[llvm-bugs] [Bug 45144] New: __builtin_dump_struct buffer overrun with types it doesn't handle

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=45144

            Bug ID: 45144
           Summary: __builtin_dump_struct buffer overrun with types it
                    doesn't handle
           Product: clang
           Version: 9.0
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: C++
          Assignee: unassignedclangbugs at nondot.org
          Reporter: ndkrempel at gmail.com
                CC: blitzrakete at gmail.com, dgregor at apple.com,
                    erik.pilkington at gmail.com, llvm-bugs at lists.llvm.org,
                    richard-llvm at metafoo.co.uk

The following program:

#include <cstdio>
struct Foo {
    short a[1];
};
int main() {
    Foo f = {2};
    __builtin_dump_struct(&f, &std::printf);
}

prints out garbage data from clang's memory:

struct Foo {
short [1] a : 0x315b2074726f0002
}

The "0002" on the end is the valid data, the rest is presumably whatever
happened to be in the compiler's memory afterwards.

A similar thing happens with any field type that __builtin_dump_struct doesn't
understand - it prints out 8 bytes (or maybe 4 bytes on a 32-bit system) of
data, regardless of the actual size of the field.

Reproduced on clang 9.0.0 and trunk. Didn't seem to occur on 7.0.0 and 8.0.0
but that could have just been getting lucky that the extra bytes displayed were
all 0.

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