squashed changes to tests

correctly emit `.hidden`

this test was added in rust-lang#105193

but actually NO_COVERAGE is no longer a thing in the compiler. Sadly,
the link to the issue is broken, so I don't know what the problem was
originally, but I don't think this is relevant any more with the global
asm approach

rename test file

because it now specifically checks for directives only used by
non-macos, non-windows x86_64

add codegen tests for 4 interesting platforms

add codegen test for the `#[instruction_set]` attribute

add test for `#[link_section]`

use `tcx.codegen_fn_attrs` to get attribute info

Fix rust-lang#124375

inline const monomorphization/evaluation

getting rid of FunctionCx

mark naked functions as `InstantiatedMode::GloballyShared`

this makes sure that the function prototype is defined correctly, and we don't see LLVM complaining about a global value with invalid linkage

monomorphize type given to `SymFn`

remove hack that always emits `.globl`

monomorphize type given to `Const`

remove `linkage_directive`

make naked functions always have external linkage

mark naked functions as `#[inline(never)]`

add test file for functional generics/const/impl/trait usage of naked functions

Author: folkertdev

compiler/rustc_codegen_llvm/src/attributes.rs

@@ -395,17 +395,9 @@ pub(crate) fn llfn_attrs_from_instance<'ll, 'tcx>(
         to_add.push(MemoryEffects::None.create_attr(cx.llcx));
     }
     if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::NAKED) {
-        to_add.push(AttributeKind::Naked.create_attr(cx.llcx));
-        // HACK(jubilee): "indirect branch tracking" works by attaching prologues to functions.
-        // And it is a module-level attribute, so the alternative is pulling naked functions into
-        // new LLVM modules. Otherwise LLVM's "naked" functions come with endbr prefixes per
-        // https://github.com/rust-lang/rust/issues/98768
-        to_add.push(AttributeKind::NoCfCheck.create_attr(cx.llcx));
-        if llvm_util::get_version() < (19, 0, 0) {
-            // Prior to LLVM 19, branch-target-enforcement was disabled by setting the attribute to
-            // the string "false". Now it is disabled by absence of the attribute.
-            to_add.push(llvm::CreateAttrStringValue(cx.llcx, "branch-target-enforcement", "false"));
-        }
+        // do nothing; a naked function is converted into an extern function
+        // and a global assembly block. LLVM's support for naked functions is
+        // not used.
     } else {
         // Do not set sanitizer attributes for naked functions.
         to_add.extend(sanitize_attrs(cx, codegen_fn_attrs.no_sanitize));

compiler/rustc_codegen_llvm/src/mono_item.rs

@@ -2,6 +2,7 @@ use rustc_codegen_ssa::traits::*;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
 use rustc_middle::bug;
+use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
 use rustc_middle::mir::mono::{Linkage, Visibility};
 use rustc_middle::ty::layout::{FnAbiOf, HasTypingEnv, LayoutOf};
 use rustc_middle::ty::{self, Instance, TypeVisitableExt};
@@ -58,8 +59,15 @@ impl<'tcx> PreDefineCodegenMethods<'tcx> for CodegenCx<'_, 'tcx> {
 
         let fn_abi = self.fn_abi_of_instance(instance, ty::List::empty());
         let lldecl = self.declare_fn(symbol_name, fn_abi, Some(instance));
-        llvm::set_linkage(lldecl, base::linkage_to_llvm(linkage));
         let attrs = self.tcx.codegen_fn_attrs(instance.def_id());
+        let llvm_linkage =
+            if attrs.flags.contains(CodegenFnAttrFlags::NAKED) && linkage == Linkage::Internal {
+                // this is effectively an extern fn, and must have external linkage
+                llvm::Linkage::ExternalLinkage
+            } else {
+                base::linkage_to_llvm(linkage)
+            };
+        llvm::set_linkage(lldecl, llvm_linkage);
         base::set_link_section(lldecl, attrs);
         if (linkage == Linkage::LinkOnceODR || linkage == Linkage::WeakODR)
             && self.tcx.sess.target.supports_comdat()

compiler/rustc_codegen_ssa/src/codegen_attrs.rs

@@ -113,10 +113,7 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
             sym::rustc_allocator_zeroed => {
                 codegen_fn_attrs.flags |= CodegenFnAttrFlags::ALLOCATOR_ZEROED
             }
-            sym::naked => {
-                // this attribute is ignored during codegen, because a function marked as naked is
-                // turned into a global asm block.
-            }
+            sym::naked => codegen_fn_attrs.flags |= CodegenFnAttrFlags::NAKED,
             sym::no_mangle => {
                 if tcx.opt_item_name(did.to_def_id()).is_some() {
                     codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_MANGLE
@@ -545,6 +542,13 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
         }
     });
 
