[Lldb-commits] [lldb] [lldb] Set default object format to `MachO` in `ObjectFileMachO` (PR #142704)

[via lldb-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-lldb

Author: None (royitaqi)

<details>
<summary>Changes</summary>

The fact that `ObjectFileMachO` can parse the object file means that it's an Mach-O format. So it should just be set set the default format, before going through the rest of the code, which looks at load commands like `LC_VERSION_MIN_*` and `LC_BUILD_VERSION`.

For **production usage** where Mach-O files have the said load commands, this patch won't change anything.
* **Important note**: It's not clear to me if there are legitimate production use cases where the Mach-O files don't have said load commands. If there is, then what should be their object format? Without this patch, they are currently `ELF`. With this patch, they will be `MachO`.

For **unit tests**, this patch will simplify the yaml data by not requiring the said load commands.

A unit test is added to verify the patch, i.e. it fails without the patch and succeeds with.

```
$ ninja lldb-unit-test-deps
$ tools/lldb/unittests/ObjectFile/MachO/ObjectFileMachOTests --gtest_filter="*ObjectFileFormatWithoutLoadCommand*"
[==========] Running 1 test from 1 test suite.
...
[ RUN      ] ObjectFileMachOTest.ObjectFileFormatWithoutLoadCommand
[       OK ] ObjectFileMachOTest.ObjectFileFormatWithoutLoadCommand (3 ms)
...
```

---
Full diff: https://github.com/llvm/llvm-project/pull/142704.diff


2 Files Affected:

- (modified) lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp (+1) 
- (modified) lldb/unittests/ObjectFile/MachO/TestObjectFileMachO.cpp (+55) 


``````````diff
diff --git a/lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp b/lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp
index 3950454b7c90e..0079672c5cbd0 100644
--- a/lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp
+++ b/lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp
@@ -5148,6 +5148,7 @@ void ObjectFileMachO::GetAllArchSpecs(const llvm::MachO::mach_header &header,
   llvm::Triple base_triple = base_arch.GetTriple();
   base_triple.setOS(llvm::Triple::UnknownOS);
   base_triple.setOSName(llvm::StringRef());
+  base_triple.setObjectFormat(llvm::Triple::MachO);
 
   if (header.filetype == MH_PRELOAD) {
     if (header.cputype == CPU_TYPE_ARM) {
diff --git a/lldb/unittests/ObjectFile/MachO/TestObjectFileMachO.cpp b/lldb/unittests/ObjectFile/MachO/TestObjectFileMachO.cpp
index 0ef2d0b85fd36..aab3e996343b3 100644
--- a/lldb/unittests/ObjectFile/MachO/TestObjectFileMachO.cpp
+++ b/lldb/unittests/ObjectFile/MachO/TestObjectFileMachO.cpp
@@ -94,4 +94,59 @@ TEST_F(ObjectFileMachOTest, IndirectSymbolsInTheSharedCache) {
   for (size_t i = 0; i < 10; i++)
     OF->ParseSymtab(symtab);
 }
+
+TEST_F(ObjectFileMachOTest, ObjectFileFormatWithoutLoadCommand) {
+  // A Mach-O file without the load command LC_BUILD_VERSION.
+  const char *yamldata = R"(
+--- !mach-o
+FileHeader:
+  magic:           0xFEEDFACF
+  cputype:         0x0100000C
+  cpusubtype:      0x00000000
+  filetype:        0x00000001
+  ncmds:           1
+  sizeofcmds:      152
+  flags:           0x00002000
+  reserved:        0x00000000
+LoadCommands:
+  - cmd:             LC_SEGMENT_64
+    cmdsize:         152
+    segname:         __TEXT
+    vmaddr:          0
+    vmsize:          4
+    fileoff:         184
+    filesize:        4
+    maxprot:         7
+    initprot:        7
+    nsects:          1
+    flags:           0
+    Sections:
+      - sectname:        __text
+        segname:         __TEXT
+        addr:            0x0000000000000000
+        content:         'AABBCCDD'
+        size:            4
+        offset:          184
+        align:           0
+        reloff:          0x00000000
+        nreloc:          0
+        flags:           0x80000400
+        reserved1:       0x00000000
+        reserved2:       0x00000000
+        reserved3:       0x00000000
+...
+)";
+
+  // Perform setup.
+  llvm::Expected<TestFile> file = TestFile::fromYaml(yamldata);
+  EXPECT_THAT_EXPECTED(file, llvm::Succeeded());
+  auto module_sp = std::make_shared<Module>(file->moduleSpec());
+  ASSERT_NE(module_sp, nullptr);
+  auto object_file = module_sp->GetObjectFile();
+  ASSERT_NE(object_file, nullptr);
+
+  // Verify that the object file is recognized as Mach-O.
+  ASSERT_EQ(object_file->GetArchitecture().GetTriple().getObjectFormat(),
+            llvm::Triple::MachO);
+}
 #endif

``````````

</details>


https://github.com/llvm/llvm-project/pull/142704