Emit error when trying to use assembler syntax directives in asm!

compiler/rustc_builtin_macros/src/asm.rs

@@ -7,7 +7,10 @@ use rustc_errors::{Applicability, DiagnosticBuilder};
 use rustc_expand::base::{self, *};
 use rustc_parse::parser::Parser;
 use rustc_parse_format as parse;
-use rustc_span::symbol::{kw, sym, Symbol};
+use rustc_span::{
+    symbol::{kw, sym, Symbol},
+    BytePos,
+};
 use rustc_span::{InnerSpan, Span};
 
 struct AsmArgs {
@@ -399,6 +402,8 @@ fn expand_preparsed_asm(ecx: &mut ExtCtxt<'_>, sp: Span, args: AsmArgs) -> P<ast
     let mut line_spans = Vec::with_capacity(args.templates.len());
     let mut curarg = 0;
 
+    let default_dialect = ecx.sess.inline_asm_dialect();
+
     for template_expr in args.templates.into_iter() {
         if !template.is_empty() {
             template.push(ast::InlineAsmTemplatePiece::String("\n".to_string()));
@@ -424,6 +429,60 @@ fn expand_preparsed_asm(ecx: &mut ExtCtxt<'_>, sp: Span, args: AsmArgs) -> P<ast
 
         let template_str = &template_str.as_str();
         let template_snippet = ecx.source_map().span_to_snippet(template_sp).ok();
+
+        if let Some(snippet) = &template_snippet {
+            let snippet = snippet.trim_matches('"');
+            match default_dialect {
+                ast::LlvmAsmDialect::Intel => {
+                    if let Some(span) = check_syntax_directive(snippet, ".intel_syntax") {
+                        let span = template_span.from_inner(span);
+                        let mut err = ecx.struct_span_err(span, "intel syntax is the default syntax on this target, and trying to use this directive may cause issues");
+                        err.span_suggestion(
+                            span,
+                            "remove this assembler directive",
+                            "".to_string(),
+                            Applicability::MachineApplicable,
+                        );
+                        err.emit();
+                    }
+
+                    if let Some(span) = check_syntax_directive(snippet, ".att_syntax") {
+                        let span = template_span.from_inner(span);
+                        let mut err = ecx.struct_span_err(span, "using the .att_syntax directive may cause issues, use the att_syntax option instead");
+                        let asm_end = sp.hi() - BytePos(2);
+                        let suggestions = vec![
+                            (span, "".to_string()),
+                            (
+                                Span::new(asm_end, asm_end, sp.ctxt()),
+                                ", options(att_syntax)".to_string(),
+                            ),
+                        ];
+                        err.multipart_suggestion(
+                        "remove the assembler directive and replace it with options(att_syntax)",
+                        suggestions,
+                        Applicability::MachineApplicable,
+                    );
+                        err.emit();
+                    }
+                }
+                ast::LlvmAsmDialect::Att => {
+                    if let Some(span) = check_syntax_directive(snippet, ".att_syntax") {
+                        let span = template_span.from_inner(span);
+                        let mut err = ecx.struct_span_err(span, "att syntax is the default syntax on this target, and trying to use this directive may cause issues");
+                        err.span_suggestion(
+                            span,
+                            "remove this assembler directive",
+                            "".to_string(),
+                            Applicability::MachineApplicable,
+                        );
+                        err.emit();
+                    }
+
+                    // Use of .intel_syntax is ignored
+                }
+            }
+        }
+
         let mut parser = parse::Parser::new(
             template_str,
             str_style,
@@ -631,3 +690,15 @@ pub fn expand_asm<'cx>(
         }
     }
 }
+
+fn check_syntax_directive<S: AsRef<str>>(piece: S, syntax: &str) -> Option<InnerSpan> {
+    let piece = piece.as_ref();
+    if let Some(idx) = piece.find(syntax) {
+        let end =
+            idx + &piece[idx..].find(|c| matches!(c, '\n' | ';')).unwrap_or(piece[idx..].len());
+        // Offset by one because these represent the span with the " removed
+        Some(InnerSpan::new(idx + 1, end + 1))
+    } else {
+        None
+    }
+}

compiler/rustc_session/src/session.rs

@@ -784,6 +784,13 @@ impl Session {
         }
     }
 
+    pub fn inline_asm_dialect(&self) -> rustc_ast::LlvmAsmDialect {
+        match self.asm_arch {
+            Some(InlineAsmArch::X86 | InlineAsmArch::X86_64) => rustc_ast::LlvmAsmDialect::Intel,
+            _ => rustc_ast::LlvmAsmDialect::Att,
+        }
+    }
+
     pub fn relocation_model(&self) -> RelocModel {
         self.opts.cg.relocation_model.unwrap_or(self.target.relocation_model)
     }