+    // naked function MUST NOT be inlined! This attribute is required for the rust compiler itself,
+    // but not for the code generation backend because at that point the naked function will just be
+    // a declaration, with a definition provided in global assembly.
+    if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::NAKED) {
+        codegen_fn_attrs.inline = InlineAttr::Never;
+    }
+
     codegen_fn_attrs.optimize = attrs.iter().fold(OptimizeAttr::None, |ia, attr| {
         if !attr.has_name(sym::optimize) {
             return ia;
@@ -629,14 +633,6 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
         }
     }
 
-    if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::NAKED) {
-        // naked functions are generated using an extern function and global assembly. To
-        // make sure that these can be linked together by LLVM, the linkage should be external,
-        // unless the user explicitly configured something else (in which case any linker errors
-        // they encounter are their responsibility).
-        codegen_fn_attrs.linkage = codegen_fn_attrs.linkage.or(Some(Linkage::External));
-    }
-
     // Weak lang items have the same semantics as "std internal" symbols in the
     // sense that they're preserved through all our LTO passes and only
     // strippable by the linker.

compiler/rustc_codegen_ssa/src/mir/mod.rs

@@ -177,29 +177,8 @@ pub fn codegen_mir<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
     let fn_abi = cx.fn_abi_of_instance(instance, ty::List::empty());
     debug!("fn_abi: {:?}", fn_abi);
 
-    if cx.tcx().has_attr(instance.def.def_id(), rustc_span::sym::naked) {
-        let cached_llbbs = IndexVec::new();
-
-        let fx: FunctionCx<'_, '_, Bx> = FunctionCx {
-            instance,
-            mir,
-            llfn,
-            fn_abi,
-            cx,
-            personality_slot: None,
-            cached_llbbs,
-            unreachable_block: None,
-            terminate_block: None,
-            cleanup_kinds: None,
-            landing_pads: IndexVec::from_elem(None, &mir.basic_blocks),
-            funclets: IndexVec::from_fn_n(|_| None, mir.basic_blocks.len()),
-            locals: locals::Locals::empty(),
-            debug_context: None,
-            per_local_var_debug_info: None,
-            caller_location: None,
-        };
-
-        fx.codegen_naked_asm(instance);
+    if cx.tcx().codegen_fn_attrs(instance.def_id()).flags.contains(CodegenFnAttrFlags::NAKED) {
+        crate::mir::naked_asm::codegen_naked_asm::<Bx>(cx, &mir, instance);
         return;
     }
 

compiler/rustc_codegen_ssa/src/mir/naked_asm.rs

@@ -1,74 +1,99 @@
-use crate::common;
-use crate::mir::FunctionCx;
-use crate::traits::{AsmMethods, BuilderMethods, GlobalAsmOperandRef};
-use rustc_middle::bug;
-use rustc_middle::mir::InlineAsmOperand;
-use rustc_middle::ty;
-use rustc_middle::ty::layout::{HasTyCtxt, LayoutOf};
+use rustc_attr::InstructionSetAttr;
+use rustc_middle::mir::mono::{MonoItem, MonoItemData, Visibility};
+use rustc_middle::mir::{Body, InlineAsmOperand};
+use rustc_middle::ty::layout::{HasTyCtxt, HasTypingEnv, LayoutOf};
 use rustc_middle::ty::{Instance, TyCtxt};
-
-use rustc_span::sym;
+use rustc_middle::{bug, ty};
 use rustc_target::asm::InlineAsmArch;
 
-impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
-    pub fn codegen_naked_asm(&self, instance: Instance<'tcx>) {
-        let cx = &self.cx;
-
-        let rustc_middle::mir::TerminatorKind::InlineAsm {
-            asm_macro: _,
-            template,
-            ref operands,
-            options,
-            line_spans,
-            targets: _,
-            unwind: _,
-        } = self.mir.basic_blocks.iter().next().unwrap().terminator().kind
-        else {
-            bug!("#[naked] functions should always terminate with an asm! block")
-        };
-
-        let operands: Vec<_> =
-            operands.iter().map(|op| self.inline_to_global_operand(op)).collect();
-
-        let (begin, end) = crate::mir::naked_asm::prefix_and_suffix(cx.tcx(), instance);
-
-        let mut template_vec = Vec::new();
-        template_vec.push(rustc_ast::ast::InlineAsmTemplatePiece::String(begin));
-        template_vec.extend(template.iter().cloned());
-        template_vec.push(rustc_ast::ast::InlineAsmTemplatePiece::String(end));
-
-        cx.codegen_global_asm(&template_vec, &operands, options, line_spans);
-    }
+use crate::common;
+use crate::traits::{AsmCodegenMethods, BuilderMethods, GlobalAsmOperandRef, MiscCodegenMethods};
+
+pub(crate) fn codegen_naked_asm<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
+    cx: &'a Bx::CodegenCx,
+    mir: &Body<'tcx>,
+    instance: Instance<'tcx>,
+) {
+    let rustc_middle::mir::TerminatorKind::InlineAsm {
+        asm_macro: _,
+        template,
+        ref operands,
+        options,
+        line_spans,
+        targets: _,
+        unwind: _,
+    } = mir.basic_blocks.iter().next().unwrap().terminator().kind
+    else {
+        bug!("#[naked] functions should always terminate with an asm! block")
+    };
 
