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carbon-lang/toolchain/lower/testdata/interop/cpp/extern_c.carbon
T
David BlaikieandDana Jansens a179bd461b Start plumbing through debug info type information with function parameters/return value (#6410) 
This adds just enough debug info for i32/int parameters and return
values, with a path forward for adding DWARF type metadata for other
types.

As it happens, return type information is carried separately from
parameter information:
* Return type information is carried in the `type` of the `DISubprogram`
  (as a `DISubroutineType` - which does carry parameter type information
  as well, but that's unused when the DWARF is emitted by LLVM)
* Parameter information is carried by `DILocalVariable`s with a non-zero
  `arg` value (representing the order of function parameters)

In the absence of locations for the parameters (future work), nothing
would usually keep the `DILocalVariable` live/reachable when emitting
DWARF - so for cases where this can happen (for clang, this happens in
optimized builds where all references to the parameter variable might be
optimized away) the variables can be "retained" in a list on the
`DISubprogram` - achieved by passing `AlwaysPreserve` parameter to
`createParameterVariable` (adds them to a list, then that list gets
attached to the `DISubprogram` when it's finalized later)

For now, any unsupported types are emitted as `void*` (except void
return, which is implemented as void) as a placeholder.

Given this example:
```
import Core library "io";
class MyClass {
}
fn Unsupported(v: MyClass) {
}
fn Ret() -> i32 {
  return 42;
}
fn Arg(x: i32) {
  Core.Print(x);
}
fn Run() {
}
```
this is the resulting DWARF:
```
DW_TAG_compile_unit
  DW_AT_name    ("test.carbon")
  DW_TAG_subprogram
    DW_AT_name  ("Unsupported")
    DW_TAG_formal_parameter
      DW_AT_type        (0x00000066 "void *")
  DW_TAG_subprogram
    DW_AT_name  ("Ret")
    DW_AT_type  (0x00000062 "int")
  DW_TAG_subprogram
    DW_AT_name  ("Arg")
    DW_TAG_formal_parameter
      DW_AT_type        (0x00000062 "int")
  DW_TAG_subprogram
    DW_AT_name  ("Run")
  DW_TAG_base_type
    DW_AT_name  ("int")
  DW_TAG_pointer_type
```
And the debugger:
```
(gdb) p Ret()
$1 = 42
(gdb) p Arg(4)
4
$2 = void
```

I'm not sure if there's a way this logic should be merged with the logic
for making the `llvm::Function` type (which the `DISubroutineType`
building code was inspired by/copied from) - since they're done at
different times/places, I don't think there's an easy way to do it in
one pass, but maybe the code can be shared (even if it's run twice) in
some generic `SemIR::Function` type walker.

