[BPF] Fix bpf llvm-objdump issues

[yonghong-song]

Summary

Commit https://reviews.llvm.org/D57939 ("[DWARF] Refactor
RelocVisitor and fix computation of SHT_RELA-typed relocation entries)
made a change for relocation resolution when operating
on an object file.

The change unfortunately broke BPF as given SymbolValue (S) and
Addent (A), previously relocation is resolved to

S + A

and after the change, it is resolved to

S

This patch fixed the issue by resolving relocation correctly.

It looks not all relocation resolution reaches here and I did not
trace down exactly when. But I do find if the object file includes
codes in two different ELF sections than default ".text",
the above bug will be triggered.

This patch included a trivial two function source code to
demonstrate this issue. The relocation for .debug_loc is resolved
incorrectly due to this and llvm-objdump cannot display source
annotated assembly.

[MaskRay]

llvm/test/CodeGen/BPF/objdump_two_funcs.ll

48 ↗

(On Diff #215715)

Can you clean up these metadata tags? A lot of attributes, e.g directory, checksum, source, clang version, DILocation, etc, are not needed.

[yonghong-song]

llvm/test/CodeGen/BPF/objdump_two_funcs.ll

48 ↗

(On Diff #215715)

I need this to have reliable source in llvm-objdump -S.

llvm/trunk/lib/Object/RelocationResolver.cpp

static bool supportsBPF(uint64_t Type) {
   default:
     return false;
   }
 }
 
 static uint64_t resolveBPF(RelocationRef R, uint64_t S, uint64_t A) {
   switch (R.getType()) {
   case ELF::R_BPF_64_32:
-    return S & 0xFFFFFFFF;
+    return (S + A) & 0xFFFFFFFF;
   case ELF::R_BPF_64_64:
-    return S;
+    return S + A;
   default:
     llvm_unreachable("Invalid relocation type");
   }
 }
 
 static bool supportsMips64(uint64_t Type) {
   switch (Type) {
   case ELF::R_MIPS_32:

llvm/trunk/test/CodeGen/BPF/objdump_two_funcs.ll

+; RUN: llc -march=bpfel -filetype=obj -o - %s | llvm-objdump -S - | FileCheck %s
+; RUN: llc -march=bpfeb -filetype=obj -o - %s | llvm-objdump -S - | FileCheck %s
+;
+; Source code:
+;   __attribute__((section("s1")))
+;   int func1(int a) {
+;       return a * a;
+;   }
+;   __attribute__((section("s2")))
+;   int func2(int a) {
+;       return a * a * a;
+;   }
+; Compiler flag to generate IR:
+;   clang -target bpf -S -gdwarf-5 -gembed-source -emit-llvm -g -O2 bug.c
+
+; Function Attrs: norecurse nounwind readnone
+define dso_local i32 @func1(i32 %a) local_unnamed_addr #0 section "s1" !dbg !7 {
+entry:
+; CHECK: func1:
+  call void @llvm.dbg.value(metadata i32 %a, metadata !12, metadata !DIExpression()), !dbg !13
+  %mul = mul nsw i32 %a, %a, !dbg !14
+  ret i32 %mul, !dbg !15
+; CHECK: ; return a * a;
+}
+
+; Function Attrs: norecurse nounwind readnone
+define dso_local i32 @func2(i32 %a) local_unnamed_addr #0 section "s2" !dbg !16 {
+entry:
+; CHECK: func2:
+  call void @llvm.dbg.value(metadata i32 %a, metadata !18, metadata !DIExpression()), !dbg !19
+  %mul = mul nsw i32 %a, %a, !dbg !20
+  %mul1 = mul nsw i32 %mul, %a, !dbg !21
+  ret i32 %mul1, !dbg !22
+; CHECK: ; return a * a * a;
+}
+
+; Function Attrs: nounwind readnone speculatable
+declare void @llvm.dbg.value(metadata, metadata, metadata) #1
+
+attributes #0 = { norecurse nounwind readnone "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "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 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 9.0.0 (trunk 366422) (llvm/trunk 366423)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, nameTableKind: None)
+!1 = !DIFile(filename: "bug.c", directory: "/tmp/home/yhs/work/tests/llvm/reloc", checksumkind: CSK_MD5, checksum: "c7c9938d4e6989ca33db748213aab194", source: "__attribute__((section(\22s1\22)))\0Aint func1(int a) {\0A    return a * a;\0A}\0A__attribute__((section(\22s2\22)))\0Aint func2(int a) {\0A    return a * a * a;\0A}\0A")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 5}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang version 9.0.0 (trunk 366422) (llvm/trunk 366423)"}
+!7 = distinct !DISubprogram(name: "func1", scope: !1, file: !1, line: 2, type: !8, scopeLine: 2, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !11)
+!8 = !DISubroutineType(types: !9)
+!9 = !{!10, !10}
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = !{!12}
+!12 = !DILocalVariable(name: "a", arg: 1, scope: !7, file: !1, line: 2, type: !10)
+!13 = !DILocation(line: 0, scope: !7)
+!14 = !DILocation(line: 3, column: 14, scope: !7)
+!15 = !DILocation(line: 3, column: 5, scope: !7)
+!16 = distinct !DISubprogram(name: "func2", scope: !1, file: !1, line: 6, type: !8, scopeLine: 6, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !17)
+!17 = !{!18}
+!18 = !DILocalVariable(name: "a", arg: 1, scope: !16, file: !1, line: 6, type: !10)
+!19 = !DILocation(line: 0, scope: !16)
+!20 = !DILocation(line: 7, column: 14, scope: !16)
+!21 = !DILocation(line: 7, column: 18, scope: !16)
+!22 = !DILocation(line: 7, column: 5, scope: !16)