llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT--> @llvm/pr-subscribers-clang Author: Jann (thejh) <details> <summary>Changes</summary> Attr.td names the first alloc_size argument "ElemSizeParam" and the second optional argument "NumElemsParam"; but the semantics of how the two-argument version is used in practice is the opposite of that. glibc declares calloc() like this, so the second alloc_size argument is the element size: ``` extern void *calloc (size_t __nmemb, size_t __size) __THROW __attribute_malloc__ __attribute_alloc_size__ ((1, 2)) __wur; ``` The Linux kernel declares array allocation functions like `kmalloc_array_noprof()` the same way. Add a comment explaining that the names used inside clang are misleading. --- Full diff: https://github.com/llvm/llvm-project/pull/134899.diff 1 Files Affected: - (modified) clang/include/clang/Basic/Attr.td (+7) ``````````diff diff --git a/clang/include/clang/Basic/Attr.td b/clang/include/clang/Basic/Attr.td index fd9e686485552..b7ad432738b29 100644 --- a/clang/include/clang/Basic/Attr.td +++ b/clang/include/clang/Basic/Attr.td @@ -1709,6 +1709,13 @@ def EmptyBases : InheritableAttr, TargetSpecificAttr<TargetMicrosoftCXXABI> { def AllocSize : InheritableAttr { let Spellings = [GCC<"alloc_size">]; let Subjects = SubjectList<[HasFunctionProto]>; + // The parameter names here are a bit misleading. + // When used with a single argument, the first argument is obviously the + // allocation size; but when used with two arguments, the first argument is + // usually the number of elements, while the second argument is usually the + // element size - the reverse of how they are named here. + // The documentation of both GCC and clang does not describe any semantic + // difference between the first and second argument. let Args = [ParamIdxArgument<"ElemSizeParam">, ParamIdxArgument<"NumElemsParam", /*opt*/ 1>]; let TemplateDependent = 1; `````````` </details> https://github.com/llvm/llvm-project/pull/134899 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
