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Fix two issues that undefined behavior sanitizer caught #419

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Fix two issues that undefined behavior sanitizer caught #419

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03396ce
fix(string): avoid undefined behavior when memcpy source is null
henrylhtsang Jan 19, 2026
2550deb
fix(object): use offsetof instead of null pointer arithmetic
henrylhtsang Jan 19, 2026
3cf3b41
gemini and __builtin_offsetof
henrylhtsang Jan 23, 2026
81a1cf9
remove #include <cstddef>
henrylhtsang Jan 23, 2026
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5 changes: 3 additions & 2 deletions include/tvm/ffi/object.h
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Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,7 @@
#include <tvm/ffi/base_details.h>
#include <tvm/ffi/c_api.h>

#include <cstddef>
#include <optional>
#include <string>
#include <type_traits>
Expand Down Expand Up @@ -1094,8 +1095,8 @@ struct ObjectUnsafe {

template <typename Class>
TVM_FFI_INLINE static int64_t GetObjectOffsetToSubclass() {
return (reinterpret_cast<int64_t>(&(static_cast<Class*>(nullptr)->header_)) -
reinterpret_cast<int64_t>(&(static_cast<Object*>(nullptr)->header_)));
return static_cast<int64_t>(offsetof(Class, header_)) -
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@tqchen tqchen Jan 21, 2026

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it is helpful to likely use __builtin_offsetof instead, mainly because it is more permissive per standard

static_cast<int64_t>(offsetof(Object, header_));
}

template <typename T>
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4 changes: 3 additions & 1 deletion include/tvm/ffi/string.h
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Expand Up @@ -754,7 +754,9 @@ class String {
}
void InitData(const char* data, size_t size) {
char* dest_data = InitSpaceForSize(size);
std::memcpy(dest_data, data, size);
if (size > 0) {
std::memcpy(dest_data, data, size);
}
Comment on lines +759 to +761
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@gemini-code-assist gemini-code-assist bot Jan 20, 2026

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high

This is a great fix to prevent undefined behavior when memcpy is called with a size of 0 and a null source pointer. I noticed that the Bytes::InitData method in this same file has a similar implementation without this check. It would be beneficial to apply the same fix there to ensure consistency and prevent the same undefined behavior in the Bytes class.

dest_data[size] = '\0';
}
/*!
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