[BPF] [BTF] Process FileName with absolute path correctly

In IR, sometimes the following attributes for DIFile may be
generated:
  filename: /home/yhs/test.c
  directory: /tmp
The /tmp may represent the working directory of the compilation
process.

In such cases, since filename is with absolute path,
the directory should be ignored by BTF. The filename alone is
enough to get the source.

Acked-by: Alexei Starovoitov <[email protected]>
Signed-off-by: Yonghong Song <[email protected]>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@352952 91177308-0d34-0410-b5e6-96231b3b80d8

Author: yonghong-song

lib/Target/BPF/BTFDebug.cpp

@@ -493,7 +493,7 @@ std::string BTFDebug::populateFileContent(const DISubprogram *SP) {
   auto File = SP->getFile();
   std::string FileName;
 
-  if (File->getDirectory().size())
+  if (!File->getFilename().startswith("/") && File->getDirectory().size())
     FileName = File->getDirectory().str() + "/" + File->getFilename().str();
   else
     FileName = File->getFilename();

test/CodeGen/BPF/BTF/filename.ll

@@ -0,0 +1,81 @@
+; RUN: llc -march=bpfel -filetype=asm -o - %s | FileCheck -check-prefixes=CHECK %s
+; RUN: llc -march=bpfeb -filetype=asm -o - %s | FileCheck -check-prefixes=CHECK %s
+
+; Source code:
+;   int test() { return 0; }
+; Compilation flag:
+;   clang -target bpf -O2 -g -S -emit-llvm t.c
+
+; Function Attrs: norecurse nounwind readnone uwtable
+define dso_local i32 @test() local_unnamed_addr #0 !dbg !7 {
+  ret i32 0, !dbg !11
+}
+
+; CHECK:             .section        .BTF,"",@progbits
+; CHECK-NEXT:        .short  60319                   # 0xeb9f
+; CHECK-NEXT:        .byte   1
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .long   24
+; CHECK-NEXT:        .long   0
+; CHECK-NEXT:        .long   40
+; CHECK-NEXT:        .long   40
+; CHECK-NEXT:        .long   35
+; CHECK-NEXT:        .long   0                       # BTF_KIND_FUNC_PROTO(id = 1)
+; CHECK-NEXT:        .long   218103808               # 0xd000000
+; CHECK-NEXT:        .long   2
+; CHECK-NEXT:        .long   26                      # BTF_KIND_INT(id = 2)
+; CHECK-NEXT:        .long   16777216                # 0x1000000
+; CHECK-NEXT:        .long   4
+; CHECK-NEXT:        .long   16777248                # 0x1000020
+; CHECK-NEXT:        .long   30                      # BTF_KIND_FUNC(id = 3)
+; CHECK-NEXT:        .long   201326592               # 0xc000000
+; CHECK-NEXT:        .long   1
+; CHECK-NEXT:        .byte   0                       # string offset=0
+; CHECK-NEXT:        .ascii  ".text"                 # string offset=1
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "/home/yhs/ttmp/t.c"    # string offset=7
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "int"                   # string offset=26
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .ascii  "test"                  # string offset=30
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .section        .BTF.ext,"",@progbits
+; CHECK-NEXT:        .short  60319                   # 0xeb9f
+; CHECK-NEXT:        .byte   1
+; CHECK-NEXT:        .byte   0
+; CHECK-NEXT:        .long   24
+; CHECK-NEXT:        .long   0
+; CHECK-NEXT:        .long   20
+; CHECK-NEXT:        .long   20
+; CHECK-NEXT:        .long   28
+; CHECK-NEXT:        .long   8                       # FuncInfo
+; CHECK-NEXT:        .long   1                       # FuncInfo section string offset=1
+; CHECK-NEXT:        .long   1
+; CHECK-NEXT:        .long   .Lfunc_begin{{[0-9]+}}
+; CHECK-NEXT:        .long   3
+; CHECK-NEXT:        .long   16                      # LineInfo
+; CHECK-NEXT:        .long   1                       # LineInfo section string offset=1
+; CHECK-NEXT:        .long   1
+; CHECK-NEXT:        .long   .Ltmp{{[0-9]+}}
+; CHECK-NEXT:        .long   7
+; CHECK-NEXT:        .long   0
+; CHECK-NEXT:        .long   1038                    # Line 1 Col 14
+
+attributes #0 = { norecurse nounwind readnone uwtable "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "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" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+
+!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 8.0.20181009 ", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, nameTableKind: None)
+!1 = !DIFile(filename: "/home/yhs/ttmp/t.c", directory: "/home/yhs/ttmp")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang version 8.0.20181009 "}
+!7 = distinct !DISubprogram(name: "test", scope: !1, file: !1, line: 1, type: !8, isLocal: false, isDefinition: true, scopeLine: 1, isOptimized: true, unit: !0, retainedNodes: !2)
+!8 = !DISubroutineType(types: !9)
+!9 = !{!10}
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = !DILocation(line: 1, column: 14, scope: !7)