---------

Co-authored-by: Dana Jansens <danakj@orodu.net>
2025-11-25 23:25:09 +00:00

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// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
// Exceptions. See /LICENSE for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
// INCLUDE-FILE: toolchain/testing/testdata/min_prelude/int.carbon
//
// AUTOUPDATE
// TIP: To test this file alone, run:
// TIP: bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/lower/testdata/interop/cpp/extern_c.carbon
// TIP: To dump output, run:
// TIP: bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/extern_c.carbon
// ============================================================================
// extern "C" function
// ============================================================================
// --- extern_c_function.h
extern "C" void foo();
// --- import_extern_c_function.carbon
library "[[@TEST_NAME]]";
import Cpp library "extern_c_function.h";
fn MyF() {
Cpp.foo();
}
// ============================================================================
// Overload set of extern "C" function and a C++ function
// ============================================================================
// --- extern_c_function_with_cpp_overload_set.carbon
library "[[@TEST_NAME]]";
import Cpp inline '''
extern "C" void foo();
void foo(int x);
''';
fn MyF() {
Cpp.foo();
Cpp.foo(5);
}
// ============================================================================
// extern "C" variable
// ============================================================================
// --- extern_c_variable.h
extern "C" int foo;
// --- import_extern_c_variable.carbon
library "[[@TEST_NAME]]";
import Cpp library "extern_c_variable.h";
fn MyF() -> i32 {
return Cpp.foo;
}
// ============================================================================
// extern "C" function with C++ special name
// ============================================================================
// --- extern_c_with_special_name.h
struct X {};
extern "C" X operator+(X, X);
// --- import_extern_c_with_special_name.carbon
library "[[@TEST_NAME]]";
import Cpp library "extern_c_with_special_name.h";
fn MyF(a: Cpp.X, b: Cpp.X) -> Cpp.X {
return a + b;
}
// ============================================================================
// extern "C" function with asm label
// ============================================================================
// --- extern_c_with_asm_label.h
extern "C" void foo() __asm__("bar");
// --- import_extern_c_with_asm_label.carbon
library "[[@TEST_NAME]]";
import Cpp library "extern_c_with_asm_label.h";
fn MyF() {
Cpp.foo();
}
// CHECK:STDOUT: ; ModuleID = 'import_extern_c_function.carbon'
// CHECK:STDOUT: source_filename = "import_extern_c_function.carbon"
// CHECK:STDOUT: target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
// CHECK:STDOUT: target triple = "x86_64-unknown-linux-gnu"
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: nounwind
// CHECK:STDOUT: define void @_CMyF.Main() #0 !dbg !7 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: call void @foo(), !dbg !10
// CHECK:STDOUT: ret void, !dbg !11
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: declare void @foo()
// CHECK:STDOUT:
// CHECK:STDOUT: attributes #0 = { nounwind }
// CHECK:STDOUT:
// CHECK:STDOUT: !llvm.module.flags = !{!0, !1, !2, !3, !4}
// CHECK:STDOUT: !llvm.dbg.cu = !{!5}
// CHECK:STDOUT:
// CHECK:STDOUT: !0 = !{i32 7, !"Dwarf Version", i32 5}
// CHECK:STDOUT: !1 = !{i32 2, !"Debug Info Version", i32 3}
// CHECK:STDOUT: !2 = !{i32 1, !"wchar_size", i32 4}
// CHECK:STDOUT: !3 = !{i32 8, !"PIC Level", i32 0}
// CHECK:STDOUT: !4 = !{i32 7, !"PIE Level", i32 2}
// CHECK:STDOUT: !5 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !6, producer: "carbon", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug)
// CHECK:STDOUT: !6 = !DIFile(filename: "import_extern_c_function.carbon", directory: "")
// CHECK:STDOUT: !7 = distinct !DISubprogram(name: "MyF", linkageName: "_CMyF.Main", scope: null, file: !6, line: 6, type: !8, spFlags: DISPFlagDefinition, unit: !5)
// CHECK:STDOUT: !8 = !DISubroutineType(types: !9)
// CHECK:STDOUT: !9 = !{null}
// CHECK:STDOUT: !10 = !DILocation(line: 7, column: 3, scope: !7)
// CHECK:STDOUT: !11 = !DILocation(line: 6, column: 1, scope: !7)
// CHECK:STDOUT: ; ModuleID = 'extern_c_function_with_cpp_overload_set.carbon'
