[PATCH v9 09/31] gpu: nova-core: don't assume 64-bit firmware images

[John Hubbard]

Introduce a single ELF format abstraction that ties each ELF header
type to its matching section-header type. This keeps the shared
section parser ready for upcoming ELF32 support and avoids mixing
32-bit and 64-bit ELF layouts by mistake.

Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx>
---
 drivers/gpu/nova-core/firmware.rs | 111 ++++++++++++++++++++++--------
 1 file changed, 84 insertions(+), 27 deletions(-)

diff --git a/drivers/gpu/nova-core/firmware.rs b/drivers/gpu/nova-core/firmware.rs
index 6c2ab69cb605..46c26d749a65 100644
--- a/drivers/gpu/nova-core/firmware.rs
+++ b/drivers/gpu/nova-core/firmware.rs
@@ -473,17 +473,72 @@ mod elf {
         transmute::FromBytes, //
     };
 
+    /// Trait to abstract over ELF header differences.
+    trait ElfHeader: FromBytes {
+        fn shnum(&self) -> u16;
+        fn shoff(&self) -> u64;
+        fn shstrndx(&self) -> u16;
+    }
+
+    /// Trait to abstract over ELF section-header differences.
+    trait ElfSectionHeader: FromBytes {
+        fn name(&self) -> u32;
+        fn offset(&self) -> u64;
+        fn size(&self) -> u64;
+    }
+
+    /// Trait describing a matching ELF header and section-header format.
+    trait ElfFormat {
+        type Header: ElfHeader;
+        type SectionHeader: ElfSectionHeader;
+    }
+
     /// Newtype to provide a [`FromBytes`] implementation.
     #[repr(transparent)]
     struct Elf64Hdr(bindings::elf64_hdr);
     // SAFETY: all bit patterns are valid for this type, and it doesn't use interior mutability.
     unsafe impl FromBytes for Elf64Hdr {}
 
+    impl ElfHeader for Elf64Hdr {
+        fn shnum(&self) -> u16 {
+            self.0.e_shnum
+        }
+
+        fn shoff(&self) -> u64 {
+            self.0.e_shoff
+        }
+
+        fn shstrndx(&self) -> u16 {
+            self.0.e_shstrndx
+        }
+    }
+
     #[repr(transparent)]
     struct Elf64SHdr(bindings::elf64_shdr);
     // SAFETY: all bit patterns are valid for this type, and it doesn't use interior mutability.
     unsafe impl FromBytes for Elf64SHdr {}
 
+    impl ElfSectionHeader for Elf64SHdr {
+        fn name(&self) -> u32 {
+            self.0.sh_name
+        }
+
+        fn offset(&self) -> u64 {
+            self.0.sh_offset
+        }
+
+        fn size(&self) -> u64 {
+            self.0.sh_size
+        }
+    }
+
+    struct Elf64Format;
+
+    impl ElfFormat for Elf64Format {
+        type Header = Elf64Hdr;
+        type SectionHeader = Elf64SHdr;
+    }
+
     /// Returns a NULL-terminated string from the ELF image at `offset`.
     fn elf_str(elf: &[u8], offset: u64) -> Option<&str> {
         let idx = usize::try_from(offset).ok()?;
@@ -491,47 +546,49 @@ fn elf_str(elf: &[u8], offset: u64) -> Option<&str> {
         CStr::from_bytes_until_nul(bytes).ok()?.to_str().ok()
     }
 
-    /// 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
-            .get(0..size_of::<bindings::elf64_hdr>())
-            .and_then(Elf64Hdr::from_bytes)?
-            .0;
-
-        // Get all the section headers.
-        let mut shdr = {
-            let shdr_num = usize::from(hdr.e_shnum);
-            let shdr_start = usize::try_from(hdr.e_shoff).ok()?;
-            let shdr_end = shdr_num
-                .checked_mul(size_of::<Elf64SHdr>())
-                .and_then(|v| v.checked_add(shdr_start))?;
-
-            elf.get(shdr_start..shdr_end)
-                .map(|slice| slice.chunks_exact(size_of::<Elf64SHdr>()))?
-        };
+    fn elf_section_generic<'a, F>(elf: &'a [u8], name: &str) -> Option<&'a [u8]>
+    where
+        F: ElfFormat,
+    {
+        let hdr = F::Header::from_bytes(elf.get(0..size_of::<F::Header>())?)?;
+
+        let shdr_num = usize::from(hdr.shnum());
+        let shdr_start = usize::try_from(hdr.shoff()).ok()?;
+        let shdr_end = shdr_num
+            .checked_mul(size_of::<F::SectionHeader>())
+            .and_then(|v| v.checked_add(shdr_start))?;
+
+        // Get all the section headers as an iterator over byte chunks.
+        let shdr_bytes = elf.get(shdr_start..shdr_end)?;
+        let mut shdr_iter = shdr_bytes.chunks_exact(size_of::<F::SectionHeader>());
 
         // Get the strings table.
-        let strhdr = shdr
+        let strhdr = shdr_iter
             .clone()
-            .nth(usize::from(hdr.e_shstrndx))
-            .and_then(Elf64SHdr::from_bytes)?;
+            .nth(usize::from(hdr.shstrndx()))
+            .and_then(F::SectionHeader::from_bytes)?;
 
         // Find the section which name matches `name` and return it.
-        shdr.find_map(|sh| {
-            let hdr = Elf64SHdr::from_bytes(sh)?;
-            let name_offset = strhdr.0.sh_offset.checked_add(u64::from(hdr.0.sh_name))?;
+        shdr_iter.find_map(|sh_bytes| {
+            let sh = F::SectionHeader::from_bytes(sh_bytes)?;
+            let name_offset = strhdr.offset().checked_add(u64::from(sh.name()))?;
             let section_name = elf_str(elf, name_offset)?;
 
             if section_name != name {
                 return None;
             }
 
-            let start = usize::try_from(hdr.0.sh_offset).ok()?;
-            let end = usize::try_from(hdr.0.sh_size)
+            let start = usize::try_from(sh.offset()).ok()?;
+            let end = usize::try_from(sh.size())
                 .ok()
-                .and_then(|sh_size| start.checked_add(sh_size))?;
+                .and_then(|sz| start.checked_add(sz))?;
 
             elf.get(start..end)
         })
     }
+
+    /// Tries to extract section with name `name` from the ELF64 image `elf`, and returns it.
+    pub(super) fn elf64_section<'a>(elf: &'a [u8], name: &str) -> Option<&'a [u8]> {
+        elf_section_generic::<Elf64Format>(elf, name)
+    }
 }
-- 
2.53.0