[Lldb-commits] [PATCH] D73860: [lldb/StringPrinter] Avoid reading garbage in uninitialized strings

[Vedant Kumar via Phabricator via lldb-commits]

vsk added inline comments.


================
Comment at: lldb/source/DataFormatters/StringPrinter.cpp:144
+    return retval;
+  if (!llvm::checkedAdd(reinterpret_cast<intptr_t>(buffer),
+                        static_cast<intptr_t>(utf8_encoded_len)))
----------------
shafik wrote:
> Wouldn't we want `checkedAddUnsigned`? This would also mean casting to `uintptr_t`.
Not sure about that, as a change in the MSB seems significant to me.

Stepping back a bit though, it seems like this overflow check isn't useful. The data formatter must have called `GetPointeeData` to transfer the string payload into a host buffer, and we validate the number of bytes read against the size of the payload. So, if pointer overflow occurs, the `bytes_read` validation would catch it.

I'll just delete this.


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Comment at: lldb/source/DataFormatters/StringPrinter.cpp:474
       uint8_t *next_data = nullptr;
       auto printable = escaping_callback(data, data_end, next_data);
       auto printable_bytes = printable.GetBytes();
----------------
shafik wrote:
> Not your code but these `auto` seem unnecessary.  Especially `printable` is that just a `bool`?  Same comment in similar code above.
I'll leave this as a follow-up. `printable` is a `StringPrinter::StringPrinterBufferPointer`.


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Comment at: lldb/source/Plugins/Language/CPlusPlus/LibCxx.cpp:530
+
+    // When the small-string optimization takes place, the data must fit in the
+    // inline string buffer (23 bytes on x86_64/Darwin). If it doesn't, it's
----------------
shafik wrote:
> So `short_mode` means SSO? 
Yes.


================
Comment at: lldb/source/Plugins/Language/CPlusPlus/LibCxx.cpp:555
+    size = size_vo->GetValueAsUnsigned(LLDB_INVALID_OFFSET);
+    const uint64_t cap = cap_vo->GetValueAsUnsigned(LLDB_INVALID_OFFSET);
+    if (size == LLDB_INVALID_OFFSET || cap == LLDB_INVALID_OFFSET || cap < size)
----------------
shafik wrote:
> What does `cap` represent? It is not obvious in this context.
"capacity". I'm using the same jargon as the comment above `LibcxxStringLayoutMode` does, but it doesn't hurt to write this out.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D73860/new/

https://reviews.llvm.org/D73860