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feat: support using an expression when setting the location counter #2005

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feat: support using an expression when setting the location counter #2005

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dcaf9bc
feat: use an expression for location type
vishruth-thimmaiah May 31, 2026
5e64b65
fix: use updated offset when `.` is set to a new value
vishruth-thimmaiah May 31, 2026
522eea0
fix: resolve shndx properly
vishruth-thimmaiah May 31, 2026
216c952
fix: correctly set base_address
vishruth-thimmaiah May 31, 2026
17f9f6d
fix: formatting
vishruth-thimmaiah Jun 1, 2026
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2 changes: 1 addition & 1 deletion libwild/src/elf.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1830,7 +1830,7 @@ impl platform::Platform for Elf {
output_kind: OutputKind,
output_sections: &OutputSections<'data, Self>,
secondary: &OutputSectionMap<Vec<OutputSectionId>>,
) -> (OutputOrder, ProgramSegments<Self::ProgramSegmentDef>) {
) -> (OutputOrder<'data>, ProgramSegments<Self::ProgramSegmentDef>) {
let mut builder = OutputOrderBuilder::<Self>::new(output_kind, output_sections, secondary);

builder.add_section(output_section_id::FILE_HEADER);
Expand Down
11 changes: 11 additions & 0 deletions libwild/src/elf_writer.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -4447,6 +4447,17 @@ fn get_defsym_attributes(
}
SymbolLoc::FirstSection => 1,
SymbolLoc::None => return Ok((object::elf::SHN_ABS.into(), object::elf::STT_NOTYPE)),
SymbolLoc::Expression(_, os) => {
if let Some(os) = os {
let os = layout.output_sections.primary_output_section(os);
layout
.output_sections
.output_index_of_section(os)
.unwrap_or(0)
} else {
1
}
}
};
Ok((SymbolSection::Index(shndx), object::elf::STT_NOTYPE))
}
Expand Down
13 changes: 7 additions & 6 deletions libwild/src/expression_eval.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -45,7 +45,7 @@ pub(crate) fn evaluate_assertions<'data, P: Platform>(
let line = line_number(parsed.file_bytes, assertion.remainder);
let result = evaluate_expression(
&assertion.expression,
SymbolLoc::None,
&SymbolLoc::None,
section_layouts,
output_sections,
&parsed.memory_regions,
Expand Down Expand Up @@ -80,7 +80,7 @@ pub(crate) fn evaluate_assertions<'data, P: Platform>(

pub(crate) fn evaluate_expression<'data, P: Platform>(
expr: &Expression<'data>,
expr_loc: SymbolLoc,
expr_loc: &SymbolLoc<'data>,
section_layouts: &OutputSectionMap<OutputRecordLayout>,
output_sections: &OutputSections<'data, P>,
memory_regions: &[MemoryRegion<'data>],
Expand All @@ -105,12 +105,13 @@ pub(crate) fn evaluate_expression<'data, P: Platform>(
Expression::Number(n) => Ok(*n),

Expression::LocationCounter => match expr_loc {
SymbolLoc::SectionStart(id) => Ok(section_layouts.get(id).mem_offset),
SymbolLoc::SectionStart(id) => Ok(section_layouts.get(*id).mem_offset),
SymbolLoc::SectionEnd(id) => {
let layout = section_layouts.get(id);
let layout = section_layouts.get(*id);
Ok(layout.mem_offset + layout.mem_size)
}
SymbolLoc::FirstSection | SymbolLoc::None => Ok(0),
SymbolLoc::Expression(expr, _) => eval!(expr),
},

