Don't populate the symbol table with symbols that don't belong to a section with the flag SHF_ALLOC

[gw280]

Summary

When populating the symbol table for an ELF object file, don't insert any symbols that come from ELF sections which don't have runtime allocated memory (typically debugging symbols).

[dblaikie]

Looks good - one minor change to drop braces from the if. (I can make this change myself if I'm submitting it for you)

Do you need me to submit this for you? (if you don't have LLVM commit access)

llvm/lib/DebugInfo/Symbolize/SymbolizableObjectFile.cpp

174–176

https://llvm.org/docs/CodingStandards.html#don-t-use-braces-on-simple-single-statement-bodies-of-if-else-loop-statements

[gw280]

In D133795#3787210, @dblaikie wrote:

Looks good - one minor change to drop braces from the if. (I can make this change myself if I'm submitting it for you)

Do you need me to submit this for you? (if you don't have LLVM commit access)

If you could commit it that'd be great. I do not have commit access. Thanks!

[mizvekov]

llvm/lib/DebugInfo/Symbolize/SymbolizableObjectFile.cpp

173

We generally prefer that, though it does seem unnecessary to declare that for a single use.
Might as well do: if ((Sec.get()->getFlags() & ELF::SHF_ALLOC) == 0))

llvm/lib/DebugInfo/Symbolize/SymbolizableObjectFile.cpp

if (!Sec || Obj.section_end() == *Sec) {
     return Error::success();
   }
 
   Expected<SymbolRef::Type> SymbolTypeOrErr = Symbol.getType();
   if (!SymbolTypeOrErr)
     return SymbolTypeOrErr.takeError();
   SymbolRef::Type SymbolType = *SymbolTypeOrErr;
   if (Obj.isELF()) {
+    // Ignore any symbols coming from sections that don't have runtime
+    // allocated memory.
+    if ((elf_section_iterator(*Sec)->getFlags() & ELF::SHF_ALLOC) == 0)
+      return Error::success();
+
     // 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 STT_SECTION and
     // ARM mapping symbols.
     uint32_t Flags = cantFail(Symbol.getFlags());

llvm/test/DebugInfo/Symbolize/ELF/symtab-file2.yaml

- Name:  .text
     Flags: [ SHF_ALLOC, SHF_EXECINSTR ]
     Size:  1
 Symbols:
   - StName:  0xffff
     Type:    STT_FILE
     Index:   SHN_ABS
   - Name:    local
     Section: .text
+
+# RUN: yaml2obj --docnum=3 %s -o %t3
+# RUN: llvm-symbolizer --obj=%t3 'DATA 0x1001' 2>&1 | FileCheck %s --check-prefix=CHECK3
+
+# CHECK3:      code
+# CHECK3-NEXT: 4096 2
+# CHECK3-NEXT: ??:?
+# CHECK3-EMPTY:
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_DYN
+  Machine: EM_X86_64
+Sections:
+  - Name:    .text
+    Type:    SHT_PROGBITS
+    Flags:   [ SHF_ALLOC, SHF_EXECINSTR ]
+    Address: 0x1000
+    Size:    1
+  - Name:    .debug
+    Type:    SHT_PROGBITS
+    Address: 0x0000
+    Size:    0xFFFF
+Symbols:
+  - Name:    debug
+    Section: .debug
+    Binding: STB_WEAK
+    Value:   0x1001
+    Size:    0
+  - Name:    code
+    Section: .text
+    Binding: STB_WEAK
+    Value:   0x1000
+    Size:    2