[MC] Fix DWARF forms for 64-bit DWARFv3 files [6/7]

[ikudrin]

Summary

DW_FORM_sec_offset was introduced in DWARFv4, so, for 64-bit DWARFv3, DW_FORM_data8 should be used instead.

[dblaikie]

Looks good - thanks!

[MaskRay]

With one test change

llvm/test/MC/ELF/gen-dwarf64.s

4

--check-prefixes=REL,REL3

17

This REL can be REL-NEXT to prevent the accidental omission of check-prefixes=REL,REL3

[jhenderson]

LGTM, once @MaskRay's comments have been addressed.

[ikudrin]

• Fixed the test.

[ikudrin]

llvm/test/MC/ELF/gen-dwarf64.s

4

Thanks!

17

There are other relocations for the .debug_info section which I did not want to check because they are irrelevant to the changes of these patches. So, I probably would not add the -NEXT suffix, if you do not mind.

[dblaikie]

llvm/test/MC/ELF/gen-dwarf64.s

17

At least a "REL-NOT: }" to check that you haven't accidentally jumped into another section's relocations might be useful? But really that'd have to go between every one of these check lines.

Perhaps llvm-readobj has flags that specify which sections to dump - and if you only dump the relocations for the sections you're interested in, then you could use an --implicit-check-not: Section, for instance - to ensure you didn't jump over any section headers.

[ikudrin]

llvm/test/MC/ELF/gen-dwarf64.s

17

You probably meant "REL-NOT: {", but that still would not have helped with missed ,REL3.

[jhenderson]

llvm/test/MC/ELF/gen-dwarf64.s

17

You could add a REL: } check to mark the end of the .rela.debug_info, which would allow for the next bit to be REL-NEXT, but that also wouldn't solve the problem.

This sounds like one of those FileCheck gotchas, and I can't see much we can do in the test to avoid it in this case. You could maybe use something like --implicit-check-not=.debug to show that there are no relocations targeting debug sections in the output except for those explicitly checked, maybe?

[ikudrin]

• Added --implicit-check-not="R_{{.*}} .debug_" to the test to ensure that all relocations to debug sections are checked.

llvm/test/MC/ELF/gen-dwarf64.s

17

That's a marvellous idea, thanks! I'll add --implicit-check-not="R_{{.*}} .debug_" to D81146 and D81148.

llvm/lib/MC/MCDwarf.cpp

 static void EmitGenDwarfAbbrev(MCStreamer *MCOS) {
   MCContext &context = MCOS->getContext();
   MCOS->SwitchSection(context.getObjectFileInfo()->getDwarfAbbrevSection());
 
   // DW_TAG_compile_unit DIE abbrev (1).
   MCOS->emitULEB128IntValue(1);
   MCOS->emitULEB128IntValue(dwarf::DW_TAG_compile_unit);
   MCOS->emitInt8(dwarf::DW_CHILDREN_yes);
-  EmitAbbrev(MCOS, dwarf::DW_AT_stmt_list, context.getDwarfVersion() >= 4
-                                               ? dwarf::DW_FORM_sec_offset
+  dwarf::Form SecOffsetForm =
+      context.getDwarfVersion() >= 4
+          : (context.getDwarfFormat() == dwarf::DWARF64 ? dwarf::DW_FORM_data8
                                                         : dwarf::DW_FORM_data4);
+  EmitAbbrev(MCOS, dwarf::DW_AT_stmt_list, SecOffsetForm);
   if (context.getGenDwarfSectionSyms().size() > 1 &&
       context.getDwarfVersion() >= 3) {
-    EmitAbbrev(MCOS, dwarf::DW_AT_ranges, context.getDwarfVersion() >= 4
-                                              ? dwarf::DW_FORM_sec_offset
-                                              : dwarf::DW_FORM_data4);
+    EmitAbbrev(MCOS, dwarf::DW_AT_ranges, SecOffsetForm);
   } else {
     EmitAbbrev(MCOS, dwarf::DW_AT_low_pc, dwarf::DW_FORM_addr);
     EmitAbbrev(MCOS, dwarf::DW_AT_high_pc, dwarf::DW_FORM_addr);
   }
   EmitAbbrev(MCOS, dwarf::DW_AT_name, dwarf::DW_FORM_string);
   if (!context.getCompilationDir().empty())
     EmitAbbrev(MCOS, dwarf::DW_AT_comp_dir, dwarf::DW_FORM_string);
   StringRef DwarfDebugFlags = context.getDwarfDebugFlags();

llvm/test/MC/ELF/gen-dwarf64.s

 ## This checks that llvm-mc is able to produce 64-bit debug info.
 
+# RUN: llvm-mc -g -dwarf-version 3 -dwarf64 -triple x86_64 %s -filetype=obj -o %t3.o
+# RUN: llvm-readobj -r %t3.o | FileCheck --check-prefixes=REL,REL3 %s --implicit-check-not="R_{{.*}} .debug_"
+# RUN: llvm-dwarfdump -v %t3.o | FileCheck --check-prefixes=DUMP,DUMP3 %s
+
 # RUN: llvm-mc -g -dwarf-version 5 -dwarf64 -triple x86_64 %s -filetype=obj -o %t5.o
 # RUN: llvm-readobj -r %t5.o | FileCheck --check-prefixes=REL,REL5 %s --implicit-check-not="R_{{.*}} .debug_"
 # RUN: llvm-dwarfdump -v %t5.o | FileCheck --check-prefixes=DUMP,DUMP5 %s
 
