llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT--> @llvm/pr-subscribers-compiler-rt-sanitizer Author: None (gbMattN) <details> <summary>Changes</summary> …ffset pointer This problem and fix was originally raised on Phabricator, https://reviews.llvm.org/D116861, by belkiss. I wasn't able to find them on github or the discourse so I'm re-raising this. The problem was reported as follows > I found that ubsan will report an incorrect alignment for a type in case it is allocated with the global operator new (without alignment), if we have it return an offset ptr. > > I wrote a small repro: https://godbolt.org/z/n8Yh8eoaE > > The type is aligned on 8 bytes (verified by static_assert on its alignof), but ubsan reports: "constructor call on misaligned address 0x000002af8fd8 for type 'Param', which requires 16 byte alignment". --- Full diff: https://github.com/llvm/llvm-project/pull/152532.diff 2 Files Affected: - (modified) clang/lib/CodeGen/CGExprCXX.cpp (+1-1) - (added) compiler-rt/test/ubsan/TestCases/global-new-alignment.cpp (+32) ``````````diff diff --git a/clang/lib/CodeGen/CGExprCXX.cpp b/clang/lib/CodeGen/CGExprCXX.cpp index c7e53331fe05f..ecc71a6343fd6 100644 --- a/clang/lib/CodeGen/CGExprCXX.cpp +++ b/clang/lib/CodeGen/CGExprCXX.cpp @@ -1798,7 +1798,7 @@ llvm::Value *CodeGenFunction::EmitCXXNewExpr(const CXXNewExpr *E) { SkippedChecks.set(SanitizerKind::Null, nullCheck); EmitTypeCheck(CodeGenFunction::TCK_ConstructorCall, E->getAllocatedTypeSourceInfo()->getTypeLoc().getBeginLoc(), - result, allocType, result.getAlignment(), SkippedChecks, + result, allocType, allocAlign, SkippedChecks, numElements); EmitNewInitializer(*this, E, allocType, elementTy, result, numElements, diff --git a/compiler-rt/test/ubsan/TestCases/global-new-alignment.cpp b/compiler-rt/test/ubsan/TestCases/global-new-alignment.cpp new file mode 100644 index 0000000000000..4586a0932affd --- /dev/null +++ b/compiler-rt/test/ubsan/TestCases/global-new-alignment.cpp @@ -0,0 +1,32 @@ +// RUN: %clangxx -fsanitize=alignment %s -o %t +// RUN: %run %t 2>&1 | FileCheck %s --implicit-check-not="runtime error" -allow-empty +// Disable with msan and tsan because they also override global new +// UNSUPPORTED: ubsan-msan, ubsan-tsan + +#include <cassert> +#include <cstddef> +#include <cstdlib> + +void *operator new(std::size_t count) { + constexpr const size_t offset = 8; + + // allocate a bit more so we can safely offset it + void *ptr = std::malloc(count + offset); + + // verify malloc returned 16 bytes aligned mem + static_assert(__STDCPP_DEFAULT_NEW_ALIGNMENT__ == 16, + "Global new doesn't return 16 bytes aligned memory!"); + assert((reinterpret_cast<std::ptrdiff_t>(ptr) & + (__STDCPP_DEFAULT_NEW_ALIGNMENT__ - 1)) == 0); + + return static_cast<char *>(ptr) + offset; +} + +struct Param { + void *_cookie1; + void *_cookie2; +}; + +static_assert(alignof(Param) == 8, "Param struct alignment must be 8 bytes!"); + +int main() { Param *p = new Param; } `````````` </details> https://github.com/llvm/llvm-project/pull/152532 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
