[Lldb-commits] [PATCH] D146919: Fix Issue #61706

[LU Hongyi via Phabricator via lldb-commits]

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As described in #61706 <https://github.com/llvm/llvm-project/issues/61706>, the `ValueObjectChild::UpdateValue(...)` may underflow the unsigned `m_bitfield_bit_offset`.

This is due to that in `ValueObjectChild::UpdateValue(...)`, the moved `overhang_bytes` only considers the `bitfield_end - *type_bit_size`. However, under certain cases, the `m_bitfield_bit_offset` may not strictly aligned to `*type_bit_size`, e.g. 27 < 32.

This results 27 - 32 = -5 underflows the unsigned `uint8_t m_bitfield_bit_offset`.

This patch fixes this issue by setting the `overhang_bytes` to the smaller value between `bitfield_end - *type_bit_size` and `m_bitfield_bit_offset` to avoid underflow.

I am quite new to this community, any helps/guidance are much appreciated.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D146919

Files:
  lldb/source/Core/ValueObjectChild.cpp


Index: lldb/source/Core/ValueObjectChild.cpp
===================================================================
--- lldb/source/Core/ValueObjectChild.cpp
+++ lldb/source/Core/ValueObjectChild.cpp
@@ -170,6 +170,8 @@
               if (bitfield_end > *type_bit_size) {
                 uint64_t overhang_bytes =
                     (bitfield_end - *type_bit_size + 7) / 8;
+                if (overhang_bytes > m_bitfield_bit_offset / 8)
+                  overhang_bytes = m_bitfield_bit_offset / 8;
                 m_byte_offset += overhang_bytes;
                 m_bitfield_bit_offset -= overhang_bytes * 8;
               }


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