 ## The references to other debug info sections are 64-bit, as required for DWARF64.
 # REL:         Section ({{[0-9]+}}) .rela.debug_info {
 # REL-NEXT:      R_X86_64_64 .debug_abbrev 0x0
 # REL-NEXT:      R_X86_64_64 .debug_line 0x0
+# REL3-NEXT:     R_X86_64_64 .debug_ranges 0x0
 # REL5-NEXT:     R_X86_64_64 .debug_rnglists 0x14
 # REL:         Section ({{[0-9]+}}) .rela.debug_aranges {
 # REL-NEXT:      R_X86_64_64 .debug_info 0x0
 # REL5:        Section ({{[0-9]+}}) .rela.debug_line {
 # REL5-NEXT:     R_X86_64_64 .debug_line_str 0x0
 # REL5-NEXT:     R_X86_64_64 .debug_line_str 0x
 
+## DW_FORM_sec_offset was introduced in DWARFv4.
+## For DWARFv3, DW_FORM_data8 is used instead.
+# DUMP:       .debug_abbrev contents:
+# DUMP3:        DW_AT_stmt_list DW_FORM_data8
+# DUMP3-NEXT:   DW_AT_ranges    DW_FORM_data8
+# DUMP5:        DW_AT_stmt_list DW_FORM_sec_offset
+# DUMP5-NEXT:   DW_AT_ranges    DW_FORM_sec_offset
+
 # DUMP:       .debug_info contents:
 # DUMP-NEXT:  0x00000000: Compile Unit: {{.*}} format = DWARF64
 # DUMP:       DW_TAG_compile_unit [1] *
+# DUMP3-NEXT:   DW_AT_stmt_list [DW_FORM_data8] (0x0000000000000000)
 # DUMP5-NEXT:   DW_AT_stmt_list [DW_FORM_sec_offset] (0x0000000000000000)
+# DUMP3-NEXT:   DW_AT_ranges [DW_FORM_data8] (0x0000000000000000
 # DUMP5-NEXT:   DW_AT_ranges [DW_FORM_sec_offset] (0x0000000000000014
 # DUMP-NEXT:      [0x0000000000000000, 0x0000000000000001) ".foo"
 # DUMP-NEXT:      [0x0000000000000000, 0x0000000000000001) ".bar")
 # DUMP:       DW_TAG_label [2]
 # DUMP-NEXT:    DW_AT_name [DW_FORM_string] ("foo")
 # DUMP:       DW_TAG_label [2]
 # DUMP-NEXT:    DW_AT_name [DW_FORM_string] ("bar")
 

 # DUMP5-NEXT: file_names[  0]:
 # DUMP5-NEXT:            name: .debug_line_str[0x00000000[[FILEOFF:[[:xdigit:]]{8}]]] = "[[FILE:.+]]"
 # DUMP5-NEXT:       dir_index: 0
 
 # DUMP5:      .debug_line_str contents:
 # DUMP5-NEXT: 0x00000000: "[[DIR]]"
 # DUMP5-NEXT: 0x[[FILEOFF]]: "[[FILE]]"
 
+# DUMP3:      .debug_ranges contents:
+# DUMP3-NEXT: 00000000 ffffffffffffffff 0000000000000000
+# DUMP3-NEXT: 00000000 0000000000000000 0000000000000001
+# DUMP3-NEXT: 00000000 ffffffffffffffff 0000000000000000
+# DUMP3-NEXT: 00000000 0000000000000000 0000000000000001
+# DUMP3-NEXT: 00000000 <End of list>
+
 # DUMP5:      .debug_rnglists contents:
 # DUMP5-NEXT: 0x00000000: range list header: length = 0x000000000000001d, format = DWARF64, version = 0x0005, addr_size = 0x08, seg_size = 0x00, offset_entry_count = 0x00000000
 # DUMP5-NEXT: ranges:
 # DUMP5-NEXT: 0x00000014: [DW_RLE_start_length]: 0x0000000000000000, 0x0000000000000001 => [0x0000000000000000, 0x0000000000000001)
 # DUMP5-NEXT: 0x0000001e: [DW_RLE_start_length]: 0x0000000000000000, 0x0000000000000001 => [0x0000000000000000, 0x0000000000000001)
 # DUMP5-NEXT: 0x00000028: [DW_RLE_end_of_list ]
 
     .section .foo, "ax", @progbits
 foo:
     nop
 
     .section .bar, "ax", @progbits
 bar:
     nop