[BPF][DebugInfo] Show CO-RE relocations in llvm-objdump

Extend llvm-objdump to show CO-RE relocations when `-r` option is
passed and object file has .BTF and .BTF.ext sections.

For example, the following C program:

    #define __pai __attribute__((preserve_access_index))

    struct foo { int i; int j;} __pai;
    struct bar { struct foo f[7]; } __pai;
    extern void sink(void *);

    void root(struct bar *bar) {
      sink(&bar[2].f[3].j);
    }

Should lead to the following objdump output:

    $ clang --target=bpf -O2 -g t.c -c -o - | \
        llvm-objdump  --no-addresses --no-show-raw-insn -dr -

    ...
            r2 = 0x94
                    CO-RE <byte_off> [2] struct bar::[2].f[3].j (2:0:3:1)
            r1 += r2
            call -0x1
                    R_BPF_64_32     sink
            exit
    ...

More examples could be found in unit tests, see BTFParserTest.cpp.

To achieve this:
- Move CO-RE relocation kinds definitions from BPFCORE.h to BTF.h.
- Extend BTF.h with types derived from BTF::CommonType, e.g.
  BTF::IntType and BTF::StrutType, to allow dyn_cast() and access to
  type additional data.
- Extend BTFParser to load BTF type and relocation data.
- Modify llvm-objdump.cpp to create instance of BTFParser when
  disassembly of object file with BTF sections is processed and `-r`
  flag is supplied.

Additional information about CO-RE is available at [1].

[1] https://docs.kernel.org/bpf/llvm_reloc.html

Depends on D149058

Differential Revision: https://reviews.llvm.org/D150079

1 files changed, 30 insertions, 0 deletions

diff --git a/llvm/tools/llvm-objdump/llvm-objdump.cpp b/llvm/tools/llvm-objdump/llvm-objdump.cpp
index e4e1ceb..fcfce77 100644
--- a/llvm/tools/llvm-objdump/llvm-objdump.cpp
+++ b/llvm/tools/llvm-objdump/llvm-objdump.cpp
@@ -31,6 +31,7 @@
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/StringSet.h"
 #include "llvm/ADT/Twine.h"
+#include "llvm/DebugInfo/BTF/BTFParser.h"
 #include "llvm/DebugInfo/DWARF/DWARFContext.h"
 #include "llvm/DebugInfo/Symbolize/SymbolizableModule.h"
 #include "llvm/DebugInfo/Symbolize/Symbolize.h"
@@ -535,6 +536,22 @@ static void printRelocation(formatted_raw_ostream &OS, StringRef FileName,
   OS << Name << "\t" << Val;
 }
 
+static void printBTFRelocation(formatted_raw_ostream &FOS, llvm::BTFParser &BTF,
+                               object::SectionedAddress Address,
+                               LiveVariablePrinter &LVP) {
+  const llvm::BTF::BPFFieldReloc *Reloc = BTF.findFieldReloc(Address);
+  if (!Reloc)
+    return;
+
+  SmallString<64> Val;
+  BTF.symbolize(Reloc, Val);
+  FOS << "\t\t";
+  if (LeadingAddr)
+    FOS << format("%016" PRIx64 ":  ", Address.Address + AdjustVMA);
+  FOS << "CO-RE " << Val;
+  LVP.printAfterOtherLine(FOS, true);
+}
+
 class PrettyPrinter {
 public:
   virtual ~PrettyPrinter() = default;
@@ -1626,6 +1643,16 @@ disassembleObject(ObjectFile &Obj, const ObjectFile &DbgObj,
   if (SymbolizeOperands && !Obj.isRelocatableObject())
     ReadBBAddrMap();
 
+  std::optional<llvm::BTFParser> BTF;
+  if (InlineRelocs && BTFParser::hasBTFSections(Obj)) {
+    BTF.emplace();
+    BTFParser::ParseOptions Opts = {};
+    Opts.LoadTypes = true;
+    Opts.LoadRelocs = true;
+    if (Error E = BTF->parse(Obj, Opts))
+      WithColor::defaultErrorHandler(std::move(E));
+  }
+
   for (const SectionRef &Section : ToolSectionFilter(Obj)) {
     if (FilterSections.empty() && !DisassembleAll &&
         (!Section.isText() || Section.isVirtual()))
@@ -2163,6 +2190,9 @@ disassembleObject(ObjectFile &Obj, const ObjectFile &DbgObj,
                                 *DT->SubtargetInfo, CommentStream.str(), LVP);
         Comments.clear();
 
+        if (BTF)
+          printBTFRelocation(FOS, *BTF, {Index, Section.getIndex()}, LVP);
+
         // Hexagon does this in pretty printer
         if (Obj.getArch() != Triple::hexagon) {
           // Print relocation for instruction and data.