read/macho: fix data for segments in dyld caches

This is for operations on the segment itself, and for section relocations.
Individual section data was already using the correct source.

src/read/macho/file.rs

@@ -44,7 +44,7 @@ where
     pub(super) header_offset: u64,
     pub(super) header: &'data Mach,
     pub(super) segments: Vec<MachOSegmentInternal<'data, Mach, R>>,
-    pub(super) sections: Vec<MachOSectionInternal<'data, Mach>>,
+    pub(super) sections: Vec<MachOSectionInternal<'data, Mach, R>>,
     pub(super) symbols: SymbolTable<'data, Mach, R>,
 }
 
@@ -65,11 +65,10 @@ where
         if let Ok(mut commands) = header.load_commands(endian, data, 0) {
             while let Ok(Some(command)) = commands.next() {
                 if let Some((segment, section_data)) = Mach::Segment::from_command(command)? {
-                    let segment_index = segments.len();
                     segments.push(MachOSegmentInternal { segment, data });
                     for section in segment.sections(endian, section_data)? {
                         let index = SectionIndex(sections.len() + 1);
-                        sections.push(MachOSectionInternal::parse(index, segment_index, section));
+                        sections.push(MachOSectionInternal::parse(index, section, data));
                     }
                 } else if let Some(symtab) = command.symtab()? {
                     symbols = symtab.symbols(endian, data)?;
@@ -110,6 +109,7 @@ where
                 if let Some((segment, section_data)) = Mach::Segment::from_command(command)? {
                     // Each segment can be stored in a different subcache. Get the segment's
                     // address and look it up in the cache mappings, to find the correct cache data.
+                    // This was observed for the arm64e __LINKEDIT segment in macOS 12.0.1.
                     let addr = segment.vmaddr(endian).into();
                     let (data, _offset) = image
                         .cache
@@ -118,12 +118,11 @@ where
                     if segment.name() == macho::SEG_LINKEDIT.as_bytes() {
                         linkedit_data = Some(data);
                     }
-                    let segment_index = segments.len();
                     segments.push(MachOSegmentInternal { segment, data });
 
                     for section in segment.sections(endian, section_data)? {
                         let index = SectionIndex(sections.len() + 1);
-                        sections.push(MachOSectionInternal::parse(index, segment_index, section));
+                        sections.push(MachOSectionInternal::parse(index, section, data));
                     }
                 } else if let Some(st) = command.symtab()? {
                     symtab = Some(st);
@@ -154,23 +153,14 @@ where
     pub(super) fn section_internal(
         &self,
         index: SectionIndex,
-    ) -> Result<&MachOSectionInternal<'data, Mach>> {
+    ) -> Result<&MachOSectionInternal<'data, Mach, R>> {
         index
             .0
             .checked_sub(1)
             .and_then(|index| self.sections.get(index))
             .read_error("Invalid Mach-O section index")
     }
 
-    pub(super) fn segment_internal(
-        &self,
-        index: usize,
-    ) -> Result<&MachOSegmentInternal<'data, Mach, R>> {
-        self.segments
-            .get(index)
-            .read_error("Invalid Mach-O segment index")
-    }
-
     /// Returns the endianness.
     pub fn endian(&self) -> Mach::Endian {
         self.endian

src/read/macho/section.rs

@@ -25,7 +25,7 @@ where
     R: ReadRef<'data>,
 {
     pub(super) file: &'file MachOFile<'data, Mach, R>,
-    pub(super) iter: slice::Iter<'file, MachOSectionInternal<'data, Mach>>,
+    pub(super) iter: slice::Iter<'file, MachOSectionInternal<'data, Mach, R>>,
 }
 
 impl<'data, 'file, Mach, R> fmt::Debug for MachOSectionIterator<'data, 'file, Mach, R>
@@ -71,7 +71,7 @@ where
     R: ReadRef<'data>,
 {
     pub(super) file: &'file MachOFile<'data, Mach, R>,
-    pub(super) internal: MachOSectionInternal<'data, Mach>,
+    pub(super) internal: MachOSectionInternal<'data, Mach, R>,
 }
 
 impl<'data, 'file, Mach, R> MachOSection<'data, 'file, Mach, R>
@@ -80,11 +80,9 @@ where
     R: ReadRef<'data>,
 {
     fn bytes(&self) -> Result<&'data [u8]> {
-        let segment_index = self.internal.segment_index;
-        let segment = self.file.segment_internal(segment_index)?;
         self.internal
             .section
-            .data(self.file.endian, segment.data)
+            .data(self.file.endian, self.internal.data)
             .read_error("Invalid Mach-O section size or offset")
     }
 }
@@ -193,7 +191,7 @@ where
             relocations: self
                 .internal
                 .section
-                .relocations(self.file.endian, self.file.data)
+                .relocations(self.file.endian, self.internal.data)
                 .unwrap_or(&[])
                 .iter(),
         }
@@ -211,19 +209,19 @@ where
 }
 
 #[derive(Debug, Clone, Copy)]
-pub(super) struct MachOSectionInternal<'data, Mach: MachHeader> {
+pub(super) struct MachOSectionInternal<'data, Mach: MachHeader, R: ReadRef<'data>> {
     pub index: SectionIndex,
-    pub segment_index: usize,
     pub kind: SectionKind,
     pub section: &'data Mach::Section,
+    /// The data for the file that contains the section data.
+    ///
+    /// This is required for dyld caches, where this may be a different subcache
+    /// from the file containing the Mach-O load commands.
+    pub data: R,
 }
 
-impl<'data, Mach: MachHeader> MachOSectionInternal<'data, Mach> {
-    pub(super) fn parse(
-        index: SectionIndex,
-        segment_index: usize,
-        section: &'data Mach::Section,
-    ) -> Self {
+impl<'data, Mach: MachHeader, R: ReadRef<'data>> MachOSectionInternal<'data, Mach, R> {
+    pub(super) fn parse(index: SectionIndex, section: &'data Mach::Section, data: R) -> Self {
         // TODO: we don't validate flags, should we?
         let kind = match (section.segment_name(), section.name()) {
             (b"__TEXT", b"__text") => SectionKind::Text,
@@ -246,9 +244,9 @@ impl<'data, Mach: MachHeader> MachOSectionInternal<'data, Mach> {
         };
         MachOSectionInternal {
             index,
-            segment_index,
             kind,
             section,
+            data,
         }
     }
 }

src/read/macho/segment.rs

@@ -69,7 +69,7 @@ where
     fn bytes(&self) -> Result<&'data [u8]> {
         self.internal
             .segment
-            .data(self.file.endian, self.file.data)
+            .data(self.file.endian, self.internal.data)
             .read_error("Invalid Mach-O segment size or offset")
     }
 }
@@ -149,8 +149,12 @@ where
 
 #[derive(Debug, Clone, Copy)]
 pub(super) struct MachOSegmentInternal<'data, Mach: MachHeader, R: ReadRef<'data>> {
-    pub data: R,
     pub segment: &'data Mach::Segment,
+    /// The data for the file that contains the segment data.
+    ///
+    /// This is required for dyld caches, where this may be a different subcache
+    /// from the file containing the Mach-O load commands.
+    pub data: R,
 }
 
 /// A trait for generic access to [`macho::SegmentCommand32`] and [`macho::SegmentCommand64`].