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Support cross-section relocations #223

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merged 2 commits into from
Nov 15, 2024
Merged

Support cross-section relocations #223

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7ba7528
polkavm-linker: support cross-section relocations
koute Nov 15, 2024
97b3e6b
polkavm-linker: return an error on a 64-bit jump table relocation
koute Nov 15, 2024
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10 changes: 6 additions & 4 deletions crates/polkavm-linker/src/dwarf.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -618,11 +618,13 @@ fn try_fetch_size_relocation(
};

match relocation {
RelocationKind::Size {
section_index,
range,
RelocationKind::Offset {
origin,
target,
size: SizeRelocationSize::Generic(..),
} => Ok(Some((*section_index, *range))),
} if origin.section_index == target.section_index && target.offset >= origin.offset => {
Ok(Some((origin.section_index, (origin.offset..target.offset).into())))
}
RelocationKind::Abs {
target,
size: RelocationSize::U32,
Expand Down
117 changes: 62 additions & 55 deletions crates/polkavm-linker/src/program_from_elf.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -7287,10 +7287,9 @@ pub(crate) enum RelocationKind {
target_code: SectionTarget,
target_base: SectionTarget,
},

Size {
section_index: SectionIndex,
range: AddressRange,
Offset {
origin: SectionTarget,
target: SectionTarget,
size: SizeRelocationSize,
},
}
Expand All @@ -7299,16 +7298,7 @@ impl RelocationKind {
fn targets(&self) -> [Option<SectionTarget>; 2] {
match self {
RelocationKind::Abs { target, .. } => [Some(*target), None],
RelocationKind::Size { section_index, range, .. } => [
Some(SectionTarget {
section_index: *section_index,
offset: range.start,
}),
Some(SectionTarget {
section_index: *section_index,
offset: range.end,
}),
],
RelocationKind::Offset { origin, target, .. } => [Some(*origin), Some(*target)],
RelocationKind::JumpTable { target_code, target_base } => [Some(*target_code), Some(*target_base)],
}
}
Expand Down Expand Up @@ -7448,13 +7438,34 @@ where
continue;
}
[(_, Kind::Mut(MutOp::Add, size_1, target_1)), (_, Kind::Mut(MutOp::Sub, size_2, target_2))]
if size_1 == size_2 && (target_1.section_index == target_2.section_index) =>
if size_1 == size_2
&& matches!(*size_1, RelocationSize::U32 | RelocationSize::U64)
&& code_sections_set.contains(&target_1.section_index)
&& !code_sections_set.contains(&target_2.section_index) =>
{
if *size_1 == RelocationSize::U64 {
// We could support this, but I'm not sure if anything ever emits this,
// so let's return an error for now until somebody complains.
return Err(ProgramFromElfError::other(
"internal error: found 64-bit jump table relocation; please report this",
));
}

relocations.insert(
current_location,
RelocationKind::Size {
section_index: target_1.section_index,
range: (target_2.offset..target_1.offset).into(),
RelocationKind::JumpTable {
target_code: *target_1,
target_base: *target_2,
},
);
continue;
}
[(_, Kind::Mut(MutOp::Add, size_1, target_1)), (_, Kind::Mut(MutOp::Sub, size_2, target_2))] if size_1 == size_2 => {
relocations.insert(
current_location,
RelocationKind::Offset {
origin: *target_2,
target: *target_1,
size: SizeRelocationSize::Generic(*size_1),
},
);
Expand All @@ -7467,59 +7478,40 @@ where
size: size_1,
}),
), (_, Kind::Mut(MutOp::Sub, size_2, target_2))]
if size_1 == size_2 && target_1.section_index == target_2.section_index && target_1.offset >= target_2.offset =>
if size_1 == size_2 =>
{
relocations.insert(
current_location,
RelocationKind::Size {
section_index: target_1.section_index,
range: (target_2.offset..target_1.offset).into(),
RelocationKind::Offset {
origin: *target_2,
target: *target_1,
size: SizeRelocationSize::Generic(*size_1),
},
);
continue;
}
[(_, Kind::Set6 { target: target_1 }), (_, Kind::Sub6 { target: target_2 })]
if target_1.section_index == target_2.section_index && target_1.offset >= target_2.offset =>
{
[(_, Kind::Set6 { target: target_1 }), (_, Kind::Sub6 { target: target_2 })] => {
relocations.insert(
current_location,
RelocationKind::Size {
section_index: target_1.section_index,
range: (target_2.offset..target_1.offset).into(),
RelocationKind::Offset {
origin: *target_2,
target: *target_1,
size: SizeRelocationSize::SixBits,
},
);
continue;
}
[(_, Kind::SetUleb128 { target: target_1 }), (_, Kind::SubUleb128 { target: target_2 })]
if target_1.section_index == target_2.section_index && target_1.offset >= target_2.offset =>
{
[(_, Kind::SetUleb128 { target: target_1 }), (_, Kind::SubUleb128 { target: target_2 })] => {
relocations.insert(
current_location,
RelocationKind::Size {
section_index: target_1.section_index,
range: (target_2.offset..target_1.offset).into(),
RelocationKind::Offset {
origin: *target_2,
target: *target_1,
size: SizeRelocationSize::Uleb128,
},
);
continue;
}
[(_, Kind::Mut(MutOp::Add, size_1, target_1)), (_, Kind::Mut(MutOp::Sub, size_2, target_2))]
if size_1 == size_2
&& *size_1 == RelocationSize::U32
&& code_sections_set.contains(&target_1.section_index)
&& !code_sections_set.contains(&target_2.section_index) =>
{
relocations.insert(
current_location,
RelocationKind::JumpTable {
target_code: *target_1,
target_base: *target_2,
},
);
continue;
}
_ => ErrorToken,
};

Expand Down Expand Up @@ -8750,19 +8742,34 @@ where
}

match relocation {
RelocationKind::Size {
section_index: _,
range,
size,
} => {
// These relocations should only be used in debug info sections.
RelocationKind::Offset { origin, target, size } => {
// These relocations should only be used in debug info sections and RO data sections.
if reachability_graph.is_data_section_reachable(section.index()) && !matches!(size, SizeRelocationSize::Generic(..)) {
return Err(ProgramFromElfError::other(format!(
"relocation was not expected in section '{name}': {relocation:?}",
name = section.name(),
)));
}

let Some(&origin_section_address) = base_address_for_section.get(&origin.section_index) else {
return Err(ProgramFromElfError::other(format!(
"internal error: relocation in '{name}' ({relocation_target}) refers to an origin section that doesn't have a base address assigned: origin = '{origin_name}' ({origin}), target = '{target_name}' ({target}), size = {size:?}",
name = section.name(),
origin_name = elf.section_by_index(origin.section_index).name(),
target_name = elf.section_by_index(target.section_index).name(),
)));
};

let Some(&target_section_address) = base_address_for_section.get(&target.section_index) else {
return Err(ProgramFromElfError::other(format!(
"internal error: relocation in '{name}' ({relocation_target}) refers to a target section that doesn't have a base address assigned: origin = '{origin_name}' ({origin}), target = '{target_name}' ({target}), size = {size:?}",
name = section.name(),
origin_name = elf.section_by_index(origin.section_index).name(),
target_name = elf.section_by_index(target.section_index).name(),
)));
};

let range = target_section_address.wrapping_add(target.offset)..origin_section_address.wrapping_add(origin.offset);
let data = elf.section_data_mut(relocation_target.section_index);
let mut value = range.end.wrapping_sub(range.start);
match size {
Expand Down