Expression::Symbol(name) => symbol_resolution_callback(name),
Expand Down Expand Up @@ -280,7 +281,7 @@ mod tests {
with_dummy_context(|layouts, sections, symbol_db| {
evaluate_expression::<Elf>(
expr,
SymbolLoc::None,
&SymbolLoc::None,
layouts,
sections,
&[],
Expand Down Expand Up @@ -656,7 +657,7 @@ mod tests {
let eval = |expr: &Expression<'static>| {
evaluate_expression::<Elf>(
expr,
SymbolLoc::None,
&SymbolLoc::None,
layouts,
sections,
&regions,
Expand Down
117 changes: 84 additions & 33 deletions libwild/src/layout.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,7 @@ use crate::input_data::InputRef;
use crate::input_data::PRELUDE_FILE_ID;
use crate::input_section_id::SectionIdRange;
use crate::layout_rules::SectionKind;
use crate::linker_script::Expression;
use crate::output_section_id;
use crate::output_section_id::OrderEvent;
use crate::output_section_id::OutputOrder;
Expand Down Expand Up @@ -232,13 +233,28 @@ pub fn compute<'data, P: Platform, A: Arch<Platform = P>>(
&symbol_db,
);

let memory_regions: Vec<crate::linker_script::MemoryRegion<'_>> = symbol_db
.groups
.iter()
.filter_map(|g| {
if let crate::grouping::Group::LinkerScripts(scripts) = g {
Some(scripts)
} else {
None
}
})
.flatten()
.flat_map(|s| s.parsed.memory_regions.iter().cloned())
.collect();

let mut section_part_layouts = layout_section_parts::<A::Platform>(
&section_part_sizes,
&output_sections,
&program_segments,
&output_order,
symbol_db.args,
);
&symbol_db,
&memory_regions,
)?;

if symbol_db.args.should_relax() && A::supports_size_reduction_relaxations() {
perform_iterative_relaxation::<A>(
Expand All @@ -250,7 +266,8 @@ pub fn compute<'data, P: Platform, A: Arch<Platform = P>>(
&output_order,
&symbol_db,
&per_symbol_flags,
);
&memory_regions,
)?;
}

if let Some((record, last_part_id)) = section_part_layouts
Expand Down Expand Up @@ -474,7 +491,7 @@ fn update_defsym_symbol_resolution<'data, P: Platform>(
if let SymbolPlacement::Redirect(redirect) = &def_info.placement {
let value = crate::expression_eval::evaluate_expression(
&redirect.expression,
redirect.loc,
&redirect.loc,
section_layouts,
output_sections,
memory_regions,
Expand Down Expand Up @@ -633,7 +650,7 @@ pub struct Layout<'data, P: Platform> {
pub(crate) segment_layouts: SegmentLayouts,
pub(crate) output_sections: OutputSections<'data, P>,
pub(crate) program_segments: ProgramSegments<P::ProgramSegmentDef>,
pub(crate) output_order: OutputOrder,
pub(crate) output_order: OutputOrder<'data>,
pub(crate) non_addressable_counts: P::NonAddressableCounts,
pub(crate) merged_strings: OutputSectionMap<MergedStringsSection<'data>>,
pub(crate) merged_string_start_addresses: MergedStringStartAddresses,
Expand Down Expand Up @@ -1317,7 +1334,7 @@ pub(crate) struct FinaliseLayoutResources<'scope, 'data, P: Platform> {
pub(crate) symbol_db: &'scope SymbolDb<'data, P>,
pub(crate) per_symbol_flags: &'scope PerSymbolFlags,
output_sections: &'scope OutputSections<'data, P>,
output_order: &'scope OutputOrder,
output_order: &'scope OutputOrder<'data>,
pub(crate) section_layouts: &'scope OutputSectionMap<OutputRecordLayout>,
merged_string_start_addresses: &'scope MergedStringStartAddresses,
merged_strings: &'scope OutputSectionMap<MergedStringsSection<'data>>,
Expand Down Expand Up @@ -1675,10 +1692,10 @@ fn compute_symbols_and_layouts<'data, P: Platform>(
.collect()
}

