rust/src/librustc_target/spec/x86_64_unknown_uefi.rs

// This defines the amd64 target for UEFI systems as described in the UEFI specification. See the
// uefi-base module for generic UEFI options. On x86_64 systems (mostly called "x64" in the spec)
// UEFI systems always run in long-mode, have the interrupt-controller pre-configured and force a
// single-CPU execution.
// The win64 ABI is used. It differs from the sysv64 ABI, so we must use a windows target with
// LLVM. "x86_64-unknown-windows" is used to get the minimal subset of windows-specific features.

use crate::spec::{LinkerFlavor, LldFlavor, Target, TargetResult};

pub fn target() -> TargetResult {
    let mut base = super::uefi_base::opts();
    base.cpu = "x86-64".to_string();
    base.max_atomic_width = Some(64);

    // We disable MMX and SSE for now. UEFI does not prevent these from being used, but there have
    // been reports to GRUB that some firmware does not initialize the FP exception handlers
    // properly. Therefore, using FP coprocessors will end you up at random memory locations when
    // you throw FP exceptions.
    // To be safe, we disable them for now and force soft-float. This can be revisited when we
    // have more test coverage. Disabling FP served GRUB well so far, so it should be good for us
    // as well.
    base.features = "-mmx,-sse,+soft-float".to_string();

    // UEFI systems run without a host OS, hence we cannot assume any code locality. We must tell
    // LLVM to expect code to reference any address in the address-space. The "large" code-model
    // places no locality-restrictions, so it fits well here.
    base.code_model = Some("large".to_string());

    // UEFI mostly mirrors the calling-conventions used on windows. In case of x86-64 this means
    // small structs will be returned as int. This shouldn't matter much, since the restrictions
    // placed by the UEFI specifications forbid any ABI to return structures.
    base.abi_return_struct_as_int = true;

    Ok(Target {
        llvm_target: "x86_64-unknown-windows".to_string(),
        target_endian: "little".to_string(),
        target_pointer_width: "64".to_string(),
        target_c_int_width: "32".to_string(),
        data_layout: "e-m:w-i64:64-f80:128-n8:16:32:64-S128".to_string(),
        target_os: "uefi".to_string(),
        target_env: "".to_string(),
        target_vendor: "unknown".to_string(),
        arch: "x86_64".to_string(),
        linker_flavor: LinkerFlavor::Lld(LldFlavor::Link),

        options: base,
    })
}