Add Minimal Std implementation for UEFI

Implemented modules:
1. alloc
2. os_str
3. env
4. math

Tracking Issue: #100499
API Change Proposal: rust-lang/libs-team#87

This was originally part of #100316. Since
that PR was becoming too unwieldy and cluttered, and with suggestion
from @dvdhrm, I have extracted a minimal std implementation to this PR.

Signed-off-by: Ayush Singh <ayushsingh1325@gmail.com>

Author: Ayush1325

.nlsp-settings/rust_analyzer.json

@@ -0,0 +1,3 @@
+{
+  "rust-analyzer.cargo.target": "x86_64-unknown-uefi"
+}

Cargo.lock

@@ -3006,6 +3006,27 @@ dependencies = [
  "proc-macro2",
 ]
 
+[[package]]
+name = "r-efi"
+version = "4.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9e7345c622833c6745e7b027a28aa95618813dc1f3c3de396206410267dce6f3"
+dependencies = [
+ "compiler_builtins",
+ "rustc-std-workspace-core",
+]
+
+[[package]]
+name = "r-efi-alloc"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "31d6f09fe2b6ad044bc3d2c34ce4979796581afd2f1ebc185837e02421e02fd7"
+dependencies = [
+ "compiler_builtins",
+ "r-efi",
+ "rustc-std-workspace-core",
+]
+
 [[package]]
 name = "rand"
 version = "0.8.5"
@@ -5012,6 +5033,8 @@ dependencies = [
  "panic_abort",
  "panic_unwind",
  "profiler_builtins",
+ "r-efi",
+ "r-efi-alloc",
  "rand",
  "rand_xorshift",
  "rustc-demangle",

compiler/rustc_codegen_ssa/src/base.rs

@@ -420,9 +420,11 @@ pub fn maybe_create_entry_wrapper<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
         rust_main_def_id: DefId,
         entry_type: EntryFnType,
     ) -> Bx::Function {
-        // The entry function is either `int main(void)` or `int main(int argc, char **argv)`,
-        // depending on whether the target needs `argc` and `argv` to be passed in.
-        let llfty = if cx.sess().target.main_needs_argc_argv {
+        // The entry function is either `int main(void)` or `int main(int argc, char **argv)`, or
+        // `Status efi_main(Handle hd, SystemTable *st)` depending on the target.
+        let llfty = if cx.sess().target.os.contains("uefi") {
+            cx.type_func(&[cx.type_ptr(), cx.type_ptr()], cx.type_isize())
+        } else if cx.sess().target.main_needs_argc_argv {
             cx.type_func(&[cx.type_int(), cx.type_ptr()], cx.type_int())
         } else {
             cx.type_func(&[], cx.type_int())
@@ -485,8 +487,12 @@ pub fn maybe_create_entry_wrapper<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
         };
 
         let result = bx.call(start_ty, None, None, start_fn, &args, None);
-        let cast = bx.intcast(result, cx.type_int(), true);
-        bx.ret(cast);
+        if cx.sess().target.os.contains("uefi") {
+            bx.ret(result);
+        } else {
+            let cast = bx.intcast(result, cx.type_int(), true);
+            bx.ret(cast);
+        }
 
         llfn
     }
@@ -497,7 +503,18 @@ fn get_argc_argv<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
     cx: &'a Bx::CodegenCx,
     bx: &mut Bx,
 ) -> (Bx::Value, Bx::Value) {
-    if cx.sess().target.main_needs_argc_argv {
+    if cx.sess().target.os.contains("uefi") {
+        // Params for UEFI
+        let param_handle = bx.get_param(0);
+        let param_system_table = bx.get_param(1);
+        let arg_argc = bx.const_int(cx.type_isize(), 2);
+        let arg_argv = bx.alloca(cx.type_array(cx.type_i8p(), 2), Align::ONE);
+        bx.store(param_handle, arg_argv, Align::ONE);
+        let arg_argv_el1 =
+            bx.gep(cx.type_ptr_to(cx.type_i8()), arg_argv, &[bx.const_int(cx.type_int(), 1)]);
+        bx.store(param_system_table, arg_argv_el1, Align::ONE);
+        (arg_argc, arg_argv)
+    } else if cx.sess().target.main_needs_argc_argv {
         // Params from native `main()` used as args for rust start function
         let param_argc = bx.get_param(0);
         let param_argv = bx.get_param(1);
@@ -549,7 +566,11 @@ pub fn allocator_kind_for_codegen(tcx: TyCtxt<'_>) -> Option<AllocatorKind> {
         use rustc_middle::middle::dependency_format::Linkage;
         list.iter().any(|&linkage| linkage == Linkage::Dynamic)
     });
-    if any_dynamic_crate { None } else { tcx.allocator_kind(()) }
+    if any_dynamic_crate {
+        None
+    } else {
+        tcx.allocator_kind(())
+    }
 }
 
