Symbol.cc and FileStream.cc: Fix -Wconversion and -Wuseless-cast on 32-bit builds#3433
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…2-bit builds Symbol.cc: it - rs.begin() returns a value of type std::ptrdiff_t. On 32-bit systems, this is typically int, so casting it to int is redundant and triggers -Wuseless-cast. FileStream.cc: size_t is 32-bit on 32-bit systems, while position is int64_t. Casting int64_t to size_t can lead to truncation, causing -Wconversion errors. The fix ensures that the offset and position are checked to be non-negative before conversion. Fix: lib32-avro-c++/1.12/sources/avro-c++-1.12/lang/c++/impl/parsing/Symbol.cc:91:27: error: useless cast to type 'int' [-Werror=useless-cast] 91 | adj.push_back(static_cast<int>(it - rs.begin())); | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ cc1plus: all warnings being treated as errors lib32-avro-c++/1.12/sources/avro-c++-1.12/lang/c++/impl/FileStream.cc:208:41: error: conversion from 'int64_t'{aka 'long long int'} to 'size_t'{aka 'unsigned int'} may change value [-Werror=conversion] 208 | in_->seek(position - byteCount_ - available_); | ~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~ lib32-avro-c++/1.12/sources/avro-c++-1.12/lang/c++/impl/FileStream.cc:209:22: error: conversion from 'int64_t'{aka 'long long int'} to 'size_t'{aka 'unsigned int'} may change value [-Werror=conversion] 209 | byteCount_ = position; | ^~~~~~~~ cc1plus: all warnings being treated as errors These changes fix build failures on 32-bit systems and ensure safe type conversions. Signed-off-by: Alper Ak <[email protected]>
KalleOlaviNiemitalo commented Jul 16, 2025
Does Avro itself enable I doubt that warning will reveal any actual bug, so my first inclination would be to disable it altogether. But I'm not using the Avro C++ library so my opinion shouldn't have much weight here. |
alperak commented Jul 16, 2025
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kraj commented Jul 20, 2025
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Pull Request Overview
This PR fixes compiler warnings (-Wconversion and -Wuseless-cast) that occur when building on 32-bit systems. The changes ensure type-safe conversions between platform-dependent types.
Key Changes:
- Added compile-time type checking in Symbol.cc to avoid useless casts on 32-bit systems
- Added validation and explicit casts in FileStream.cc to prevent unsafe int64_t to size_t conversions
Reviewed Changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.
| File | Description |
|---|---|
| lang/c++/impl/parsing/Symbol.cc | Uses if constexpr to conditionally cast based on platform type |
| lang/c++/impl/FileStream.cc | Adds negative value checks and explicit casts for seek operations |
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| int64_t offset = position - static_cast<int64_t>(byteCount_) - static_cast<int64_t>(available_); | ||
| if (offset < 0){ | ||
| throwException("Negative offset in seek"); | ||
| } | ||
| in_->seek(static_cast<size_t>(offset)); | ||
| if (position < 0){ | ||
| throwException("Negative position not allowed"); | ||
| } |
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The negative offset check occurs after the subtraction, which means if position is less than byteCount_ + available_, a negative offset will be computed and then converted to a very large size_t value when cast on line 212. The check should occur before the cast, but the cast happens inside the function call. Consider restructuring to avoid passing a potentially negative value through the cast, or ensure the arithmetic cannot produce negative results through earlier validation.
| int64_t offset = position - static_cast<int64_t>(byteCount_) - static_cast<int64_t>(available_); | |
| if (offset < 0){ | |
| throwException("Negative offset in seek"); | |
| } | |
| in_->seek(static_cast<size_t>(offset)); | |
| if (position < 0){ | |
| throwException("Negative position not allowed"); | |
| } | |
| if (position < 0){ | |
| throwException("Negative position not allowed"); | |
| } | |
| int64_t offset = position - static_cast<int64_t>(byteCount_) - static_cast<int64_t>(available_); | |
| if (offset < 0){ | |
| throwException("Negative offset in seek"); | |
| } | |
| in_->seek(static_cast<size_t>(offset)); |
| if (position < 0){ | ||
| throwException("Negative position not allowed"); | ||
| } |
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The negative position check should occur at the beginning of the function, before any calculations are performed with position. Moving this validation earlier would fail fast and avoid unnecessary computation.
| if (offset < 0){ | ||
| throwException("Negative offset in seek"); | ||
| } | ||
| in_->seek(static_cast<size_t>(offset)); |
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Do we care about 32-bit systems ?
Update: Actually this PR is specifically for improving the things on 32bit systems.
The cast from int64_t to size_t may truncate on 32bit
| if (position < 0){ | ||
| throwException("Negative position not allowed"); | ||
| } | ||
| byteCount_ = static_cast<size_t>(position); |
| } else{ | ||
| adj.push_back(static_cast<int>(it - rs.begin())); | ||
| auto index = it - rs.begin(); | ||
| ifconstexpr (std::is_same_v<decltype(index), int>){ |
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Need to import <type_traits> for is_same_v ?
4 participants
Symbol.cc:
it - rs.begin() returns a value of type std::ptrdiff_t. On 32-bit systems, this is typically int, so casting it to int is redundant and triggers -Wuseless-cast.
FileStream.cc:
size_t is 32-bit on 32-bit systems, while position is int64_t. Casting int64_t to size_t can lead to truncation, causing -Wconversion errors. The fix ensures that the offset and position are checked to be non-negative before conversion.
Fix:
lib32-avro-c++/1.12/sources/avro-c++-1.12/lang/c++/impl/parsing/Symbol.cc:91:27: error: useless cast to type 'int' [-Werror=useless-cast]
91 | adj.push_back(static_cast(it - rs.begin()));
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1plus: all warnings being treated as errors
lib32-avro-c++/1.12/sources/avro-c++-1.12/lang/c++/impl/FileStream.cc:208:41: error: conversion from 'int64_t'{aka 'long long int'} to 'size_t'{aka 'unsigned int'} may change value [-Werror=conversion]
208 | in_->seek(position - byteCount_ - available_);
| ~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~
lib32-avro-c++/1.12/sources/avro-c++-1.12/lang/c++/impl/FileStream.cc:209:22:
error: conversion from 'int64_t'{aka 'long long int'} to 'size_t'
{aka 'unsigned int'} may change value [-Werror=conversion]
209 | byteCount_ = position;
| ^~~~~~~~
cc1plus: all warnings being treated as errors
These changes fix build failures on 32-bit systems and ensure safe type conversions.