[Lldb-commits] [lldb] [lldb] Limit formatter-section extractor range (PR #140139)

[via lldb-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-lldb

Author: nerix (Nerixyz)

<details>
<summary>Changes</summary>

The formatter extraction would look at too much data for one type.
This PR limits the size of the `DataExtractor` to the one specified in the 
record size before - previously, the whole section was looked at.
Similarly, `ForEachFormatterInModule` skipped zero-bytes but didn't stop when 
reaching the end of the extractor.

I hit both cases in an even smaller test than the one currently in the repo, 
but I tried this on Windows[^1]. In my executable, the formatter section 
started with my specified formatter and was padded to 512 bytes with zeroes.
I'd guess this should've come up in the existing test case, so macOS might do 
something different here[?].

&lt;details&gt;&lt;summary&gt;Test File&lt;/summary&gt;

```c
struct Point {
  int x;
  int y;
};

__attribute__((used, section(".lldbformatters"))) const char my_string[] = {
    0x01, // version
    0x12, // record size
    0x05, // type size
    'P',  'o', 'i', 'n', 't',
    0x00, // flags
    0x00, // signature
    0x09, // byte-code length
    0x01, // drop
    0x22, // push str
    0x05, // str len
    'A',  'A', 'A', 'A', 'A',
    0x13, // return
};

int main() {
  Point a{3, 4};
  return a.x + a.y; // break here
}
```
&lt;/details&gt; 

[^1]: I had to change the section name matching to use an 8 byte name in the 
[PE/COFF](https://github.com/llvm/llvm-project/blob/acdba28e148ac1e94d6c041f9911230e1e90e9cd/lldb/source/Plugins/ObjectFile/PECOFF/ObjectFilePECOFF.cpp#L1003)
 reader, since executables on Windows [can't have section names longer than 8 
bytes](https://learn.microsoft.com/en-us/windows/win32/debug/pe-format#section-table-section-headers)
 (actually they can, and in MinGW they do, but I couldn't get `clang-cl` to 
generate such a binary).

---
Full diff: https://github.com/llvm/llvm-project/pull/140139.diff


1 Files Affected:

- (modified) lldb/source/DataFormatters/FormatterSection.cpp (+6-2) 


``````````diff
diff --git a/lldb/source/DataFormatters/FormatterSection.cpp 
b/lldb/source/DataFormatters/FormatterSection.cpp
index 1de633f4998e0..72979ac1923e8 100644
--- a/lldb/source/DataFormatters/FormatterSection.cpp
+++ b/lldb/source/DataFormatters/FormatterSection.cpp
@@ -57,11 +57,15 @@ static void ForEachFormatterInModule(
       cursor.seek(cursor.tell() - 1);
       break;
     }
+    if (!cursor || cursor.tell() >= section_size)
+      break;
+
     uint64_t version = section.getULEB128(cursor);
     uint64_t record_size = section.getULEB128(cursor);
     if (version == 1) {
-      llvm::DataExtractor record(section.getData().drop_front(cursor.tell()),
-                                 le, addr_size);
+      llvm::DataExtractor record(
+          section.getData().drop_front(cursor.tell()).take_front(record_size),
+          le, addr_size);
       llvm::DataExtractor::Cursor cursor(0);
       uint64_t type_size = record.getULEB128(cursor);
       llvm::StringRef type_name = record.getBytes(cursor, type_size);

``````````

</details>


https://github.com/llvm/llvm-project/pull/140139
_______________________________________________
lldb-commits mailing list
lldb-commits@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-commits