[PATCH] D58146: [symbolizer] Avoid collecting symbols belonging to invalid sections.

Matt Davis via Phabricator via llvm-commits llvm-commits at lists.llvm.org
Tue Feb 12 13:45:26 PST 2019

mattd created this revision.
mattd added reviewers: jhenderson, rupprecht.
Herald added a subscriber: hiraditya.
Herald added a project: LLVM.

llvm-symbolizer would originally report symbols that belonged to an invalid object file section. 
Specifically the case where: `*Symbol.getSection() == ObjFile.section_end()`
This patch prevents the Symbolizer from collecting symbols that belong to invalid sections.

The test  (from PR40591) introduces a case where two symbols have address 0,
one symbol is defined, 'foo', and the other is not defined, 'bar'.  This patch will cause
the Symbolizer to keep 'foo' and ignore 'bar'.

As a side note, the logic for adding symbols to the Symbolizer's store
(`SymbolizableObjectFile::addSymbol`) replaces symbols with the
same <address, size> pair.  At some point that logic should be revisited as in the
aforementioned case, 'bar' was overwriting 'foo' in the Symbolizer's store,
and 'foo' was forgotten.

This fixes PR40591



Index: llvm/test/tools/llvm-symbolizer/ignore-undefined-symbols.s
--- /dev/null
+++ llvm/test/tools/llvm-symbolizer/ignore-undefined-symbols.s
@@ -0,0 +1,12 @@
+# REQUIRES: x86-registered-target
+# RUN: llvm-mc --filetype=obj --triple=x86_64-pc-linux %s -o %t.o -g
+# RUN: llvm-symbolizer --obj=%t.o 0 | FileCheck %s --implicit-check-not=bar
+# CHECK:      foo
+# CHECK-NEXT: ignore-undefined-symbols.s:12:0
+.type bar, at function
+.type foo, at function
+.global foo
+    call bar
Index: llvm/lib/DebugInfo/Symbolize/SymbolizableObjectFile.cpp
--- llvm/lib/DebugInfo/Symbolize/SymbolizableObjectFile.cpp
+++ llvm/lib/DebugInfo/Symbolize/SymbolizableObjectFile.cpp
@@ -136,6 +136,11 @@
                                                   uint64_t SymbolSize,
                                                   DataExtractor *OpdExtractor,
                                                   uint64_t OpdAddress) {
+  // Avoid adding symbols from an unknown/undefined section.
+  const ObjectFile *Obj = Symbol.getObject();
+  Expected<section_iterator> Sec = Symbol.getSection();
+  if (!Sec || (Obj && Obj->section_end() == *Sec))
+    return std::error_code();
   Expected<SymbolRef::Type> SymbolTypeOrErr = Symbol.getType();
   if (!SymbolTypeOrErr)
     return errorToErrorCode(SymbolTypeOrErr.takeError());

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