Remove nonnull attribute from sax_parse to prevent null check elision (#5048)#5089
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Nicolas0315 wants to merge 1 commit intonlohmann:developfrom
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Remove nonnull attribute from sax_parse to prevent null check elision (#5048)#5089Nicolas0315 wants to merge 1 commit intonlohmann:developfrom
Nicolas0315 wants to merge 1 commit intonlohmann:developfrom
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Clang with -O2 and -DNDEBUG optimizes away the 'sax == nullptr' safety check in sax_parse() because the parameter is annotated with JSON_HEDLEY_NON_NULL. This makes the compiler assume nullptr is never passed, allowing it to eliminate the check entirely. The result is a segfault instead of a proper exception. The existing #pragma workaround only suppresses the compiler warning but does not prevent the optimization. Remove JSON_HEDLEY_NON_NULL from all three sax_parse overloads (and the corresponding diagnostic pragmas that are no longer needed) in both include/ and single_include/ headers. Fixes nlohmann#5048
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As described in #5048: Anyway, the non null is the important part. The exception is just a minor safety net. If anything should be removed, it's that, imho. |
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Summary
Remove
JSON_HEDLEY_NON_NULLfrom all threesax_parse()overloads to prevent the compiler from optimizing away the null safety check.Problem
sax_parse()has a runtime null check:But the parameter is also annotated with
JSON_HEDLEY_NON_NULL, which expands to__attribute__((__nonnull__)). This tells the compiler that null is never passed, allowing it to eliminate the null check entirely in optimized builds (-O2 -DNDEBUG).Result: instead of a proper exception, users get a segfault.
The existing
#pragma diagnosticworkaround only suppresses the warning — it does not prevent the optimization.Fix
JSON_HEDLEY_NON_NULLfrom all threesax_parseoverloads#pragma clang/GCC diagnosticblocks around the null checksinclude/nlohmann/json.hppandsingle_include/nlohmann/json.hppThe null check is the correct safety mechanism. The
nonnullattribute contradicts it.Testing
Compiles cleanly with
clang++ -std=c++11 -O2 -DNDEBUG.Fixes #5048