src/test/ui/asm/inline-syntax.arm.stderr

@@ -0,0 +1,14 @@
+error: att syntax is the default syntax on this target, and trying to use this directive may cause issues
+  --> $DIR/inline-syntax.rs:22:15
+   |
+LL |         asm!(".att_syntax noprefix", "nop");
+   |               ^^^^^^^^^^^^^^^^^^^^ help: remove this assembler directive
+
+error: att syntax is the default syntax on this target, and trying to use this directive may cause issues
+  --> $DIR/inline-syntax.rs:25:15
+   |
+LL |         asm!(".att_syntax bbb noprefix", "nop");
+   |               ^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this assembler directive
+
+error: aborting due to 2 previous errors
+

src/test/ui/asm/inline-syntax.rs

@@ -0,0 +1,38 @@
+// revisions: x86_64 arm
+//[x86_64] compile-flags: --target x86_64-unknown-linux-gnu
+//[arm] compile-flags: --target armv7-unknown-linux-gnueabihf
+
+#![feature(no_core, lang_items, rustc_attrs)]
+#![no_core]
+
+#[rustc_builtin_macro]
+macro_rules! asm {
+    () => {};
+}
+
+#[lang = "sized"]
+trait Sized {}
+
+fn main() {
+    unsafe {
+        asm!(".intel_syntax noprefix", "nop");
+        //[x86_64]~^ ERROR intel syntax is the default syntax on this target
+        asm!(".intel_syntax aaa noprefix", "nop");
+        //[x86_64]~^ ERROR intel syntax is the default syntax on this target
+        asm!(".att_syntax noprefix", "nop");
+        //[x86_64]~^ ERROR using the .att_syntax directive may cause issues
+        //[arm]~^^ att syntax is the default syntax on this target
+        asm!(".att_syntax bbb noprefix", "nop");
+        //[x86_64]~^ ERROR using the .att_syntax directive may cause issues
+        //[arm]~^^ att syntax is the default syntax on this target
+        asm!(".intel_syntax noprefix; nop");
+        //[x86_64]~^ ERROR intel syntax is the default syntax on this target
+
+        asm!(
+            r"
+            .intel_syntax noprefix
+            nop"
+        );
+        //[x86_64]~^^^ ERROR intel syntax is the default syntax on this target
+    }
+}

src/test/ui/asm/inline-syntax.x86_64.stderr

@@ -0,0 +1,50 @@
+error: intel syntax is the default syntax on this target, and trying to use this directive may cause issues
+  --> $DIR/inline-syntax.rs:18:15
+   |
+LL |         asm!(".intel_syntax noprefix", "nop");
+   |               ^^^^^^^^^^^^^^^^^^^^^^ help: remove this assembler directive
+
+error: intel syntax is the default syntax on this target, and trying to use this directive may cause issues
+  --> $DIR/inline-syntax.rs:20:15
+   |
+LL |         asm!(".intel_syntax aaa noprefix", "nop");
+   |               ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this assembler directive
+
+error: using the .att_syntax directive may cause issues, use the att_syntax option instead
+  --> $DIR/inline-syntax.rs:22:15
+   |
+LL |         asm!(".att_syntax noprefix", "nop");
+   |               ^^^^^^^^^^^^^^^^^^^^
+   |
+help: remove the assembler directive and replace it with options(att_syntax)
+   |
+LL |         asm!("", "nop", options(att_syntax));
+   |              --       ^^^^^^^^^^^^^^^^^^^^^
+
+error: using the .att_syntax directive may cause issues, use the att_syntax option instead
+  --> $DIR/inline-syntax.rs:25:15
+   |
+LL |         asm!(".att_syntax bbb noprefix", "nop");
+   |               ^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: remove the assembler directive and replace it with options(att_syntax)
+   |
+LL |         asm!("", "nop", options(att_syntax));
+   |              --       ^^^^^^^^^^^^^^^^^^^^^
+
+error: intel syntax is the default syntax on this target, and trying to use this directive may cause issues
+  --> $DIR/inline-syntax.rs:28:15
+   |
+LL |         asm!(".intel_syntax noprefix; nop");
+   |               ^^^^^^^^^^^^^^^^^^^^^^ help: remove this assembler directive
+
+error: intel syntax is the default syntax on this target, and trying to use this directive may cause issues
+  --> $DIR/inline-syntax.rs:33:14
+   |
+LL |               .intel_syntax noprefix
+   |  ______________^
+LL | |             nop"
+   | |_ help: remove this assembler directive
+
+error: aborting due to 6 previous errors
+