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write/macho: fix ARM64_RELOC_ADDEND handling
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- fix SectionHeader::nreloc to include additional ARM64_RELOC_ADDEND relocations
- switch order of ARM64_RELOC_ADDEND and its paired relocation
- emit ARM64_RELOC_ADDEND for more relocation types
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@philipc
philipc committed Oct 24, 2023
1 parent 17c4103 commit edd17a5
Showing 1 changed file with 68 additions and 47 deletions.
115 changes: 68 additions & 47 deletions src/write/macho.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,7 @@ struct SectionOffsets {
offset: usize,
address: u64,
reloc_offset: usize,
reloc_count: usize,
}

#[derive(Default, Clone, Copy)]
Expand Down Expand Up @@ -259,7 +260,6 @@ impl<'a> Object<'a> {
| RelocationKind::MachO { relative: true, .. } => true,
_ => false,
};
let mut constant = relocation.addend;
if relative {
// For PC relative relocations on some architectures, the
// addend does not include the offset required due to the
Expand All @@ -286,13 +286,29 @@ impl<'a> Object<'a> {
// TODO: maybe missing support for some architectures and relocations
_ => 0,
};
constant += pcrel_offset;
relocation.addend += pcrel_offset;
}
// Aarch64 relocs of these sizes act as if they are double-word length
if self.architecture == Architecture::Aarch64 && matches!(relocation.size, 12 | 21 | 26) {
relocation.size = 32;
}
relocation.addend -= constant;
// Check for relocations that use an explicit addend.
if self.architecture == Architecture::Aarch64 {
if relocation.encoding == RelocationEncoding::AArch64Call {
return 0;
}
if let RelocationKind::MachO { value, .. } = relocation.kind {
match value {
macho::ARM64_RELOC_BRANCH26
| macho::ARM64_RELOC_PAGE21
| macho::ARM64_RELOC_PAGEOFF12 => return 0,
_ => {}
}
}
}
// Signify implicit addend.
let constant = relocation.addend;
relocation.addend = 0;
constant
}

Expand Down Expand Up @@ -406,10 +422,15 @@ impl<'a> Object<'a> {

// Calculate size of relocations.
for (index, section) in self.sections.iter().enumerate() {
let count = section.relocations.len();
let count: usize = section
.relocations
.iter()
.map(|reloc| 1 + usize::from(reloc.addend != 0))
.sum();
if count != 0 {
offset = align(offset, 4);
section_offsets[index].reloc_offset = offset;
section_offsets[index].reloc_count = count;
let len = count * mem::size_of::<macho::Relocation<Endianness>>();
offset += len;
}
Expand Down Expand Up @@ -547,7 +568,7 @@ impl<'a> Object<'a> {
offset: section_offsets[index].offset as u32,
align: section.align.trailing_zeros(),
reloff: section_offsets[index].reloc_offset as u32,
nreloc: section.relocations.len() as u32,
nreloc: section_offsets[index].reloc_count as u32,
flags,
},
);
Expand Down Expand Up @@ -650,8 +671,38 @@ impl<'a> Object<'a> {
write_align(buffer, 4);
debug_assert_eq!(section_offsets[index].reloc_offset, buffer.len());
for reloc in &section.relocations {
let r_length = match reloc.size {
8 => 0,
16 => 1,
32 => 2,
64 => 3,
_ => return Err(Error(format!("unimplemented reloc size {:?}", reloc))),
};

// Write explicit addend.
if reloc.addend != 0 {
let r_type = match self.architecture {
Architecture::Aarch64 | Architecture::Aarch64_Ilp32 => {
macho::ARM64_RELOC_ADDEND
}
_ => {
return Err(Error(format!("unimplemented relocation {:?}", reloc)))
}
};

let reloc_info = macho::RelocationInfo {
r_address: reloc.offset as u32,
r_symbolnum: reloc.addend as u32,
r_pcrel: false,
r_length,
r_extern: false,
r_type,
};
buffer.write(&reloc_info.relocation(endian));
}

