[BTF] Fix BTFParserTest.cpp for unaligned access after D149058

[eddyz87]

Summary

Test bot reported an issue with unit tests for D149058 in [1]:

[==========] Running 1 test from 1 test suite.
[----------] Global test environment set-up.
[----------] 1 test from BTFParserTest
[ RUN      ] BTFParserTest.simpleCorrectInput
/b/sanitizer-x86_64-linux-fast/build/llvm-project/llvm/unittests/DebugInfo/BTF/BTFParserTest.cpp:141:33:
runtime error: upcast of misaligned address 0x7facce60411f for type 'llvm::SmallString<0>', which requires 8 byte alignment
0x7facce60411f: note: pointer points here
 64 00 00 00 37  41 60 ce ac 7f 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00
             ^
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior
/b/sanitizer-x86_64-linux-fast/build/llvm-project/llvm/unittests/DebugInfo/BTF/BTFParserTest.cpp:141:33

The issue is caused by attribute "packed" used for too many things:

#pragma pack(push, 1)
struct MockData1 {
  struct B {
    ...
  } BTF;
  struct E {
    ...
  } Ext;

  int BTFSectionLen = sizeof(BTF);
  int ExtSectionLen = sizeof(Ext);

  SmallString<0> Storage;
  std::unique_ptr<ObjectFile> Obj;

}
#pragma pack(pop)

Access to unaligned pointers in Storage/Obj causes unaligned
access errors.

To fix this #pragma directives are pushed invards to apply only to B
and E definitions.

[1] https://lab.llvm.org/buildbot/#/builders/5/builds/35040

[luporl]

I've tested this patch and it also fixes unit tests for this ARM bot:
https://lab.llvm.org/buildbot/#/builders/245/builds/10973

[eddyz87]

Hi @luporl,

In D155176#4497053, @luporl wrote:

I've tested this patch and it also fixes unit tests for this ARM bot:
https://lab.llvm.org/buildbot/#/builders/245/builds/10973

Thank you for testing it, the pre-merge build also finished green. May I ask you to be a formal reviewer?
@MaskRay agreed with these changes here.

[luporl]

LGTM, thanks for the fix.

[MaskRay]

LGTM

llvm/unittests/DebugInfo/BTF/BTFParserTest.cpp

 // The yaml::yaml2ObjectFile() is used to generate actual ELF,
 // see MockData1::makeObj().
 //
 // The `BTF` and `Ext` fields are initialized with correct values
 // valid for a small example with a few sections, fields could be
 // modified before a call to `makeObj()` to test parser with invalid
 // input, etc.
 
+struct MockData1 {
 // Use "pragma pack" to model .BTF & .BTF.ext sections content using
 // 'struct' objects. This pragma is supported by CLANG, GCC & MSVC,
 // which matters for LLVM CI.
 #pragma pack(push, 1)
-struct MockData1 {
   struct B {
     BTF::Header Header = {};
     // no types
     struct S {
       char Foo[4] = "foo";
       char Bar[4] = "bar";
       char Buz[4] = "buz";
       char Line1[11] = "first line";
struct E {
     E() {
       Header.Magic = BTF::MAGIC;
       Header.Version = 1;
       Header.HdrLen = sizeof(Header);
       Header.LineInfoOff = offsetof(E, Lines) - sizeof(Header);
       Header.LineInfoLen = sizeof(Lines);
     }
   } Ext;
+#pragma pack(pop)
 
   int BTFSectionLen = sizeof(BTF);
   int ExtSectionLen = sizeof(Ext);
 
   SmallString<0> Storage;
   std::unique_ptr<ObjectFile> Obj;
 
   ObjectFile &makeObj() {
- Name:     .BTF.ext
     Content: )"
            << makeBinRef(&Ext, ExtSectionLen);
 
     Obj = yaml::yaml2ObjectFile(Storage, Buffer,
                                 [](const Twine &Err) { errs() << Err; });
     return *Obj.get();
   }
 };
-#pragma pack(pop)
 
 TEST(BTFParserTest, simpleCorrectInput) {
   BTFParser BTF;
   MockData1 Mock;
   Error Err = BTF.parse(Mock.makeObj());
   EXPECT_FALSE(Err);
 
   EXPECT_EQ(BTF.findString(offsetof(MockData1::B::S, Foo)), "foo");