fn compute_segment_layout<P: Platform>(
fn compute_segment_layout<'data, P: Platform>(
section_layouts: &OutputSectionMap<OutputRecordLayout>,
output_sections: &OutputSections<P>,
output_order: &OutputOrder,
output_order: &OutputOrder<'data>,
program_segments: &ProgramSegments<P::ProgramSegmentDef>,
header_info: &HeaderInfo,
args: &P::Args,
Expand Down Expand Up @@ -1827,7 +1844,7 @@ fn compute_segment_layout<P: Platform>(
fn compute_total_section_part_sizes<'data, P: Platform>(
group_states: &mut [GroupState<'data, P>],
output_sections: &mut OutputSections<P>,
output_order: &OutputOrder,
output_order: &OutputOrder<'data>,
program_segments: &ProgramSegments<P::ProgramSegmentDef>,
per_symbol_flags: &mut PerSymbolFlags,
must_keep_sections: OutputSectionMap<bool>,
Expand Down Expand Up @@ -2941,7 +2958,7 @@ impl<'data, P: Platform> PreludeLayoutState<'data, P> {
total_sizes: &mut OutputSectionPartMap<u64>,
must_keep_sections: OutputSectionMap<bool>,
output_sections: &mut OutputSections<P>,
output_order: &OutputOrder,
output_order: &OutputOrder<'data>,
program_segments: &ProgramSegments<P::ProgramSegmentDef>,
per_symbol_flags: &mut PerSymbolFlags,
resources: &FinaliseSizesResources<'data, '_, P>,
Expand Down Expand Up @@ -3053,7 +3070,7 @@ impl<'data, P: Platform> PreludeLayoutState<'data, P> {
must_keep_sections: OutputSectionMap<bool>,
output_sections: &mut OutputSections<P>,
program_segments: &ProgramSegments<P::ProgramSegmentDef>,
output_order: &OutputOrder,
output_order: &OutputOrder<'data>,
resources: &FinaliseSizesResources<'data, '_, P>,
symbol_flags: &PerSymbolFlags,
) {
Expand Down Expand Up @@ -4730,12 +4747,13 @@ fn perform_iterative_relaxation<'data, A: Arch>(
group_states: &mut [GroupState<'data, A::Platform>],
section_part_sizes: &mut OutputSectionPartMap<u64>,
section_part_layouts: &mut OutputSectionPartMap<OutputRecordLayout>,
output_sections: &OutputSections<A::Platform>,
output_sections: &OutputSections<'data, A::Platform>,
program_segments: &ProgramSegments<<A::Platform as Platform>::ProgramSegmentDef>,
output_order: &OutputOrder,
output_order: &OutputOrder<'data>,
symbol_db: &SymbolDb<'data, A::Platform>,
per_symbol_flags: &PerSymbolFlags,
) {
memory_regions: &[crate::linker_script::MemoryRegion<'data>],
) -> Result {
timing_phase!("Iterative relaxation");

let mut rescan_sections: Option<RescanSections> = None;
Expand Down Expand Up @@ -4789,18 +4807,22 @@ fn perform_iterative_relaxation<'data, A: Arch>(
output_sections,
program_segments,
output_order,
symbol_db.args,
);
symbol_db,
memory_regions,
)?;
}
Ok(())
}

fn layout_section_parts<P: Platform>(
fn layout_section_parts<'data, P: Platform>(
sizes: &OutputSectionPartMap<u64>,
output_sections: &OutputSections<P>,
output_sections: &OutputSections<'data, P>,
program_segments: &ProgramSegments<P::ProgramSegmentDef>,
output_order: &OutputOrder,
args: &P::Args,
) -> OutputSectionPartMap<OutputRecordLayout> {
output_order: &OutputOrder<'data>,
symbol_db: &SymbolDb<'data, P>,
memory_regions: &[crate::linker_script::MemoryRegion<'data>],
) -> Result<OutputSectionPartMap<OutputRecordLayout>> {
let args = symbol_db.args;
let segment_alignments = compute_segment_alignments::<P>(
sizes,
program_segments,
Expand All @@ -4809,8 +4831,26 @@ fn layout_section_parts<P: Platform>(
output_sections,
);