// CHECK:STDOUT: source_filename = "extern_c_function_with_cpp_overload_set.carbon"
// CHECK:STDOUT: target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
// CHECK:STDOUT: target triple = "x86_64-unknown-linux-gnu"
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: nounwind
// CHECK:STDOUT: define void @_CMyF.Main() #0 !dbg !7 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: call void @foo(), !dbg !10
// CHECK:STDOUT: call void @_Z3fooi(i32 5), !dbg !11
// CHECK:STDOUT: ret void, !dbg !12
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: declare void @foo()
// CHECK:STDOUT:
// CHECK:STDOUT: declare void @_Z3fooi(i32)
// CHECK:STDOUT:
// CHECK:STDOUT: attributes #0 = { nounwind }
// CHECK:STDOUT:
// CHECK:STDOUT: !llvm.module.flags = !{!0, !1, !2, !3, !4}
// CHECK:STDOUT: !llvm.dbg.cu = !{!5}
// CHECK:STDOUT:
// CHECK:STDOUT: !0 = !{i32 7, !"Dwarf Version", i32 5}
// CHECK:STDOUT: !1 = !{i32 2, !"Debug Info Version", i32 3}
// CHECK:STDOUT: !2 = !{i32 1, !"wchar_size", i32 4}
// CHECK:STDOUT: !3 = !{i32 8, !"PIC Level", i32 0}
// CHECK:STDOUT: !4 = !{i32 7, !"PIE Level", i32 2}
// CHECK:STDOUT: !5 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !6, producer: "carbon", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug)
// CHECK:STDOUT: !6 = !DIFile(filename: "extern_c_function_with_cpp_overload_set.carbon", directory: "")
// CHECK:STDOUT: !7 = distinct !DISubprogram(name: "MyF", linkageName: "_CMyF.Main", scope: null, file: !6, line: 9, type: !8, spFlags: DISPFlagDefinition, unit: !5)
// CHECK:STDOUT: !8 = !DISubroutineType(types: !9)
// CHECK:STDOUT: !9 = !{null}
// CHECK:STDOUT: !10 = !DILocation(line: 10, column: 3, scope: !7)
// CHECK:STDOUT: !11 = !DILocation(line: 11, column: 3, scope: !7)
// CHECK:STDOUT: !12 = !DILocation(line: 9, column: 1, scope: !7)
// CHECK:STDOUT: ; ModuleID = 'import_extern_c_variable.carbon'
// CHECK:STDOUT: source_filename = "import_extern_c_variable.carbon"
// CHECK:STDOUT: target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
// CHECK:STDOUT: target triple = "x86_64-unknown-linux-gnu"
// CHECK:STDOUT:
// CHECK:STDOUT: @foo = external global i32
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: nounwind
// CHECK:STDOUT: define i32 @_CMyF.Main() #0 !dbg !7 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: %.loc7 = load i32, ptr @foo, align 4, !dbg !11
// CHECK:STDOUT: ret i32 %.loc7, !dbg !12
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: attributes #0 = { nounwind }
// CHECK:STDOUT:
// CHECK:STDOUT: !llvm.module.flags = !{!0, !1, !2, !3, !4}
// CHECK:STDOUT: !llvm.dbg.cu = !{!5}
// CHECK:STDOUT:
// CHECK:STDOUT: !0 = !{i32 7, !"Dwarf Version", i32 5}
// CHECK:STDOUT: !1 = !{i32 2, !"Debug Info Version", i32 3}
// CHECK:STDOUT: !2 = !{i32 1, !"wchar_size", i32 4}
// CHECK:STDOUT: !3 = !{i32 8, !"PIC Level", i32 0}
// CHECK:STDOUT: !4 = !{i32 7, !"PIE Level", i32 2}
// CHECK:STDOUT: !5 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !6, producer: "carbon", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug)
// CHECK:STDOUT: !6 = !DIFile(filename: "import_extern_c_variable.carbon", directory: "")
// CHECK:STDOUT: !7 = distinct !DISubprogram(name: "MyF", linkageName: "_CMyF.Main", scope: null, file: !6, line: 6, type: !8, spFlags: DISPFlagDefinition, unit: !5)
// CHECK:STDOUT: !8 = !DISubroutineType(types: !9)
// CHECK:STDOUT: !9 = !{!10}
// CHECK:STDOUT: !10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
// CHECK:STDOUT: !11 = !DILocation(line: 7, column: 10, scope: !7)
// CHECK:STDOUT: !12 = !DILocation(line: 7, column: 3, scope: !7)
// CHECK:STDOUT: ; ModuleID = 'import_extern_c_with_special_name.carbon'
// CHECK:STDOUT: source_filename = "import_extern_c_with_special_name.carbon"
// CHECK:STDOUT: target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
// CHECK:STDOUT: target triple = "x86_64-unknown-linux-gnu"
// CHECK:STDOUT:
// CHECK:STDOUT: %struct.X = type { i8 }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: nounwind
// CHECK:STDOUT: define void @_CMyF.Main(ptr sret({}) %return, ptr %a, ptr %b) #0 !dbg !7 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: call void @_Zpl1XS_.carbon_thunk(ptr %a, ptr %b, ptr %return), !dbg !14
// CHECK:STDOUT: ret void, !dbg !15
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: alwaysinline mustprogress