 pub fn codegen_crate<B: ExtraBackendMethods>(

compiler/rustc_target/src/spec/uefi_msvc_base.rs

@@ -46,6 +46,7 @@ pub fn opts() -> TargetOptions {
         stack_probes: StackProbeType::Call,
         singlethread: true,
         linker: Some("rust-lld".into()),
+        entry_name: "efi_main".into(),
         ..base
     }
 }

compiler/rustc_target/src/spec/x86_64_unknown_uefi.rs

@@ -5,13 +5,14 @@
 // 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::Target;
+use crate::{abi::call::Conv, spec::Target};
 
 pub fn target() -> Target {
     let mut base = super::uefi_msvc_base::opts();
     base.cpu = "x86-64".into();
     base.plt_by_default = false;
     base.max_atomic_width = Some(64);
+    base.entry_abi = Conv::X86_64Win64;
 
     // 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

library/panic_abort/src/lib.rs

@@ -45,6 +45,7 @@ pub unsafe fn __rust_start_panic(_payload: &mut dyn PanicPayload) -> u32 {
         } else if #[cfg(any(target_os = "hermit",
                             all(target_vendor = "fortanix", target_env = "sgx"),
                             target_os = "xous"
+                            target_os = "uefi",
         ))] {
             unsafe fn abort() -> ! {
                 // call std::sys::abort_internal

library/std/Cargo.toml

@@ -48,6 +48,10 @@ hermit-abi = { version = "0.3.2", features = ['rustc-dep-of-std'], public = true
 [target.'cfg(target_os = "wasi")'.dependencies]
 wasi = { version = "0.11.0", features = ['rustc-dep-of-std'], default-features = false }
 
+[target.'cfg(target_os = "uefi")'.dependencies]
+r-efi = { version = "4.1.0", features = ['rustc-dep-of-std', 'efiapi']}
+r-efi-alloc = { version = "1.0.0", features = ['rustc-dep-of-std']}
+
 [features]
 backtrace = [
   "gimli-symbolize",

library/std/build.rs

@@ -39,6 +39,7 @@ fn main() {
         || target.contains("nto")
         || target.contains("xous")
         || target.contains("hurd")
+        || target.contains("uefi")
         // See src/bootstrap/synthetic_targets.rs
         || env::var("RUSTC_BOOTSTRAP_SYNTHETIC_TARGET").is_ok()
     {
@@ -51,7 +52,7 @@ fn main() {
         // - mipsel-sony-psp
         // - nvptx64-nvidia-cuda
         // - arch=avr
-        // - uefi (x86_64-unknown-uefi, i686-unknown-uefi)
+        // - tvos (aarch64-apple-tvos, x86_64-apple-tvos)
         // - JSON targets
         // - Any new targets that have not been explicitly added above.
         println!("cargo:rustc-cfg=feature=\"restricted-std\"");

library/std/src/lib.rs

@@ -263,7 +263,6 @@
 #![cfg_attr(target_os = "xous", feature(slice_ptr_len))]
 //
 // Language features:
-// tidy-alphabetical-start
 #![feature(alloc_error_handler)]
 #![feature(allocator_internals)]
 #![feature(allow_internal_unsafe)]

library/std/src/os/mod.rs

@@ -142,6 +142,8 @@ pub mod solid;
 #[cfg(target_os = "tvos")]
 #[path = "ios/mod.rs"]
 pub(crate) mod tvos;
+#[cfg(target_os = "uefi")]
+pub mod uefi;
 #[cfg(target_os = "vita")]
 pub mod vita;
 #[cfg(target_os = "vxworks")]