DebugInfo/Symbolize: Exclude ARM mapping symbols for .symtab symbolization after D95916

[MaskRay]

Summary

Their names don't convey much information, so they should be excluded.
The behavior matches addr2line.

[zatrazz]

LGTM, it fixes the arm sanitizer regressions.

llvm/lib/DebugInfo/Symbolize/SymbolizableObjectFile.cpp

Error SymbolizableObjectFile::addSymbol(const SymbolRef &Symbol,
   SymbolRef::Type SymbolType = *SymbolTypeOrErr;
   if (Obj.isELF()) {
     // Allow function and data symbols. Additionally allow STT_NONE, which are
     // common for functions defined in assembly.
     uint8_t Type = ELFSymbolRef(Symbol).getELFType();
     if (Type != ELF::STT_NOTYPE && Type != ELF::STT_FUNC &&
         Type != ELF::STT_OBJECT && Type != ELF::STT_GNU_IFUNC)
       return Error::success();
+    // Some STT_NOTYPE symbols are not desired. This excludes ARM mapping
+    // symbols.
+    uint32_t Flags = cantFail(Symbol.getFlags());
+    if (Flags & SymbolRef::SF_FormatSpecific)
+      return Error::success();
   } else if (SymbolType != SymbolRef::ST_Function &&
              SymbolType != SymbolRef::ST_Data) {
     return Error::success();
   }
 
   Expected<uint64_t> SymbolAddressOrErr = Symbol.getAddress();
   if (!SymbolAddressOrErr)
     return SymbolAddressOrErr.takeError();

llvm/test/DebugInfo/Symbolize/ELF/arm-mapping-symbol.s

+# REQUIRES: arm-registered-target
+## Ignore ARM mapping symbols (with a prefix of $a, $d or $t).
+
+# RUN: llvm-mc -filetype=obj -triple=armv7-none-linux %s -o %t
+# RUN: llvm-symbolizer --obj=%t 4 8 | FileCheck %s
+# RUN: llvm-mc -filetype=obj -triple=thumbv7-none-linux %s -o %tthumb
+# RUN: llvm-symbolizer --obj=%tthumb 4 8 | FileCheck %s
+
+# CHECK:       foo
+# CHECK-NEXT:  ??:0:0
+# CHECK-EMPTY:
+# CHECK-NEXT:  foo
+# CHECK-NEXT:  ??:0:0
+
+.globl foo
+foo:
+  .word 32
+  nop
+  .word 32