let r_extern;
let mut r_symbolnum;
let r_symbolnum;
let symbol = &self.symbols[reloc.symbol.0];
if symbol.kind == SymbolKind::Section {
r_symbolnum = section_offsets[symbol.section.id().unwrap().0].index as u32;
Expand All @@ -660,82 +711,52 @@ impl<'a> Object<'a> {
r_symbolnum = symbol_offsets[reloc.symbol.0].index as u32;
r_extern = true;
}
let r_length = match reloc.size {
8 => 0,
16 => 1,
32 => 2,
64 => 3,
_ => return Err(Error(format!("unimplemented reloc size {:?}", reloc))),
};
let (r_pcrel, r_type) = match self.architecture {
Architecture::I386 => match reloc.kind {
RelocationKind::Absolute => (false, macho::GENERIC_RELOC_VANILLA),
_ => {
return Err(Error(format!("unimplemented relocation {:?}", reloc)));
}
},
Architecture::X86_64 => match (reloc.kind, reloc.encoding, reloc.addend) {
(RelocationKind::Absolute, RelocationEncoding::Generic, 0) => {
Architecture::X86_64 => match (reloc.kind, reloc.encoding) {
(RelocationKind::Absolute, RelocationEncoding::Generic) => {
(false, macho::X86_64_RELOC_UNSIGNED)
}
(RelocationKind::Relative, RelocationEncoding::Generic, -4) => {
(RelocationKind::Relative, RelocationEncoding::Generic) => {
(true, macho::X86_64_RELOC_SIGNED)
}
(RelocationKind::Relative, RelocationEncoding::X86RipRelative, -4) => {
(RelocationKind::Relative, RelocationEncoding::X86RipRelative) => {
(true, macho::X86_64_RELOC_SIGNED)
}
(RelocationKind::Relative, RelocationEncoding::X86Branch, -4) => {
(RelocationKind::Relative, RelocationEncoding::X86Branch) => {
(true, macho::X86_64_RELOC_BRANCH)
}
(RelocationKind::PltRelative, RelocationEncoding::X86Branch, -4) => {
(RelocationKind::PltRelative, RelocationEncoding::X86Branch) => {
(true, macho::X86_64_RELOC_BRANCH)
}
(RelocationKind::GotRelative, RelocationEncoding::Generic, -4) => {
(RelocationKind::GotRelative, RelocationEncoding::Generic) => {
(true, macho::X86_64_RELOC_GOT)
}
(
RelocationKind::GotRelative,
RelocationEncoding::X86RipRelativeMovq,
-4,
) => (true, macho::X86_64_RELOC_GOT_LOAD),
(RelocationKind::MachO { value, relative }, _, _) => (relative, value),
(RelocationKind::MachO { value, relative }, _) => (relative, value),
_ => {
return Err(Error(format!("unimplemented relocation {:?}", reloc)));
}
},
Architecture::Aarch64 | Architecture::Aarch64_Ilp32 => {
match (reloc.kind, reloc.encoding, reloc.addend) {
(RelocationKind::Absolute, RelocationEncoding::Generic, 0) => {
match (reloc.kind, reloc.encoding) {
(RelocationKind::Absolute, RelocationEncoding::Generic) => {
(false, macho::ARM64_RELOC_UNSIGNED)
}
(RelocationKind::Relative, RelocationEncoding::AArch64Call, 0) => {
(RelocationKind::Relative, RelocationEncoding::AArch64Call) => {
(true, macho::ARM64_RELOC_BRANCH26)
}
// Non-zero addend, so we have to encode the addend separately
(
RelocationKind::Relative,
RelocationEncoding::AArch64Call,
value,
) => {
// first emit the BR26 relocation
let reloc_info = macho::RelocationInfo {
r_address: reloc.offset as u32,
r_symbolnum,
r_pcrel: true,
r_length,
r_extern: true,
r_type: macho::ARM64_RELOC_BRANCH26,
};
buffer.write(&reloc_info.relocation(endian));

// set up a separate relocation for the addend
r_symbolnum = value as u32;
(false, macho::ARM64_RELOC_ADDEND)
}
(
RelocationKind::MachO { value, relative },
RelocationEncoding::Generic,
0,
) => (relative, value),
_ => {
return Err(Error(format!(
Expand Down

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