diff options
Diffstat (limited to 'compiler/rustc_target/src/spec/i686_unknown_uefi.rs')
| -rw-r--r-- | compiler/rustc_target/src/spec/i686_unknown_uefi.rs | 89 |
1 files changed, 89 insertions, 0 deletions
diff --git a/compiler/rustc_target/src/spec/i686_unknown_uefi.rs b/compiler/rustc_target/src/spec/i686_unknown_uefi.rs new file mode 100644 index 000000000..a2e42c5e6 --- /dev/null +++ b/compiler/rustc_target/src/spec/i686_unknown_uefi.rs @@ -0,0 +1,89 @@ +// This defines the ia32 target for UEFI systems as described in the UEFI specification. See the +// uefi-base module for generic UEFI options. On ia32 systems +// UEFI systems always run in protected-mode, have the interrupt-controller pre-configured and +// force a single-CPU execution. +// The cdecl ABI is used. It differs from the stdcall or fastcall ABI. +// "i686-unknown-windows" is used to get the minimal subset of windows-specific features. + +use crate::spec::Target; + +pub fn target() -> Target { + let mut base = super::uefi_msvc_base::opts(); + base.cpu = "pentium4".into(); + base.max_atomic_width = Some(64); + + // We disable MMX and SSE for now, even though UEFI allows using them. Problem is, you have to + // enable these CPU features explicitly before their first use, otherwise their instructions + // will trigger an exception. Rust does not inject any code that enables AVX/MMX/SSE + // instruction sets, so this must be done by the firmware. However, existing firmware is known + // to leave these uninitialized, thus triggering exceptions if we make use of them. Which is + // why we avoid them and instead use soft-floats. This is also what GRUB and friends did so + // far. + // If you initialize FP units yourself, you can override these flags with custom linker + // arguments, thus giving you access to full MMX/SSE acceleration. + base.features = "-mmx,-sse,+soft-float".into(); + + // Use -GNU here, because of the reason below: + // Background and Problem: + // If we use i686-unknown-windows, the LLVM IA32 MSVC generates compiler intrinsic + // _alldiv, _aulldiv, _allrem, _aullrem, _allmul, which will cause undefined symbol. + // A real issue is __aulldiv() is referred by __udivdi3() - udivmod_inner!(), from + // https://github.com/rust-lang-nursery/compiler-builtins. + // As result, rust-lld generates link error finally. + // Root-cause: + // In rust\src\llvm-project\llvm\lib\Target\X86\X86ISelLowering.cpp, + // we have below code to use MSVC intrinsics. It assumes MSVC target + // will link MSVC library. But that is NOT true in UEFI environment. + // UEFI does not link any MSVC or GCC standard library. + // if (Subtarget.isTargetKnownWindowsMSVC() || + // Subtarget.isTargetWindowsItanium()) { + // // Setup Windows compiler runtime calls. + // setLibcallName(RTLIB::SDIV_I64, "_alldiv"); + // setLibcallName(RTLIB::UDIV_I64, "_aulldiv"); + // setLibcallName(RTLIB::SREM_I64, "_allrem"); + // setLibcallName(RTLIB::UREM_I64, "_aullrem"); + // setLibcallName(RTLIB::MUL_I64, "_allmul"); + // setLibcallCallingConv(RTLIB::SDIV_I64, CallingConv::X86_StdCall); + // setLibcallCallingConv(RTLIB::UDIV_I64, CallingConv::X86_StdCall); + // setLibcallCallingConv(RTLIB::SREM_I64, CallingConv::X86_StdCall); + // setLibcallCallingConv(RTLIB::UREM_I64, CallingConv::X86_StdCall); + // setLibcallCallingConv(RTLIB::MUL_I64, CallingConv::X86_StdCall); + // } + // The compiler intrinsics should be implemented by compiler-builtins. + // Unfortunately, compiler-builtins has not provided those intrinsics yet. Such as: + // i386/divdi3.S + // i386/lshrdi3.S + // i386/moddi3.S + // i386/muldi3.S + // i386/udivdi3.S + // i386/umoddi3.S + // Possible solution: + // 1. Eliminate Intrinsics generation. + // 1.1 Choose different target to bypass isTargetKnownWindowsMSVC(). + // 1.2 Remove the "Setup Windows compiler runtime calls" in LLVM + // 2. Implement Intrinsics. + // We evaluated all options. + // #2 is hard because we need implement the intrinsics (_aulldiv) generated + // from the other intrinsics (__udivdi3) implementation with the same + // functionality (udivmod_inner). If we let _aulldiv() call udivmod_inner!(), + // then we are in loop. We may have to find another way to implement udivmod_inner!(). + // #1.2 may break the existing usage. + // #1.1 seems the simplest solution today. + // The IA32 -gnu calling convention is same as the one defined in UEFI specification. + // It uses cdecl, EAX/ECX/EDX as volatile register, and EAX/EDX as return value. + // We also checked the LLVM X86TargetLowering, the differences between -gnu and -msvc + // is fmodf(f32), longjmp() and TLS. None of them impacts the UEFI code. + // As a result, we choose -gnu for i686 version before those intrinsics are implemented in + // compiler-builtins. After compiler-builtins implements all required intrinsics, we may + // remove -gnu and use the default one. + Target { + llvm_target: "i686-unknown-windows-gnu".into(), + pointer_width: 32, + data_layout: "e-m:x-p:32:32-p270:32:32-p271:32:32-p272:64:64-\ + i64:64-f80:32-n8:16:32-a:0:32-S32" + .into(), + arch: "x86".into(), + + options: base, + } +} |