Function translate_eh_pe

cranelift/object/src/unwind.rs:163–218

Translate a gimli `.eh_frame` relocation request into the `object` crate's relocation flags for the target binary format. `eh_pe` is `None` for non-pointer relocations (rare in `.eh_frame`); in that case we treat the request as an absolute pointer of the requested width.

(
    eh_pe: Option<gimli::constants::DwEhPe>,
    size: u8,
    format: BinaryFormat,
)

/// `eh_pe` is `None` for non-pointer relocations (rare in `.eh_frame`); in that
/// case we treat the request as an absolute pointer of the requested width.
fn translate_eh_pe(
    eh_pe: Option<gimli::constants::DwEhPe>,
    size: u8,
    format: BinaryFormat,
) -> Result<RelocationFlags> {
    use gimli::constants::*;

    let Some(pe) = eh_pe else {
        return Ok(RelocationFlags::Generic {
            kind: RelocationKind::Absolute,
            encoding: RelocationEncoding::Generic,
            size: size * 8,
        });
    };

    let application = pe.application();
    let kind = if application == DW_EH_PE_absptr {
        RelocationKind::Absolute
    } else if application == DW_EH_PE_pcrel {
        RelocationKind::Relative
    } else {
        return Err(anyhow!(
            "unsupported eh_frame pointer application {application:?}"
        ));
    };
    let format_byte = pe.format();
    let bit_size = if format_byte == DW_EH_PE_absptr {
        size * 8
    } else if format_byte == DW_EH_PE_udata2 || format_byte == DW_EH_PE_sdata2 {
        16
    } else if format_byte == DW_EH_PE_udata4 || format_byte == DW_EH_PE_sdata4 {
        32
    } else if format_byte == DW_EH_PE_udata8 || format_byte == DW_EH_PE_sdata8 {
        64
    } else {
        return Err(anyhow!(
            "unsupported eh_frame pointer format {format_byte:?}"
        ));
    };

    // Mach-O encodes PC-relative `.eh_frame` references as a SUBTRACTOR /
    // UNSIGNED relocation pair, which is out of scope here. Surface a clear
    // error rather than emitting the wrong relocation.
    //
    // TODO: arm64 Mach-O `__TEXT,__eh_frame` is feasible via that reloc pair;
    // see rust-lang/rustc_codegen_cranelift#1634 for the approach.
    if matches!(format, BinaryFormat::MachO) && kind == RelocationKind::Relative {
        return Err(anyhow!("Mach-O .eh_frame emission is not yet supported"));
    }

    Ok(RelocationFlags::Generic {
        kind,
        encoding: RelocationEncoding::Generic,
        size: bit_size,
    })
}

#[cfg(test)]