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Merged
davidlattimore merged 1 commit into from
Jul 1, 2025
Merged

Use segment rather than section layout for TLS addresses #975

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12 changes: 2 additions & 10 deletions libwild/src/elf_writer.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1273,11 +1273,7 @@ fn write_symbols(
let mut symbol_value = res.value_for_symbol_table();

if sym.st_type() == object::elf::STT_TLS {
let tls_start_address = layout
.segment_layouts
.tls_start_address
.context("Writing TLS variable to symtab, but we don't have a TLS segment")?;
symbol_value -= tls_start_address;
symbol_value -= layout.tls_start_address();
}

symbol_writer
Expand Down Expand Up @@ -2945,11 +2941,7 @@ fn write_regular_object_dynamic_symbol_definition(
})?;
let mut symbol_value = resolution.raw_value;
if sym.st_type() == object::elf::STT_TLS {
let tls_start_address = layout
.segment_layouts
.tls_start_address
.context("Writing TLS variable to symtab, but we don't have a TLS segment")?;
symbol_value -= tls_start_address;
symbol_value -= layout.tls_start_address();
}
dynamic_symbol_writer
.copy_symbol(sym, name, output_section_id, symbol_value)
Expand Down
49 changes: 25 additions & 24 deletions libwild/src/layout.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -624,7 +624,7 @@ pub(crate) struct SegmentLayouts {
/// The layout of each of our segments. Segments containing no active output sections will have
/// been filtered, so don't try to index this by our internal segment IDs.
pub(crate) segments: Vec<SegmentLayout>,
pub(crate) tls_start_address: Option<u64>,
pub(crate) tls_layout: Option<OutputRecordLayout>,
}

#[derive(Default, Clone)]
Expand Down Expand Up @@ -1774,25 +1774,26 @@ impl<'data> Layout<'data> {

pub(crate) fn tls_start_address(&self) -> u64 {
// If we don't have a TLS segment then the value we return won't really matter.
self.segment_layouts.tls_start_address.unwrap_or(0)
self.segment_layouts
.tls_layout
.as_ref()
.map_or(0, |seg| seg.mem_offset)
}

/// Returns the memory address of the end of the TLS segment including any padding required to
/// make sure that the TCB will be usize-aligned.
pub(crate) fn tls_end_address(&self) -> u64 {
let tbss = self.section_layouts.get(output_section_id::TBSS);
let tdata = self.section_layouts.get(output_section_id::TDATA);
let tls_end = tbss.mem_offset + tbss.mem_size;
let alignment = tbss.alignment.max(tdata.alignment);
alignment.align_up(tls_end)
self.segment_layouts.tls_layout.as_ref().map_or(0, |seg| {
seg.alignment.align_up(seg.mem_offset + seg.mem_size)
})
}

/// Returns the memory address of the start of the TLS segment used by the AArch64.
pub(crate) fn tls_start_address_aarch64(&self) -> u64 {
let tdata = self.section_layouts.get(output_section_id::TDATA);
// Two words at TP are reserved by the arch.
let tls_start = tdata.mem_offset - 2 * 8;
tdata.alignment.align_down(tls_start)
self.segment_layouts.tls_layout.as_ref().map_or(0, |seg| {
// Two words at TP are reserved by the arch.
seg.alignment.align_down(seg.mem_offset - 2 * 8)
})
}

pub(crate) fn layout_data(&self) -> linker_layout::Layout {
Expand Down Expand Up @@ -2066,35 +2067,35 @@ fn compute_segment_layout(
complete.sort_by_key(|r| r.segment_id);

assert_eq!(complete.len(), program_segments.len());
let mut tls_start_address = None;
let mut tls_layout = None;

let mut segments: Vec<SegmentLayout> = header_info
.active_segment_ids
.iter()
.map(|&id| {
let r = &complete[id.as_usize()];

let sizes = OutputRecordLayout {
file_size: r.file_end - r.file_start,
mem_size: r.mem_end - r.mem_start,
alignment: r.alignment,
file_offset: r.file_start,
mem_offset: r.mem_start,
};

if program_segments.is_tls_segment(id) {
tls_start_address = Some(r.mem_start);
tls_layout = Some(sizes);
}

SegmentLayout {
id,
sizes: OutputRecordLayout {
file_size: r.file_end - r.file_start,
mem_size: r.mem_end - r.mem_start,
alignment: r.alignment,
file_offset: r.file_start,
mem_offset: r.mem_start,
},
}
SegmentLayout { id, sizes }
})
.collect();

segments.sort_by_key(|s| program_segments.order_key(s.id, s.sizes.mem_offset));

Ok(SegmentLayouts {
segments,
tls_start_address,
tls_layout,
})
}

Expand Down