Errored when inline asm contans null bytes (#859)

Author: harin-ramesh

src/asm.rs

@@ -12,13 +12,13 @@ use rustc_codegen_ssa::traits::{
 };
 use rustc_middle::bug;
 use rustc_middle::ty::Instance;
-use rustc_span::Span;
+use rustc_span::{DUMMY_SP, Span};
 use rustc_target::asm::*;
 
 use crate::builder::Builder;
 use crate::callee::get_fn;
 use crate::context::CodegenCx;
-use crate::errors::UnwindingInlineAsm;
+use crate::errors::{NulBytesInAsm, UnwindingInlineAsm};
 use crate::type_of::LayoutGccExt;
 
 // Rust asm! and GCC Extended Asm semantics differ substantially.
@@ -530,8 +530,15 @@ impl<'a, 'gcc, 'tcx> AsmBuilderMethods<'tcx> for Builder<'a, 'gcc, 'tcx> {
             template_str.push_str(INTEL_SYNTAX_INS);
         }
 
-        // 4. Generate Extended Asm block
+        // NOTE: GCC's extended asm uses CString which cannot contain nul bytes.
+        // Emit an error if there are any nul bytes in the template string.
+        if template_str.contains('\0') {
+            let err_sp = span.first().copied().unwrap_or(DUMMY_SP);
+            self.sess().dcx().emit_err(NulBytesInAsm { span: err_sp });
+            return;
+        }
 
+        // 4. Generate Extended Asm block
         let block = self.llbb();
         let extended_asm = if let Some(dest) = dest {
             assert!(!labels.is_empty());
@@ -859,7 +866,7 @@ impl<'gcc, 'tcx> AsmCodegenMethods<'tcx> for CodegenCx<'gcc, 'tcx> {
         template: &[InlineAsmTemplatePiece],
         operands: &[GlobalAsmOperandRef<'tcx>],
         options: InlineAsmOptions,
-        _line_spans: &[Span],
+        line_spans: &[Span],
     ) {
         let asm_arch = self.tcx.sess.asm_arch.unwrap();
 
@@ -926,6 +933,13 @@ impl<'gcc, 'tcx> AsmCodegenMethods<'tcx> for CodegenCx<'gcc, 'tcx> {
         }
         // NOTE: seems like gcc will put the asm in the wrong section, so set it to .text manually.
         template_str.push_str("\n.popsection");
+        // NOTE: GCC's add_top_level_asm uses CString which cannot contain nul bytes.
+        // Emit an error if there are any nul bytes in the template string.
+        if template_str.contains('\0') {
+            let span = line_spans.first().copied().unwrap_or(DUMMY_SP);
+            self.tcx.dcx().emit_err(NulBytesInAsm { span });
+            return;
+        }
         self.context.add_top_level_asm(None, &template_str);
     }
 

src/errors.rs

@@ -23,3 +23,10 @@ pub(crate) struct LtoBitcodeFromRlib {
 #[derive(Diagnostic)]
 #[diag("explicit tail calls with the 'become' keyword are not implemented in the GCC backend")]
 pub(crate) struct ExplicitTailCallsUnsupported;
+
+#[derive(Diagnostic)]
+#[diag("asm contains a NUL byte")]
+pub(crate) struct NulBytesInAsm {
+    #[primary_span]
+    pub span: Span,
+}

tests/compile/asm_nul_byte.rs

@@ -0,0 +1,15 @@
+// Compiler:
+//   status: error
+//   stderr:
+//     error: asm contains a NUL byte
+//     ...
+
+// Test that inline asm containing a NUL byte emits an error.
+
+use std::arch::asm;
+
+fn main() {
+    unsafe {
+        asm!("\0");
+    }
+}

tests/compile/global_asm_nul_byte.rs

@@ -0,0 +1,13 @@
+// Compiler:
+//   status: error
+//   stderr:
+//     error: asm contains a NUL byte
+//     ...
+
+// Test that global_asm containing a NUL byte emits an error.
+
+#![crate_type = "lib"]
+
+use std::arch::global_asm;
+
+global_asm!("\0");

tests/compile/naked_asm_nul_byte.rs

@@ -0,0 +1,17 @@
+// Compiler:
+//   status: error
+//   stderr:
+//     ...
+//     error: asm contains a NUL byte
+//     ...
+
+// Test that naked_asm containing a NUL byte emits an error.
+
+#![crate_type = "lib"]
+
+use std::arch::naked_asm;
+
+#[unsafe(naked)]
+pub extern "C" fn nul_byte_naked() {
+    naked_asm!("\0")
+}

tests/lang_tests.rs

@@ -201,7 +201,7 @@ fn compile_tests(tempdir: PathBuf, current_dir: String) {
         "lang compile",
         "tests/compile",
         TestMode::Compile,
-        &["simd-ffi.rs"],
+        &["simd-ffi.rs", "asm_nul_byte.rs", "global_asm_nul_byte.rs", "naked_asm_nul_byte.rs"],
     );
 }