Auto merge of #105861 - Ayush1325:uefi-std-minimial, r=workingjubilee

Add Minimal Std implementation for UEFI

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

# Related Links
Tracking Issue: https://github.com/rust-lang/rust/issues/100499
API Change Proposal: https://github.com/rust-lang/libs-team/issues/87

# Additional Information
This was originally part of https://github.com/rust-lang/rust/pull/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.

The example in `src/doc/rustc/src/platform-support/unknown-uefi.md` has been tested for `x86_64-unknown-uefi` and `i686-unknown-uefi` in OVMF. It would be great if someone more familiar with AARCH64 can help with testing for that target.

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

1 files changed, 22 insertions, 6 deletions

diff --git a/compiler/rustc_codegen_ssa/src/base.rs b/compiler/rustc_codegen_ssa/src/base.rs
index cd19885faa0..6c51dffedbf 100644
--- a/compiler/rustc_codegen_ssa/src/base.rs
+++ b/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
+        // `usize efi_main(void *handle, void *system_table)` 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 +503,17 @@ 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_ptr(), 2), Align::ONE);
+        bx.store(param_handle, arg_argv, Align::ONE);
+        let arg_argv_el1 = bx.gep(cx.type_ptr(), 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);