[llvm] [GSYM] Add support for querying merged functions in llvm-gsymutil (PR #120991)

[Greg Clayton via llvm-commits]

================
@@ -32,22 +32,59 @@ llvm::Error MergedFunctionsInfo::encode(FileWriter &Out) const {
   return Error::success();
 }
 
-llvm::Expected<MergedFunctionsInfo>
-MergedFunctionsInfo::decode(DataExtractor &Data, uint64_t BaseAddr) {
-  MergedFunctionsInfo MFI;
+llvm::Expected<std::vector<DataExtractor>>
+MergedFunctionsInfo::getFuncsDataExtractors(DataExtractor &Data) {
+  std::vector<DataExtractor> Results;
   uint64_t Offset = 0;
+
+  // Ensure there is enough data to read the function count.
+  if (!Data.isValidOffsetForDataOfSize(Offset, 4))
+    return createStringError(
+        std::errc::io_error,
+        "unable to read the function count at offset 0x%8.8" PRIx64, Offset);
+
   uint32_t Count = Data.getU32(&Offset);
 
   for (uint32_t i = 0; i < Count; ++i) {
+    // Ensure there is enough data to read the function size.
+    if (!Data.isValidOffsetForDataOfSize(Offset, 4))
+      return createStringError(
+          std::errc::io_error,
+          "unable to read size of function %u at offset 0x%8.8" PRIx64, i,
+          Offset);
+
     uint32_t FnSize = Data.getU32(&Offset);
-    DataExtractor FnData(Data.getData().substr(Offset, FnSize),
+
+    // Ensure there is enough data for the function content.
+    if (!Data.isValidOffsetForDataOfSize(Offset, FnSize))
+      return createStringError(
+          std::errc::io_error,
+          "function data is truncated for function %u at offset 0x%8.8" PRIx64
+          ", expected size %u",
+          i, Offset, FnSize);
+
+    // Extract the function data.
+    Results.emplace_back(Data.getData().substr(Offset, FnSize),
                          Data.isLittleEndian(), Data.getAddressSize());
-    llvm::Expected<FunctionInfo> FI =
-        FunctionInfo::decode(FnData, BaseAddr + Offset);
+
+    Offset += FnSize;
+  }
+  return Results;
+}
+
+llvm::Expected<MergedFunctionsInfo>
+MergedFunctionsInfo::decode(DataExtractor &Data, uint64_t BaseAddr) {
+  MergedFunctionsInfo MFI;
+  auto FuncExtractorsOrError = MFI.getFuncsDataExtractors(Data);
+
+  if (!FuncExtractorsOrError)
+    return FuncExtractorsOrError.takeError();
+
+  for (DataExtractor &FuncData : *FuncExtractorsOrError) {
+    llvm::Expected<FunctionInfo> FI = FunctionInfo::decode(FuncData, BaseAddr);
----------------
clayborg wrote:

move this above `MergedFunctionsInfo::getFuncsDataExtractors` to reduce merge issues.

https://github.com/llvm/llvm-project/pull/120991