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Split TlsLdToLocalExec relaxation into two #279

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merged 1 commit into from
Jan 6, 2025
Merged

Split TlsLdToLocalExec relaxation into two #279

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8 changes: 8 additions & 0 deletions libwild/src/x86_64.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -254,6 +254,14 @@ impl crate::arch::Relaxation for Relaxation {
}
object::elf::R_X86_64_TLSLD if output_kind.is_executable() => {
if section_bytes.get(offset - 3..offset)? == [0x48, 0x8d, 0x3d] {
if section_bytes.get(offset + 4..offset + 6) == Some(&[0x48, 0xb8]) {
// The previous instruction was 64 bit, so we use a slightly different
// relaxation with extra padding.
return create(
RelaxationKind::TlsLdToLocalExec64,
object::elf::R_X86_64_NONE,
);
}
return create(RelaxationKind::TlsLdToLocalExec, object::elf::R_X86_64_NONE);
}
}
Expand Down
33 changes: 17 additions & 16 deletions linker-utils/src/x86_64.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -36,6 +36,10 @@ pub enum RelaxationKind {
/// Transform local dynamic (LD) into local exec.
TlsLdToLocalExec,

/// Transform local dynamic (LD) into local exec with extra padding because the previous
/// instruction was 64 bit.
TlsLdToLocalExec64,

/// Transform general dynamic (GD) into initial exec
TlsGdToInitialExec,
}
Expand Down Expand Up @@ -119,22 +123,19 @@ impl RelaxationKind {
*next_modifier = RelocationModifier::SkipNextRelocation;
}
RelaxationKind::TlsLdToLocalExec => {
// Transforms to: `mov %fs:0x0,%rax` with some amount of padding depending on
// whether the subsequent instruction is 64 bit (first) or 32 bit (second).
if section_bytes.get(offset + 4..offset + 6) == Some(&[0x48, 0xb8]) {
section_bytes[offset - 3..offset + 19].copy_from_slice(&[
// nopw (%rax,%rax)
0x66, 0x66, 0x66, 0x66, 0x2e, 0x0f, 0x1f, 0x84, 0, 0, 0, 0, 0,
// mov %fs:0,%rax
0x64, 0x48, 0x8b, 0x04, 0x25, 0, 0, 0, 0,
]);
*offset_in_section += 15;
} else {
section_bytes[offset - 3..offset + 9].copy_from_slice(&[
0x66, 0x66, 0x66, 0x64, 0x48, 0x8b, 0x04, 0x25, 0, 0, 0, 0,
]);
*offset_in_section += 5;
}
section_bytes[offset - 3..offset + 9]
.copy_from_slice(&[0x66, 0x66, 0x66, 0x64, 0x48, 0x8b, 0x04, 0x25, 0, 0, 0, 0]);
*offset_in_section += 5;
*next_modifier = RelocationModifier::SkipNextRelocation;
}
RelaxationKind::TlsLdToLocalExec64 => {
section_bytes[offset - 3..offset + 19].copy_from_slice(&[
// nopw (%rax,%rax)
0x66, 0x66, 0x66, 0x66, 0x2e, 0x0f, 0x1f, 0x84, 0, 0, 0, 0, 0,
// mov %fs:0,%rax
0x64, 0x48, 0x8b, 0x04, 0x25, 0, 0, 0, 0,
]);
*offset_in_section += 15;
*next_modifier = RelocationModifier::SkipNextRelocation;
}
RelaxationKind::NoOp => {}
Expand Down