[Bug 2023424] [NEW] GCC 13 on Lunar exhibits AddressSanitizer/UndefinedBehaviorSanitizer bug that doesn't manifest elsewhere

[Edward Nolan]

Public bug reported:

When initializing a class with a data member with alignment
`__attribute__((aligned(64)))` and enabling both AddressSanitizer and
UndefinedBehaviorSanitizer, Ubuntu 23.04's version of g++,
13-20230320-1ubuntu1, triggers UndefinedBehaviorSanitizer warnings on
valid code.

One-liner reproduction:

```
docker run ubuntu:23.04 bash -c 'apt-get update && apt-get install -y g++-13 && echo "struct Packet { int a = 0; int b __attribute__((aligned(64))); }; int main() { Packet packet; }" > ./foo.cpp && g++-13 -fsanitize=address -fsanitize=undefined ./foo.cpp && ./a.out'
```

```
foo.cpp:1:8: runtime error: member access within misaligned address 0x7f535a800020 for type 'struct Packet', which requires 64 byte alignment
0x7f535a800020: note: pointer points here
 fe 7f 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00
              ^
```

This also occurs if a more recent version, 13.1.0-2ubuntu2~23.04, is
installed from the ubuntu-toolchain-r PPA:

```
docker run ubuntu:23.04 bash -c 'apt-get update && apt-get install -y software-properties-common && add-apt-repository ppa:ubuntu-toolchain-r/ppa && apt-get update && apt-get install -y g++-13 && echo "struct Packet { int a = 0; int b __attribute__((aligned(64))); }; int main() { Packet packet; }" > ./foo.cpp && g++-13 -fsanitize=address -fsanitize=undefined ./foo.cpp && ./a.out'
```

The issue does not manifest on Fedora:

```
docker run fedora:38 bash -c 'yum -y update && yum -y install g++ libasan libubsan && echo "struct Packet { int a = 0; int b __attribute__((aligned(64))); }; int main() { Packet packet; }" > ./foo.cpp && g++ -fsanitize=address -fsanitize=undefined ./foo.cpp && ./a.out'
```

Or on Compiler Explorer: https://godbolt.org/z/Ybr6cfEGj

I suspect that an Ubuntu GCC patch is introducing the bug.

** Affects: gcc-13 (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/2023424

Title:
  GCC 13 on Lunar exhibits AddressSanitizer/UndefinedBehaviorSanitizer
  bug that doesn't manifest elsewhere

Status in gcc-13 package in Ubuntu:
  New

Bug description:
  When initializing a class with a data member with alignment
  `__attribute__((aligned(64)))` and enabling both AddressSanitizer and
  UndefinedBehaviorSanitizer, Ubuntu 23.04's version of g++,
  13-20230320-1ubuntu1, triggers UndefinedBehaviorSanitizer warnings on
  valid code.

  One-liner reproduction:

  ```
  docker run ubuntu:23.04 bash -c 'apt-get update && apt-get install -y g++-13 && echo "struct Packet { int a = 0; int b __attribute__((aligned(64))); }; int main() { Packet packet; }" > ./foo.cpp && g++-13 -fsanitize=address -fsanitize=undefined ./foo.cpp && ./a.out'
  ```

  ```
  foo.cpp:1:8: runtime error: member access within misaligned address 0x7f535a800020 for type 'struct Packet', which requires 64 byte alignment
  0x7f535a800020: note: pointer points here
   fe 7f 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00
                ^
  ```

  This also occurs if a more recent version, 13.1.0-2ubuntu2~23.04, is
  installed from the ubuntu-toolchain-r PPA:

  ```
  docker run ubuntu:23.04 bash -c 'apt-get update && apt-get install -y software-properties-common && add-apt-repository ppa:ubuntu-toolchain-r/ppa && apt-get update && apt-get install -y g++-13 && echo "struct Packet { int a = 0; int b __attribute__((aligned(64))); }; int main() { Packet packet; }" > ./foo.cpp && g++-13 -fsanitize=address -fsanitize=undefined ./foo.cpp && ./a.out'
  ```

  The issue does not manifest on Fedora:

  ```
  docker run fedora:38 bash -c 'yum -y update && yum -y install g++ libasan libubsan && echo "struct Packet { int a = 0; int b __attribute__((aligned(64))); }; int main() { Packet packet; }" > ./foo.cpp && g++ -fsanitize=address -fsanitize=undefined ./foo.cpp && ./a.out'
  ```

  Or on Compiler Explorer: https://godbolt.org/z/Ybr6cfEGj

  I suspect that an Ubuntu GCC patch is introducing the bug.

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