-    fn inline_to_global_operand(&self, op: &InlineAsmOperand<'tcx>) -> GlobalAsmOperandRef<'tcx> {
-        match op {
-            InlineAsmOperand::Const { value } => {
-                let const_value = self.eval_mir_constant(value);
-                let string = common::asm_const_to_str(
-                    self.cx.tcx(),
-                    value.span,
-                    const_value,
-                    self.cx.layout_of(value.ty()),
-                );
-                GlobalAsmOperandRef::Const { string }
-            }
-            InlineAsmOperand::SymFn { value } => {
-                let instance = match value.ty().kind() {
-                    &ty::FnDef(def_id, args) => Instance::new(def_id, args),
-                    _ => bug!("asm sym is not a function"),
-                };
+    let operands: Vec<_> =
+        operands.iter().map(|op| inline_to_global_operand::<Bx>(cx, instance, op)).collect();
 
-                GlobalAsmOperandRef::SymFn { instance }
-            }
-            InlineAsmOperand::SymStatic { def_id } => {
-                GlobalAsmOperandRef::SymStatic { def_id: *def_id }
-            }
-            InlineAsmOperand::In { .. }
-            | InlineAsmOperand::Out { .. }
-            | InlineAsmOperand::InOut { .. }
-            | InlineAsmOperand::Label { .. } => {
-                bug!("invalid operand type for naked_asm!")
-            }
+    let item_data = cx.codegen_unit().items().get(&MonoItem::Fn(instance)).unwrap();
+    let (begin, end) = crate::mir::naked_asm::prefix_and_suffix(cx.tcx(), instance, item_data);
+
+    let mut template_vec = Vec::new();
+    template_vec.push(rustc_ast::ast::InlineAsmTemplatePiece::String(begin.into()));
+    template_vec.extend(template.iter().cloned());
+    template_vec.push(rustc_ast::ast::InlineAsmTemplatePiece::String(end.into()));
+
+    cx.codegen_global_asm(&template_vec, &operands, options, line_spans);
+}
+
+fn inline_to_global_operand<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
+    cx: &'a Bx::CodegenCx,
+    instance: Instance<'tcx>,
+    op: &InlineAsmOperand<'tcx>,
+) -> GlobalAsmOperandRef<'tcx> {
+    match op {
+        InlineAsmOperand::Const { value } => {
+            let const_value = instance
+                .instantiate_mir_and_normalize_erasing_regions(
+                    cx.tcx(),
+                    cx.typing_env(),
+                    ty::EarlyBinder::bind(value.const_),
+                )
+                .eval(cx.tcx(), cx.typing_env(), value.span)
+                .expect("erroneous constant missed by mono item collection");
+
+            let mono_type = instance.instantiate_mir_and_normalize_erasing_regions(
+                cx.tcx(),
+                cx.typing_env(),
+                ty::EarlyBinder::bind(value.ty()),
+            );
+
+            let string = common::asm_const_to_str(
+                cx.tcx(),
+                value.span,
+                const_value,
+                cx.layout_of(mono_type),
+            );
+
+            GlobalAsmOperandRef::Const { string }
+        }
+        InlineAsmOperand::SymFn { value } => {
+            let mono_type = instance.instantiate_mir_and_normalize_erasing_regions(
+                cx.tcx(),
+                cx.typing_env(),
+                ty::EarlyBinder::bind(value.ty()),
+            );
+
+            let instance = match mono_type.kind() {
+                &ty::FnDef(def_id, args) => Instance::new(def_id, args),
+                _ => bug!("asm sym is not a function"),
+            };
+
+            GlobalAsmOperandRef::SymFn { instance }
+        }
+        InlineAsmOperand::SymStatic { def_id } => {
+            GlobalAsmOperandRef::SymStatic { def_id: *def_id }
+        }
+        InlineAsmOperand::In { .. }
+        | InlineAsmOperand::Out { .. }
+        | InlineAsmOperand::InOut { .. }
+        | InlineAsmOperand::Label { .. } => {
+            bug!("invalid operand type for naked_asm!")
         }
     }
 }
@@ -91,7 +116,11 @@ impl AsmBinaryFormat {
     }
 }
 