// CHECK:STDOUT: define dso_local void @_Zpl1XS_.carbon_thunk(ptr %0, ptr %1, ptr %return) #1 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: %.addr = alloca ptr, align 8
// CHECK:STDOUT: %.addr1 = alloca ptr, align 8
// CHECK:STDOUT: %return.addr = alloca ptr, align 8
// CHECK:STDOUT: %agg.tmp = alloca %struct.X, align 1
// CHECK:STDOUT: %agg.tmp2 = alloca %struct.X, align 1
// CHECK:STDOUT: %undef.agg.tmp = alloca %struct.X, align 1
// CHECK:STDOUT: store ptr %0, ptr %.addr, align 8
// CHECK:STDOUT: store ptr %1, ptr %.addr1, align 8
// CHECK:STDOUT: store ptr %return, ptr %return.addr, align 8
// CHECK:STDOUT: %2 = load ptr, ptr %return.addr, align 8
// CHECK:STDOUT: %3 = load ptr, ptr %.addr, align 8
// CHECK:STDOUT: %4 = load ptr, ptr %.addr1, align 8
// CHECK:STDOUT: call void @_Zpl1XS_()
// CHECK:STDOUT: ret void
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: declare void @_Zpl1XS_() #2
// CHECK:STDOUT:
// CHECK:STDOUT: attributes #0 = { nounwind }
// CHECK:STDOUT: attributes #1 = { alwaysinline mustprogress "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="0" "target-cpu"="x86-64" "target-features"="+cmov,+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" }
// CHECK:STDOUT: attributes #2 = { "no-trapping-math"="true" "stack-protector-buffer-size"="0" "target-cpu"="x86-64" "target-features"="+cmov,+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" }
// CHECK:STDOUT:
// CHECK:STDOUT: !llvm.module.flags = !{!0, !1, !2, !3, !4}
// CHECK:STDOUT: !llvm.dbg.cu = !{!5}
// CHECK:STDOUT:
// CHECK:STDOUT: !0 = !{i32 7, !"Dwarf Version", i32 5}
// CHECK:STDOUT: !1 = !{i32 2, !"Debug Info Version", i32 3}
// CHECK:STDOUT: !2 = !{i32 1, !"wchar_size", i32 4}
// CHECK:STDOUT: !3 = !{i32 8, !"PIC Level", i32 0}
// CHECK:STDOUT: !4 = !{i32 7, !"PIE Level", i32 2}
// CHECK:STDOUT: !5 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !6, producer: "carbon", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug)
// CHECK:STDOUT: !6 = !DIFile(filename: "import_extern_c_with_special_name.carbon", directory: "")
// CHECK:STDOUT: !7 = distinct !DISubprogram(name: "MyF", linkageName: "_CMyF.Main", scope: null, file: !6, line: 6, type: !8, spFlags: DISPFlagDefinition, unit: !5, retainedNodes: !11)
// CHECK:STDOUT: !8 = !DISubroutineType(types: !9)
// CHECK:STDOUT: !9 = !{!10, !10, !10}
// CHECK:STDOUT: !10 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: null, size: 8)
// CHECK:STDOUT: !11 = !{!12, !13}
// CHECK:STDOUT: !12 = !DILocalVariable(arg: 1, scope: !7, type: !10)
// CHECK:STDOUT: !13 = !DILocalVariable(arg: 2, scope: !7, type: !10)
// CHECK:STDOUT: !14 = !DILocation(line: 7, column: 10, scope: !7)
// CHECK:STDOUT: !15 = !DILocation(line: 7, column: 3, scope: !7)
// CHECK:STDOUT: ; ModuleID = 'import_extern_c_with_asm_label.carbon'
// CHECK:STDOUT: source_filename = "import_extern_c_with_asm_label.carbon"
// CHECK:STDOUT: target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
// CHECK:STDOUT: target triple = "x86_64-unknown-linux-gnu"
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: nounwind
// CHECK:STDOUT: define void @_CMyF.Main() #0 !dbg !7 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: call void @bar(), !dbg !10
// CHECK:STDOUT: ret void, !dbg !11
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: declare void @bar()
// CHECK:STDOUT:
// CHECK:STDOUT: attributes #0 = { nounwind }
// CHECK:STDOUT:
// CHECK:STDOUT: !llvm.module.flags = !{!0, !1, !2, !3, !4}
// CHECK:STDOUT: !llvm.dbg.cu = !{!5}
// CHECK:STDOUT:
// CHECK:STDOUT: !0 = !{i32 7, !"Dwarf Version", i32 5}
// CHECK:STDOUT: !1 = !{i32 2, !"Debug Info Version", i32 3}
// CHECK:STDOUT: !2 = !{i32 1, !"wchar_size", i32 4}
// CHECK:STDOUT: !3 = !{i32 8, !"PIC Level", i32 0}
// CHECK:STDOUT: !4 = !{i32 7, !"PIE Level", i32 2}
// CHECK:STDOUT: !5 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !6, producer: "carbon", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug)
// CHECK:STDOUT: !6 = !DIFile(filename: "import_extern_c_with_asm_label.carbon", directory: "")
// CHECK:STDOUT: !7 = distinct !DISubprogram(name: "MyF", linkageName: "_CMyF.Main", scope: null, file: !6, line: 6, type: !8, spFlags: DISPFlagDefinition, unit: !5)
// CHECK:STDOUT: !8 = !DISubroutineType(types: !9)
// CHECK:STDOUT: !9 = !{null}
// CHECK:STDOUT: !10 = !DILocation(line: 7, column: 3, scope: !7)
// CHECK:STDOUT: !11 = !DILocation(line: 6, column: 1, scope: !7)
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