[lib/Object] - Make ELFObjectFile::getSymbol() return Expected<>.

This was requested in comments for D93209:
https://reviews.llvm.org/D93209#inline-871192

D93209 fixes an issue with `ELFFile<ELFT>::getEntry`,
after what `getSymbol` starts calling `report_fatal_error` for previously
missed invalid cases.

This patch makes it return `Expected<>` and updates callers.
For few of them I had to add new `report_fatal_error` calls. But I see no
way to avoid it currently. The change would affects too many places, e.g:
`getSymbolBinding` and other methods are used from `ELFSymbolRef`
which is used in too many places across LLVM.

Differential revision: https://reviews.llvm.org/D93297

1 files changed, 72 insertions, 0 deletions

diff --git a/llvm/unittests/Object/ELFObjectFileTest.cpp b/llvm/unittests/Object/ELFObjectFileTest.cpp
index 30be24c..aabb07c 100644
--- a/llvm/unittests/Object/ELFObjectFileTest.cpp
+++ b/llvm/unittests/Object/ELFObjectFileTest.cpp
@@ -397,3 +397,75 @@ ProgramHeaders:
   EXPECT_EQ((const char *)Data - Buf.getBufferStart(), 0x4000);
   EXPECT_EQ(Data[0], 0x99);
 }
+
+// This is a test for API that is related to symbols.
+// We check that errors are properly reported here.
+TEST(ELFObjectFileTest, InvalidSymbolTest) {
+  SmallString<0> Storage;
+  Expected<ELFObjectFile<ELF64LE>> ElfOrErr = toBinary<ELF64LE>(Storage, R"(
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_DYN
+  Machine: EM_X86_64
+Sections:
+  - Name: .symtab
+    Type: SHT_SYMTAB
+)");
+
+  ASSERT_THAT_EXPECTED(ElfOrErr, Succeeded());
+  const ELFFile<ELF64LE> &Elf = ElfOrErr->getELFFile();
+  const ELFObjectFile<ELF64LE> &Obj = *ElfOrErr;
+
+  Expected<const typename ELF64LE::Shdr *> SymtabSecOrErr = Elf.getSection(1);
+  ASSERT_THAT_EXPECTED(SymtabSecOrErr, Succeeded());
+  ASSERT_EQ((*SymtabSecOrErr)->sh_type, ELF::SHT_SYMTAB);
+
+  // We create a symbol with an index that is too large to exist in the object.
+  constexpr unsigned BrokenSymIndex = 0xFFFFFFFF;
+  ELFSymbolRef BrokenSym = Obj.toSymbolRef(*SymtabSecOrErr, BrokenSymIndex);
+
+  const char *ErrMsg = "unable to access section [index 1] data at "
+                       "0x1800000028: offset goes past the end of file";
+  // 1) Check the behavior of ELFObjectFile<ELFT>::getSymbolName().
+  //    SymbolRef::getName() calls it internally. We can't test it directly,
+  //    because it is protected.
+  EXPECT_THAT_ERROR(BrokenSym.getName().takeError(), FailedWithMessage(ErrMsg));
+
+  // 2) Check the behavior of ELFObjectFile<ELFT>::getSymbol().
+  EXPECT_THAT_ERROR(Obj.getSymbol(BrokenSym.getRawDataRefImpl()).takeError(),
+                    FailedWithMessage(ErrMsg));
+
+  // 3) Check the behavior of ELFObjectFile<ELFT>::getSymbolSection().
+  //    SymbolRef::getSection() calls it internally. We can't test it directly,
+  //    because it is protected.
+  EXPECT_THAT_ERROR(BrokenSym.getSection().takeError(),
+                    FailedWithMessage(ErrMsg));
+
+  // 4) Check the behavior of ELFObjectFile<ELFT>::getSymbolFlags().
+  //    SymbolRef::getFlags() calls it internally. We can't test it directly,
+  //    because it is protected.
+  EXPECT_THAT_ERROR(BrokenSym.getFlags().takeError(),
+                    FailedWithMessage(ErrMsg));
+
+  // 5) Check the behavior of ELFObjectFile<ELFT>::getSymbolType().
+  //    SymbolRef::getType() calls it internally. We can't test it directly,
+  //    because it is protected.
+  EXPECT_THAT_ERROR(BrokenSym.getType().takeError(), FailedWithMessage(ErrMsg));
+
+  // 6) Check the behavior of ELFObjectFile<ELFT>::getSymbolAddress().
+  //    SymbolRef::getAddress() calls it internally. We can't test it directly,
+  //    because it is protected.
+  EXPECT_THAT_ERROR(BrokenSym.getAddress().takeError(),
+                    FailedWithMessage(ErrMsg));
+
+  // Finally, check the `ELFFile<ELFT>::getEntry` API. This is an underlying
+  // method that generates errors for all cases above.
+  EXPECT_THAT_EXPECTED(Elf.getEntry<typename ELF64LE::Sym>(**SymtabSecOrErr, 0),
+                       Succeeded());
+  EXPECT_THAT_ERROR(
+      Elf.getEntry<typename ELF64LE::Sym>(**SymtabSecOrErr, BrokenSymIndex)
+          .takeError(),
+      FailedWithMessage(ErrMsg));
+}