[BPF] add "llvm." prefix to BPF internally created globals

Currently, BPF backend creates some global variables with name like
  <type_name>:<reloc_type>:<patch_imm>$<access_str>
to carry certain information to BPF backend.

With direct clang compilation, the following code in
   llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
is triggered and the above globals are emitted to the ELF file.
(clang enabled this as opt flag -faddrsig is on by default.)
   if (TM.Options.EmitAddrsig) {
    // Emit address-significance attributes for all globals.
    OutStreamer->EmitAddrsig();
    for (const GlobalValue &GV : M.global_values())
      if (!GV.use_empty() && !GV.isThreadLocal() &&
          !GV.hasDLLImportStorageClass() && !GV.getName().startswith("llvm.") &&
          !GV.hasAtLeastLocalUnnamedAddr())
        OutStreamer->EmitAddrsigSym(getSymbol(&GV));
  }
...
 10162: 0000000000000000     0 NOTYPE  GLOBAL DEFAULT   UND tcp_sock:0:2048$0:117
 10163: 0000000000000000     0 NOTYPE  GLOBAL DEFAULT   UND tcp_sock:0:2112$0:126:0
 10164: 0000000000000000     0 NOTYPE  GLOBAL DEFAULT   UND tcp_sock:1:8$0:31:6
...
While in llc, those globals are not emited since EmitAddrsig
default option is false for llc. The llc flag "-addrsig" can be used to
enable the above code.

This patch added "llvm." prefix to these internal globals so that
they can be ignored in the above codes and possible other
places.

Differential Revision: https://reviews.llvm.org/D70703

1 files changed, 65 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/BPF/CORE/no-elf-ama-symbol.ll b/llvm/test/CodeGen/BPF/CORE/no-elf-ama-symbol.ll
new file mode 100644
index 00000000000..8851c502b6f
--- /dev/null
+++ b/llvm/test/CodeGen/BPF/CORE/no-elf-ama-symbol.ll
@@ -0,0 +1,65 @@
+; RUN: llc -march=bpfel -filetype=obj -o - %s | llvm-readelf -s | FileCheck -check-prefixes=CHECK %s
+; RUN: llc -march=bpfeb -filetype=obj -o - %s | llvm-readelf -s | FileCheck -check-prefixes=CHECK %s
+; RUN: llc -march=bpfel -filetype=obj -addrsig -o - %s | llvm-readelf -s | FileCheck -check-prefixes=CHECK %s
+; RUN: llc -march=bpfeb -filetype=obj -addrsig -o - %s | llvm-readelf -s | FileCheck -check-prefixes=CHECK %s
+;
+; Source Code:
+;   struct tt { int a; } __attribute__((preserve_access_index));
+;   int test(struct tt *arg) {
+;     return arg->a;
+;   }
+; Compilation flag:
+;   clang -target bpf -O2 -g -S -emit-llvm t.c
+
+%struct.tt = type { i32 }
+
+; Function Attrs: nounwind readonly
+define dso_local i32 @test(%struct.tt* readonly %arg) local_unnamed_addr #0 !dbg !7 {
+entry:
+  call void @llvm.dbg.value(metadata %struct.tt* %arg, metadata !16, metadata !DIExpression()), !dbg !17
+  %0 = tail call i32* @llvm.preserve.struct.access.index.p0i32.p0s_struct.tts(%struct.tt* %arg, i32 0, i32 0), !dbg !18, !llvm.preserve.access.index !12
+  %1 = load i32, i32* %0, align 4, !dbg !18, !tbaa !19
+  ret i32 %1, !dbg !24
+}
+
+; CHECK-NOT: llvm.tt:0:0$0:0
+
+; Function Attrs: nounwind readnone
+declare i32* @llvm.preserve.struct.access.index.p0i32.p0s_struct.tts(%struct.tt*, i32, i32) #1
+
+; Function Attrs: nounwind readnone speculatable
+declare void @llvm.dbg.value(metadata, metadata, metadata) #2
+
+attributes #0 = { nounwind readonly "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="all" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { nounwind readnone }
+attributes #2 = { nounwind readnone speculatable}
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 10.0.0 (https://github.com/llvm/llvm-project.git 947f9692440836dcb8d88b74b69dd379d85974ce)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, nameTableKind: None)
+!1 = !DIFile(filename: "test.c", directory: "/tmp/home/yhs/work/tests/bug")
+!2 = !{}
+!3 = !{i32 7, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang version 10.0.0 (https://github.com/llvm/llvm-project.git 947f9692440836dcb8d88b74b69dd379d85974ce)"}
+!7 = distinct !DISubprogram(name: "test", scope: !1, file: !1, line: 2, type: !8, scopeLine: 2, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !15)
+!8 = !DISubroutineType(types: !9)
+!9 = !{!10, !11}
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !12, size: 64)
+!12 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "tt", file: !1, line: 1, size: 32, elements: !13)
+!13 = !{!14}
+!14 = !DIDerivedType(tag: DW_TAG_member, name: "a", scope: !12, file: !1, line: 1, baseType: !10, size: 32)
+!15 = !{!16}
+!16 = !DILocalVariable(name: "arg", arg: 1, scope: !7, file: !1, line: 2, type: !11)
+!17 = !DILocation(line: 0, scope: !7)
+!18 = !DILocation(line: 3, column: 15, scope: !7)
+!19 = !{!20, !21, i64 0}
+!20 = !{!"tt", !21, i64 0}
+!21 = !{!"int", !22, i64 0}
+!22 = !{!"omnipotent char", !23, i64 0}
+!23 = !{!"Simple C/C++ TBAA"}
+!24 = !DILocation(line: 3, column: 3, scope: !7)