[PATCH] D153484: Do not emit a named symbol to denote the start of the __debug_frame section

[Shubham Sandeep Rastogi via Phabricator via llvm-commits]

rastogishubham created this revision.
rastogishubham added reviewers: friss, aprantl.
rastogishubham added a project: debug-info.
Herald added subscribers: ormris, hiraditya, kristof.beyls.
Herald added a project: All.
rastogishubham requested review of this revision.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.

When emitting a debug_frame section, we can see that it contains a named symbol.

  echo "void foo(void) {}" | clang -arch arm64  -ffreestanding -g -c -o /tmp/test.o -x c - 
  nm /tmp/test.o -s __DWARF __debug_frame
  0000000000000200 s ltmp1

There are no such symbols emitted in any of the other DWARF sections, this is because when the __debug_frame section is created, it doesn't get a `BeginSymName` and so it creates a named symbol, such as `ltmp1` and emits it when we switch to the section in MCDwarf.cpp

This patch fixes the above issue


https://reviews.llvm.org/D153484

Files:
  llvm/lib/MC/MCObjectFileInfo.cpp
  llvm/test/DebugInfo/debug_frame_symbol.ll


Index: llvm/test/DebugInfo/debug_frame_symbol.ll
===================================================================
--- /dev/null
+++ llvm/test/DebugInfo/debug_frame_symbol.ll
@@ -0,0 +1,42 @@
+; This test makes sure that the debug_frame section does not contain any named symbols.
+; The ll file was compiled by using the following command.
+; > clang -arch arm64 -ffreestanding -g -c -x c -o /tmp/test.o /tmp/test.c
+;
+; > cat /tmp/test.c
+; void foo(void) {}
+
+
+; RUN: llc %s -O0 -filetype=obj -o - | llvm-nm -s __DWARF __debug_frame - | FileCheck %s --allow-empty
+
+; CHECK-NOT: {{.*}}ltmp{{[0-9]+}}
+
+; ModuleID = '/tmp/test.c'
+source_filename = "/tmp/test.c"
+target datalayout = "e-m:o-i64:64-i128:128-n32:64-S128"
+target triple = "arm64-apple-macosx14.0.0"
+
+; Function Attrs: noinline nounwind optnone ssp
+define void @foo() #0 !dbg !8 {
+entry:
+  ret void, !dbg !12
+}
+
+attributes #0 = { noinline nounwind optnone ssp "frame-pointer"="non-leaf" "no-builtins" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="apple-m1" "target-features"="+aes,+crc,+dotprod,+fp-armv8,+fp16fml,+fullfp16,+lse,+neon,+ras,+rcpc,+rdm,+sha2,+sha3,+v8.1a,+v8.2a,+v8.3a,+v8.4a,+v8.5a,+v8a,+zcm,+zcz" }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2, !3, !4, !5, !6}
+!llvm.ident = !{!7}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C11, file: !1, producer: "clang version 17.0.0 (git at github.com:llvm/llvm-project.git e734a12b608f8c4a2b03fb2f3194de1cc3b43344)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: Apple, sysroot: "/")
+!1 = !DIFile(filename: "/tmp/test.c", directory: "/Users/shubham/Development/llvm-project/llvm/test/DebugInfo")
+!2 = !{i32 7, !"Dwarf Version", i32 4}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = !{i32 1, !"wchar_size", i32 4}
+!5 = !{i32 8, !"PIC Level", i32 2}
+!6 = !{i32 7, !"frame-pointer", i32 1}
+!7 = !{!"clang version 17.0.0 (git at github.com:llvm/llvm-project.git e734a12b608f8c4a2b03fb2f3194de1cc3b43344)"}
+!8 = distinct !DISubprogram(name: "foo", scope: !9, file: !9, line: 1, type: !10, scopeLine: 1, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0)
+!9 = !DIFile(filename: "/tmp/test.c", directory: "")
+!10 = !DISubroutineType(types: !11)
+!11 = !{null}
+!12 = !DILocation(line: 1, column: 17, scope: !8)
Index: llvm/lib/MC/MCObjectFileInfo.cpp
===================================================================
--- llvm/lib/MC/MCObjectFileInfo.cpp
+++ llvm/lib/MC/MCObjectFileInfo.cpp
@@ -249,7 +249,7 @@
                            SectionKind::getMetadata(), "section_line_str");
   DwarfFrameSection =
       Ctx->getMachOSection("__DWARF", "__debug_frame", MachO::S_ATTR_DEBUG,
-                           SectionKind::getMetadata());
+                           SectionKind::getMetadata(), "section_frame");
   DwarfPubNamesSection =
       Ctx->getMachOSection("__DWARF", "__debug_pubnames", MachO::S_ATTR_DEBUG,
                            SectionKind::getMetadata());


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D153484.533437.patch
Type: text/x-patch
Size: 3035 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20230621/e709d56a/attachment.bin>