offset))
> +            .and_then(|idx| usize::try_from(idx).ok())
> +            // Get the start of the name.
> +            .and_then(|name_idx| elf.get(name_idx..))
> +            // Stop at the first `0`.
> +            .and_then(|s| s.get(0..=s.iter().position(|b| *b == 0)?))
> +            // Convert into CStr.
> +            .and_then(|s| CStr::from_bytes_with_nul(s).ok())
> +            // Convert into str.
> +            .and_then(|s| s.to_str().ok())
> +            // Check that the name matches.
> +            .is_some_and(|s| s == target)
> +    }

What I would do is to provide a helper function to be obtain a NUL-terminated
string from ELF:

fn elf_str(elf: &[u8], offset: u64) -> Option<&str> {
    // Note that you have a more efficient `from_bytes_until_nul`, you don't
    // need to iterate yourself!
    CStr::from_bytes_until_nul(elf.get(usize::try_from(idx)?..)).ok()?.to_str().ok()
}

and then you can do

strtab_offset.checked_add(name_offest.into()).and_then(|idx| elf_str(elf, idx)).is_some_and(|s| s == target)


> +
>      /// Tries to extract section with name `name` from the ELF64 image `elf`, and returns it.
>      pub(super) fn elf64_section<'a, 'b>(elf: &'a [u8], name: &'b str) -> Option<&'a [u8]> {
>          let hdr = &elf
> @@ -298,26 +316,7 @@ pub(super) fn elf64_section<'a, 'b>(elf: &'a [u8], name: &'b str) -> Option<&'a
>                  return false;
>              };
>  
> -            let Some(name_idx) = strhdr
> -                .0
> -                .sh_offset
> -                .checked_add(u64::from(hdr.0.sh_name))

I think the change is making the code hide the error when ELF is malformed. The
old code fails early which is arguably better?

Best,
Gary

> -                .and_then(|idx| usize::try_from(idx).ok())
> -            else {
> -                return false;
> -            };
> -
> -            // Get the start of the name.
> -            elf.get(name_idx..)
> -                // Stop at the first `0`.
> -                .and_then(|nstr| nstr.get(0..=nstr.iter().position(|b| *b == 0)?))
> -                // Convert into CStr. This should never fail because of the line above.
> -                .and_then(|nstr| CStr::from_bytes_with_nul(nstr).ok())
> -                // Convert into str.
> -                .and_then(|c_str| c_str.to_str().ok())
> -                // Check that the name matches.
> -                .map(|str| str == name)
> -                .unwrap_or(false)
> +            section_name_eq(elf, strhdr.0.sh_offset, hdr.0.sh_name, name)
>          })
>          // Return the slice containing the section.
>          .and_then(|sh| {