[dwarfdump] Add support for -debug-line=OFFSET

[JDevlieghere]

Summary

This patch adds support for passing an OFFSET to -debug-line.

[dblaikie]

Seems good

test/tools/llvm-dwarfdump/X86/debug_line_offset.test

1–11

I'd probably skip this test case? Or is there something interesting about the zero case?

[aprantl]

Without having checked out API yet — this is still traversing over all CUs to find the one with the entry. This could be slow for something like clang.dSYM. Is there a way to find the one CU containing the entry quicker? If not, this LGTM.

[JDevlieghere]

In D38240#880211, @aprantl wrote:

Without having checked out API yet — this is still traversing over all CUs to find the one with the entry. This could be slow for something like clang.dSYM. Is there a way to find the one CU containing the entry quicker? If not, this LGTM.

Except for the address byte size (for which other parts of the code use the hack below), we only need the offset.

uint8_t savedAddressByteSize = 0;
// FIXME: This seems sketchy.
for (const auto &CU : compile_units()) {
  savedAddressByteSize = CU->getAddressByteSize();
  break;
}

But that leaves us with the same issues as mentioned in D38237: we run into trouble when passing an invalid offset.

[aprantl]

Okay then let's solve the "let's deal with invalid offsets gracefully" separately.

lib/DebugInfo/DWARF/DWARFContext.cpp

void DWARFContext::dump(
   if (shouldDump(Explicit, ".debug_line", DIDT_ID_DebugLine,
                  DObj->getLineSection().Data)) {
     for (const auto &CU : compile_units()) {
       savedAddressByteSize = CU->getAddressByteSize();
       auto CUDIE = CU->getUnitDIE();
       if (!CUDIE)
         continue;
       if (auto StmtOffset = toSectionOffset(CUDIE.find(DW_AT_stmt_list))) {
+        if (DumpOffset && *StmtOffset != *DumpOffset)
+          continue;
         DWARFDataExtractor lineData(*DObj, DObj->getLineSection(),
                                     isLittleEndian(), savedAddressByteSize);
         DWARFDebugLine::LineTable LineTable;
         uint32_t Offset = *StmtOffset;
         // Verbose dumping is done during parsing and not on the intermediate
         // representation.
+        OS << "debug_line[" << format("%16.16" PRIx64, Offset) << "]\n";
         if (DumpOpts.Verbose) {
           LineTable.parse(lineData, &Offset, &OS);
         } else {
           LineTable.parse(lineData, &Offset);
           LineTable.dump(OS);
         }
       }
     }

test/tools/llvm-dwarfdump/X86/debug_line_offset.test

+RUN: llvm-dwarfdump %S/../../dsymutil/Inputs/basic-lto-dw4.macho.x86_64.o \
+RUN:  -debug-line=0x0 | FileCheck %s --check-prefix=CHECK-A
+
+CHECK-A: debug_line[0000000000000000]
+CHECK-A: Address            Line   Column File   ISA Discriminator Flags
+CHECK-A-NET: ------------------ ------ ------ ------ --- ------------- -------------
+CHECK-A-NET: 0x0000000000000000     26      0      1   0             0  is_stmt
+CHECK-A-NET: 0x0000000000000004     27     10      1   0             0  is_stmt prologue_end
+CHECK-A-NET: 0x0000000000000009     27      3      1   0             0
+CHECK-A-NET: 0x0000000000000074     27      3      1   0             0  end_sequence
+CHECK-A-NOT: debug_line[000000000000009a]
+
+RUN: llvm-dwarfdump %S/../../dsymutil/Inputs/basic-lto-dw4.macho.x86_64.o \
+RUN:  -debug-line=0x9a | FileCheck %s --check-prefix=CHECK-B
+
+CHECK-B-NOT: debug_line[0000000000000000]
+CHECK-B: debug_line[000000000000009a]
+CHECK-B: Address            Line   Column File   ISA Discriminator Flags
+CHECK-B-NEXT: ------------------ ------ ------ ------ --- ------------- -------------
+CHECK-B-NEXT: 0x0000000000000050     16      0      1   0             0  is_stmt
+CHECK-B-NEXT: 0x0000000000000054     12     10      1   0             0  is_stmt prologue_end
+CHECK-B-NEXT: 0x000000000000005a     17      7      1   0             0  is_stmt
+CHECK-B-NEXT: 0x000000000000005f     12     10      1   0             0  is_stmt
+CHECK-B-NEXT: 0x0000000000000067     20      1      1   0             0  is_stmt
+CHECK-B-NEXT: 0x0000000000000069     19     18      1   0             0  is_stmt
+CHECK-B-NEXT: 0x000000000000006b     19     10      1   0             0
+CHECK-B-NEXT: 0x0000000000000072     20      1      1   0             0  is_stmt
+CHECK-B-NEXT: 0x0000000000000074     20      1      1   0             0  is_stmt end_sequence