// Create an empty section layout for now, until we can support using linker script
// commands.
let empty_section_layouts = OutputSectionMap::with_size(output_sections.num_sections());

let expression_eval = |expr: &Expression<'data>| {
crate::expression_eval::evaluate_expression(
expr,
&crate::parsing::SymbolLoc::None,
&empty_section_layouts,
output_sections,
memory_regions,
symbol_db,
&|_| {
bail!("Symbols with the set location operation are not yet supported.");
},
)
};

let mut file_offset = 0;
let mut mem_offset = output_sections.base_address;
let mut mem_offset = expression_eval(&output_sections.base_address)?;
let mut nonalloc_mem_offsets: OutputSectionMap<u64> =
OutputSectionMap::with_size(output_sections.num_sections());
let mut reloc_alloc_mem_offsets: OutputSectionMap<u64> =
Expand All @@ -4822,18 +4862,18 @@ fn layout_section_parts<P: Platform>(

for event in output_order {
match event {
OrderEvent::SetLocation(location) => {
pending_location = Some(location);
OrderEvent::SetLocation(expr) => {
pending_location = Some(expr);
}
OrderEvent::SegmentStart(segment_id) => {
if program_segments.is_load_segment(segment_id) {
let segment_alignment = segment_alignments
.get(&segment_id)
.copied()
.unwrap_or_else(|| args.loadable_segment_alignment());
if let Some(location) = pending_location.take() {
if let Some(expr) = pending_location.take() {
// The OrderEvent::SetLocation is ELF-specific only.
mem_offset = location.address;
mem_offset = expression_eval(&expr)?;
file_offset =
segment_alignment.align_modulo(mem_offset, file_offset as u64) as usize;
} else {
Expand All @@ -4856,8 +4896,8 @@ fn layout_section_parts<P: Platform>(
let section_info = output_sections.output_info(section_id);
let part_id_range = section_id.part_id_range();
let max_alignment = sizes.max_alignment(part_id_range.clone(), output_sections);
if let Some(location) = section_info.location {
mem_offset = location.address;
if let Some(ref expr) = section_info.location {
mem_offset = expression_eval(expr)?;
}

records_out[part_id_range.clone()]
Expand Down Expand Up @@ -4945,15 +4985,15 @@ fn layout_section_parts<P: Platform>(
};
}

records_out
Ok(records_out)
}

/// Computes the maximum alignment for each LOAD segment by examining the alignments of all sections
/// that will be placed in that segment.
fn compute_segment_alignments<P: Platform>(
fn compute_segment_alignments<'data, P: Platform>(
sizes: &OutputSectionPartMap<u64>,
program_segments: &ProgramSegments<P::ProgramSegmentDef>,
output_order: &OutputOrder,
output_order: &OutputOrder<'data>,
args: &P::Args,
output_sections: &OutputSections<P>,
) -> HashMap<ProgramSegmentId, Alignment> {
Expand Down Expand Up @@ -5241,13 +5281,24 @@ fn test_no_disallowed_overlaps() {
}
let section_part_sizes = output_sections.new_part_map::<u64>().map(|_, _| 7);

let output_kind = crate::output_kind::OutputKind::StaticExecutable(
crate::args::RelocationModel::NonRelocatable,
);
let arena = colosseum::sync::Arena::new();
let auxiliary = crate::input_data::AuxiliaryFiles::new(&args, &arena).unwrap();
let herd = Default::default();
let symbol_db =
crate::symbol_db::SymbolDb::<Elf>::new(&args, output_kind, &auxiliary, &herd).unwrap();

let section_part_layouts = layout_section_parts::<Elf>(
&section_part_sizes,
&output_sections,
&program_segments,
&output_order,
&args,
);
&symbol_db,
&[],
)
.unwrap();

let section_layouts = layout_sections(&output_sections, &section_part_layouts);

Expand Down
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