[PATCH] Add support for DW_AT_main_subprogram

Mon Nov 28 10:07:14 PST 2016

Looks good to me, please commit.

(test might do with an improvement - to make sure the attribute is
appearing in the right place, I'd expect something like:

CHECK: DW_TAG_subprogram
CHECK-NOT: {{DW_TAG|NULL}}
CHECK:   DW_AT_name {{.*}} "main"
CHECK-NOT: {{DW_TAG|NULL}}
CHECK:   DW_AT_main_subprogram...

or the like.

On Tue, Nov 22, 2016 at 11:22 PM Tom Tromey via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> I'd like the Rust compiler to emit DW_AT_main_subprogram in its DWARF
> output, so that debuggers can find the user-provided main entry point.
> See https://github.com/rust-lang/rust/issues/32620
>
> This patch adds support for DW_AT_main_subprogram to LLVM to support
> this effort.
>
> I've built and tested it on x86-64 Fedora 24.
>
> Note that while DWARF allows DW_AT_main_subprogram to appear on a
> DW_TAG_compile_unit DIE, I did not need this, so I've only implemented
> it for DW_TAG_subroutine.
>
> I've added a new test case, which I copied from version.ll and then
> modified to suit.
>
> Tom
> ---
>  include/llvm/IR/DebugInfoFlags.def       |  3 ++-
>  include/llvm/IR/DebugInfoMetadata.h      |  1 +
>  lib/CodeGen/AsmPrinter/DwarfUnit.cpp     |  3 +++
>  test/DebugInfo/Generic/mainsubprogram.ll | 31
> +++++++++++++++++++++++++++++++
>  4 files changed, 37 insertions(+), 1 deletion(-)
>  create mode 100644 test/DebugInfo/Generic/mainsubprogram.ll
>
> diff --git a/include/llvm/IR/DebugInfoFlags.def
> b/include/llvm/IR/DebugInfoFlags.def
> index 013114c..87f3dc9 100644
> --- a/include/llvm/IR/DebugInfoFlags.def
> +++ b/include/llvm/IR/DebugInfoFlags.def
> @@ -41,6 +41,7 @@ HANDLE_DI_FLAG((3 << 16), VirtualInheritance)
>  HANDLE_DI_FLAG((1 << 18), IntroducedVirtual)
>  HANDLE_DI_FLAG((1 << 19), BitField)
>  HANDLE_DI_FLAG((1 << 20), NoReturn)
> +HANDLE_DI_FLAG((1 << 21), MainSubprogram)
>
>  // To avoid needing a dedicated value for IndirectVirtualBase, we use
>  // the bitwise or of Virtual and FwdDecl, which does not otherwise
> @@ -50,7 +51,7 @@ HANDLE_DI_FLAG((1 << 2) | (1 << 5), IndirectVirtualBase)
>  #ifdef DI_FLAG_LARGEST_NEEDED
>  // intended to be used with ADT/BitmaskEnum.h
>  // NOTE: always must be equal to largest flag, check this when adding new
> flag
> -HANDLE_DI_FLAG((1 << 20), Largest)
> +HANDLE_DI_FLAG((1 << 21), Largest)
>  #undef DI_FLAG_LARGEST_NEEDED
>  #endif
>
> diff --git a/include/llvm/IR/DebugInfoMetadata.h
> b/include/llvm/IR/DebugInfoMetadata.h
> index aaa0e0d..fcd4d08 100644
> --- a/include/llvm/IR/DebugInfoMetadata.h
> +++ b/include/llvm/IR/DebugInfoMetadata.h
> @@ -1420,6 +1420,7 @@ public:
>    }
>    bool isExplicit() const { return getFlags() & FlagExplicit; }
>    bool isPrototyped() const { return getFlags() & FlagPrototyped; }
> +  bool isMainSubprogram() const { return getFlags() & FlagMainSubprogram;
> }
>
>    /// Check if this is reference-qualified.
>    ///
> diff --git a/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
> b/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
> index a49518a..d2fbf0a 100644
> --- a/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
> +++ b/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
> @@ -1282,6 +1282,9 @@ void DwarfUnit::applySubprogramAttributes(const
> DISubprogram *SP, DIE &SPDie,
>
>    if (SP->isExplicit())
>      addFlag(SPDie, dwarf::DW_AT_explicit);
> +
> +  if (SP->isMainSubprogram())
> +    addFlag(SPDie, dwarf::DW_AT_main_subprogram);
>  }
>
>  void DwarfUnit::constructSubrangeDIE(DIE &Buffer, const DISubrange *SR,
> diff --git a/test/DebugInfo/Generic/mainsubprogram.ll
> b/test/DebugInfo/Generic/mainsubprogram.ll
> new file mode 100644
> index 0000000..be843c4
> --- /dev/null
> +++ b/test/DebugInfo/Generic/mainsubprogram.ll
> @@ -0,0 +1,31 @@
> +; REQUIRES: object-emission
> +
> +; RUN: %llc_dwarf -O0 -filetype=obj < %s > %t
> +; RUN: llvm-dwarfdump %t | FileCheck %s
> +
> +; Make sure we're emitting DW_AT_main_subprogram.
> +; CHECK:   DW_AT_main_subprogram [DW_FORM_flag_present] (true)
> +
> +define i32 @main() #0 !dbg !4 {
> +entry:
> +  %retval = alloca i32, align 4
> +  store i32 0, i32* %retval
> +  ret i32 0, !dbg !10
> +}
> +
> +attributes #0 = { nounwind uwtable "less-precise-fpmad"="false"
> "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf"
> "no-infs-fp-math"="false" "no-nans-fp-math"="false"
> "unsafe-fp-math"="false" "use-soft-float"="false" }
> +
> +!llvm.dbg.cu = !{!0}
> +!llvm.module.flags = !{!9, !11}
> +
> +!0 = distinct !DICompileUnit(language: DW_LANG_C99, producer: "clang
> version 3.4 (trunk 185475)", isOptimized: false, emissionKind: FullDebug,
> file: !1, enums: !2, retainedTypes: !2, globals: !2, imports: !2)
> +!1 = !DIFile(filename: "CodeGen/dwarf-version.c", directory: "test")
> +!2 = !{}
> +!4 = distinct !DISubprogram(name: "main", line: 6, isLocal: false,
> isDefinition: true, virtualIndex: 6, flags: DIFlagPrototyped |
> DIFlagMainSubprogram, isOptimized: false, unit: !0, scopeLine: 6, file: !1,
> scope: !5, type: !6, variables: !2)
> +!5 = !DIFile(filename: "CodeGen/dwarf-version.c", directory: "test")
> +!6 = !DISubroutineType(types: !7)
> +!7 = !{!8}
> +!8 = !DIBasicType(tag: DW_TAG_base_type, name: "int", size: 32, align:
> 32, encoding: DW_ATE_signed)
> +!9 = !{i32 2, !"Dwarf Version", i32 4}
> +!10 = !DILocation(line: 7, scope: !4)
> +!11 = !{i32 1, !"Debug Info Version", i32 3}
> --
> 2.7.4
>
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