1 // This defines the ia32 target for UEFI systems as described in the UEFI specification. See the
2 // uefi-base module for generic UEFI options. On ia32 systems
3 // UEFI systems always run in protected-mode, have the interrupt-controller pre-configured and
4 // force a single-CPU execution.
5 // The cdecl ABI is used. It differs from the stdcall or fastcall ABI.
6 // "i686-unknown-windows" is used to get the minimal subset of windows-specific features.
8 use crate::spec::Target;
10 pub fn target() -> Target {
11 let mut base = super::uefi_msvc_base::opts();
12 base.cpu = "pentium4".into();
13 base.max_atomic_width = Some(64);
15 // We disable MMX and SSE for now, even though UEFI allows using them. Problem is, you have to
16 // enable these CPU features explicitly before their first use, otherwise their instructions
17 // will trigger an exception. Rust does not inject any code that enables AVX/MMX/SSE
18 // instruction sets, so this must be done by the firmware. However, existing firmware is known
19 // to leave these uninitialized, thus triggering exceptions if we make use of them. Which is
20 // why we avoid them and instead use soft-floats. This is also what GRUB and friends did so
22 // If you initialize FP units yourself, you can override these flags with custom linker
23 // arguments, thus giving you access to full MMX/SSE acceleration.
24 base.features = "-mmx,-sse,+soft-float".into();
26 // Use -GNU here, because of the reason below:
27 // Background and Problem:
28 // If we use i686-unknown-windows, the LLVM IA32 MSVC generates compiler intrinsic
29 // _alldiv, _aulldiv, _allrem, _aullrem, _allmul, which will cause undefined symbol.
30 // A real issue is __aulldiv() is referred by __udivdi3() - udivmod_inner!(), from
31 // https://github.com/rust-lang-nursery/compiler-builtins.
32 // As result, rust-lld generates link error finally.
34 // In rust\src\llvm-project\llvm\lib\Target\X86\X86ISelLowering.cpp,
35 // we have below code to use MSVC intrinsics. It assumes MSVC target
36 // will link MSVC library. But that is NOT true in UEFI environment.
37 // UEFI does not link any MSVC or GCC standard library.
38 // if (Subtarget.isTargetKnownWindowsMSVC() ||
39 // Subtarget.isTargetWindowsItanium()) {
40 // // Setup Windows compiler runtime calls.
41 // setLibcallName(RTLIB::SDIV_I64, "_alldiv");
42 // setLibcallName(RTLIB::UDIV_I64, "_aulldiv");
43 // setLibcallName(RTLIB::SREM_I64, "_allrem");
44 // setLibcallName(RTLIB::UREM_I64, "_aullrem");
45 // setLibcallName(RTLIB::MUL_I64, "_allmul");
46 // setLibcallCallingConv(RTLIB::SDIV_I64, CallingConv::X86_StdCall);
47 // setLibcallCallingConv(RTLIB::UDIV_I64, CallingConv::X86_StdCall);
48 // setLibcallCallingConv(RTLIB::SREM_I64, CallingConv::X86_StdCall);
49 // setLibcallCallingConv(RTLIB::UREM_I64, CallingConv::X86_StdCall);
50 // setLibcallCallingConv(RTLIB::MUL_I64, CallingConv::X86_StdCall);
52 // The compiler intrinsics should be implemented by compiler-builtins.
53 // Unfortunately, compiler-builtins has not provided those intrinsics yet. Such as:
61 // 1. Eliminate Intrinsics generation.
62 // 1.1 Choose different target to bypass isTargetKnownWindowsMSVC().
63 // 1.2 Remove the "Setup Windows compiler runtime calls" in LLVM
64 // 2. Implement Intrinsics.
65 // We evaluated all options.
66 // #2 is hard because we need implement the intrinsics (_aulldiv) generated
67 // from the other intrinsics (__udivdi3) implementation with the same
68 // functionality (udivmod_inner). If we let _aulldiv() call udivmod_inner!(),
69 // then we are in loop. We may have to find another way to implement udivmod_inner!().
70 // #1.2 may break the existing usage.
71 // #1.1 seems the simplest solution today.
72 // The IA32 -gnu calling convention is same as the one defined in UEFI specification.
73 // It uses cdecl, EAX/ECX/EDX as volatile register, and EAX/EDX as return value.
74 // We also checked the LLVM X86TargetLowering, the differences between -gnu and -msvc
75 // is fmodf(f32), longjmp() and TLS. None of them impacts the UEFI code.
76 // As a result, we choose -gnu for i686 version before those intrinsics are implemented in
77 // compiler-builtins. After compiler-builtins implements all required intrinsics, we may
78 // remove -gnu and use the default one.
80 llvm_target: "i686-unknown-windows-gnu".into(),
82 data_layout: "e-m:x-p:32:32-p270:32:32-p271:32:32-p272:64:64-\
83 i64:64-f80:32-n8:16:32-a:0:32-S32"