-fn prefix_and_suffix<'tcx>(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>) -> (String, String) {
+fn prefix_and_suffix<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    instance: Instance<'tcx>,
+    item_data: &MonoItemData,
+) -> (String, String) {
     use std::fmt::Write;
 
     let target = &tcx.sess.target;
@@ -105,24 +134,18 @@ fn prefix_and_suffix<'tcx>(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>) -> (Stri
 
     let asm_name = format!("{}{}", if mangle { "_" } else { "" }, tcx.symbol_name(instance).name);
 
-    let opt_section = tcx
-        .get_attr(instance.def.def_id(), sym::link_section)
-        .and_then(|attr| attr.value_str())
-        .map(|attr| attr.as_str().to_string());
-
-    let instruction_set =
-        tcx.get_attr(instance.def.def_id(), sym::instruction_set).and_then(|attr| attr.value_str());
+    let attrs = tcx.codegen_fn_attrs(instance.def_id());
+    let link_section = attrs.link_section.map(|symbol| symbol.as_str().to_string());
 
     let (arch_prefix, arch_suffix) = if is_arm {
         (
-            match instruction_set {
+            match attrs.instruction_set {
                 None => match is_thumb {
                     true => ".thumb\n.thumb_func",
                     false => ".arm",
                 },
-                Some(sym::a32) => ".arm",
-                Some(sym::t32) => ".thumb\n.thumb_func",
-                Some(other) => bug!("invalid instruction set: {other}"),
+                Some(InstructionSetAttr::ArmA32) => ".arm",
+                Some(InstructionSetAttr::ArmT32) => ".thumb\n.thumb_func",
             },
             match is_thumb {
                 true => ".thumb",
@@ -137,7 +160,7 @@ fn prefix_and_suffix<'tcx>(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>) -> (Stri
     let mut end = String::new();
     match AsmBinaryFormat::from_target(&tcx.sess.target) {
         AsmBinaryFormat::Elf => {
-            let section = opt_section.unwrap_or(format!(".text.{asm_name}"));
+            let section = link_section.unwrap_or(format!(".text.{asm_name}"));
 
             let progbits = match is_arm {
                 true => "%progbits",
@@ -152,11 +175,10 @@ fn prefix_and_suffix<'tcx>(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>) -> (Stri
             writeln!(begin, ".pushsection {section},\"ax\", {progbits}").unwrap();
             writeln!(begin, ".balign 4").unwrap();
             writeln!(begin, ".globl {asm_name}").unwrap();
-            writeln!(begin, ".hidden {asm_name}").unwrap();
-            writeln!(begin, ".type {asm_name}, {function}").unwrap();
-            if let Some(instruction_set) = instruction_set {
-                writeln!(begin, "{}", instruction_set.as_str()).unwrap();
+            if let Visibility::Hidden = item_data.visibility {
+                writeln!(begin, ".hidden {asm_name}").unwrap();
             }
+            writeln!(begin, ".type {asm_name}, {function}").unwrap();
             if !arch_prefix.is_empty() {
                 writeln!(begin, "{}", arch_prefix).unwrap();
             }
@@ -170,13 +192,12 @@ fn prefix_and_suffix<'tcx>(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>) -> (Stri
             }
         }
         AsmBinaryFormat::Macho => {
-            let section = opt_section.unwrap_or("__TEXT,__text".to_string());
+            let section = link_section.unwrap_or("__TEXT,__text".to_string());
             writeln!(begin, ".pushsection {},regular,pure_instructions", section).unwrap();
             writeln!(begin, ".balign 4").unwrap();
             writeln!(begin, ".globl {asm_name}").unwrap();
-            writeln!(begin, ".private_extern {asm_name}").unwrap();
-            if let Some(instruction_set) = instruction_set {
-                writeln!(begin, "{}", instruction_set.as_str()).unwrap();
+            if let Visibility::Hidden = item_data.visibility {
+                writeln!(begin, ".private_extern {asm_name}").unwrap();
             }
             writeln!(begin, "{asm_name}:").unwrap();
 
@@ -187,17 +208,14 @@ fn prefix_and_suffix<'tcx>(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>) -> (Stri
             }
         }
         AsmBinaryFormat::Coff => {
-            let section = opt_section.unwrap_or(format!(".text.{asm_name}"));
+            let section = link_section.unwrap_or(format!(".text.{asm_name}"));
             writeln!(begin, ".pushsection {},\"xr\"", section).unwrap();
             writeln!(begin, ".balign 4").unwrap();
             writeln!(begin, ".globl {asm_name}").unwrap();
             writeln!(begin, ".def {asm_name}").unwrap();
             writeln!(begin, ".scl 2").unwrap();
             writeln!(begin, ".type 32").unwrap();
             writeln!(begin, ".endef {asm_name}").unwrap();
-            if let Some(instruction_set) = instruction_set {
-                writeln!(begin, "{}", instruction_set.as_str()).unwrap();
-            }
             writeln!(begin, "{asm_name}:").unwrap();
 
             writeln!(end).unwrap();