[MC][ELF] Do not error on parsing .debug_* section directive for MIPS

[atanasyan]

Summary

MIPS .debug_* sections should have SHT_MIPS_DWARF section type to distinguish among sections contain DWARF and ECOFF debug formats, but in assembly files these sections have SHT_PROGBITS (@progbits) type. Now assembler shows 'changed section type for ...' error when parsing .section .debug_*,"",@progbits directive for MIPS targets.

The same problem exists for x86-64 target and this patch extends workaround implemented in D76151. The patch adds one more case when assembler ignore section types mismatch after SwitchSection() call.

[arichardson]

llvm/lib/MC/MCParser/ELFAsmParser.cpp

518

Should this be restricted to Section->getName().startsWith (".debug")?

[MaskRay]

MIPS .debug_* sections should have SHT_MIPS_DWARF section type to distinguish among sections contain DWARF and ECOFF debug formats

If SHT_PROGBITS is a valid value, now what's the value keeping using SHT_MIPS_DWARF?

I know the ELF spirit is preferring section types to section names, but the reality with at least the 32-bit DWARF format is that architectures should just stick with SHT_PROGBITS.
For compatibility, consumers need to keep recognizing SHT_MIPS_DWARF but producers can switch the type anytime.

That said, the patch LG.

[atanasyan]

llvm/lib/MC/MCParser/ELFAsmParser.cpp

518

Good point. I'll fix this.

[atanasyan]

In D107707#2933312, @MaskRay wrote:

MIPS .debug_* sections should have SHT_MIPS_DWARF section type to distinguish among sections contain DWARF and ECOFF debug formats

If SHT_PROGBITS is a valid value, now what's the value keeping using SHT_MIPS_DWARF?

As usual for MIPS the main reason is compatibility with other tools.

[atanasyan]

• Check section name prefix .debug_ instead of section type. This approach is closer to other MIPS toolchains.

[MaskRay]

Looks great!

[atanasyan]

Thanks for review.

llvm/lib/MC/MCParser/ELFAsmParser.cpp

if (!isUInt<32>(UniqueID) || UniqueID == ~0U)
     return TokError("unique id is too large");
   return false;
 }
 
 static bool hasPrefix(StringRef SectionName, StringRef Prefix) {
   return SectionName.startswith(Prefix) || SectionName == Prefix.drop_back();
 }
 
+static bool allowSectionTypeMismatch(const Triple &TT, StringRef SectionName,
+                                     unsigned Type) {
+  if (TT.getArch() == Triple::x86_64) {
+    // x86-64 psABI names SHT_X86_64_UNWIND as the canonical type for .eh_frame,
+    // but GNU as emits SHT_PROGBITS .eh_frame for .cfi_* directives. Don't
+    // error for SHT_PROGBITS .eh_frame
+    return SectionName == ".eh_frame" && Type == ELF::SHT_PROGBITS;
+  }
+  if (TT.isMIPS()) {
+    // MIPS .debug_* sections should have SHT_MIPS_DWARF section type to
+    // distinguish among sections contain DWARF and ECOFF debug formats,
+    // but in assembly files these sections have SHT_PROGBITS type.
+    return hasPrefix(SectionName, ".debug_") && Type == ELF::SHT_PROGBITS;
+  }
+  return false;
+}
+
 bool ELFAsmParser::ParseSectionArguments(bool IsPush, SMLoc loc) {
   StringRef SectionName;
 
   if (ParseSectionName(SectionName))
     return TokError("expected identifier in directive");
 
   StringRef TypeName;
   int64_t Size = 0;
if (const MCSectionELF *Section =
         Flags |= ELF::SHF_GROUP;
       }
   }
 
   MCSectionELF *Section =
       getContext().getELFSection(SectionName, Type, Flags, Size, GroupName,
                                  IsComdat, UniqueID, LinkedToSym);
   getStreamer().SwitchSection(Section, Subsection);
-  // x86-64 psABI names SHT_X86_64_UNWIND as the canonical type for .eh_frame,
-  // but GNU as emits SHT_PROGBITS .eh_frame for .cfi_* directives. Don't error
-  // for SHT_PROGBITS .eh_frame
   if (Section->getType() != Type &&
-      !(SectionName == ".eh_frame" && Type == ELF::SHT_PROGBITS))
+      !allowSectionTypeMismatch(getContext().getTargetTriple(), SectionName,
+                                Type))
     Error(loc, "changed section type for " + SectionName + ", expected: 0x" +
                    utohexstr(Section->getType()));
   // Check that flags are used consistently. However, the GNU assembler permits
   // to leave out in subsequent uses of the same sections; for compatibility,
   // do likewise.
   if ((extraFlags || Size || !TypeName.empty()) && Section->getFlags() != Flags)
     Error(loc, "changed section flags for " + SectionName + ", expected: 0x" +
                    utohexstr(Section->getFlags()));

llvm/test/MC/Mips/elf-debug-section.s

 # RUN: llvm-mc -filetype=obj -triple=mips-linux-gnu -g %s -o - \
 # RUN:   | llvm-readobj -S - | FileCheck %s
 
+# MIPS .debug_* sections should have SHT_MIPS_DWARF section type
+# to distinguish among sections contain DWARF and ECOFF debug formats,
+# but in assembly files these sections have SHT_PROGBITS type.
+
+.section        .debug_abbrev,"",@progbits
+.section        .debug_addr,"",@progbits
+.section        .debug_aranges,"",@progbits
+.section        .debug_info,"",@progbits
+.section        .debug_line,"",@progbits
+.section        .debug_loclists,"",@progbits
+.section        .debug_pubnames,"",@progbits
+.section        .debug_pubtypes,"",@progbits
+.section        .debug_ranges,"",@progbits
+.section        .debug_rnglists,"",@progbits
+.section        .debug_str,"MS",@progbits,1
+
 # CHECK:      Section {
+# CHECK:        Name: .debug_abbrev
+# CHECK-NEXT:   Type: SHT_MIPS_DWARF
+# CHECK:        Name: .debug_addr
+# CHECK-NEXT:   Type: SHT_MIPS_DWARF
+# CHECK:        Name: .debug_aranges
+# CHECK-NEXT:   Type: SHT_MIPS_DWARF
+# CHECK:        Name: .debug_info
+# CHECK-NEXT:   Type: SHT_MIPS_DWARF
 # CHECK:        Name: .debug_line
-# CHECK-NEXT:   Type: SHT_MIPS_DWARF (0x7000001E)
+# CHECK-NEXT:   Type: SHT_MIPS_DWARF
+# CHECK:        Name: .debug_loclists
+# CHECK-NEXT:   Type: SHT_MIPS_DWARF
+# CHECK:        Name: .debug_pubnames
+# CHECK-NEXT:   Type: SHT_MIPS_DWARF
+# CHECK:        Name: .debug_pubtypes
+# CHECK-NEXT:   Type: SHT_MIPS_DWARF
+# CHECK:        Name: .debug_ranges
+# CHECK-NEXT:   Type: SHT_MIPS_DWARF
+# CHECK:        Name: .debug_rnglists
+# CHECK-NEXT:   Type: SHT_MIPS_DWARF
+# CHECK:        Name: .debug_str
+# CHECK-NEXT:   Type: SHT_MIPS_DWARF