[libcxx-commits] [clang] [libcxx] [Clang] Diagnose forming references to nullptr (PR #143667)

[Nathan Chancellor via libcxx-commits]

nathanchance wrote:

I am seeing a new build failure when building the Linux kernel as a result of this change.

```
drivers/tty/sysrq.c:486:2: error: initializer element is not a compile-time constant
  486 |         &sysrq_showlocks_op,            /* d */
      |         ^~~~~~~~~~~~~~~~~~~
```

as a result of

```c
#ifdef CONFIG_LOCKDEP
static void sysrq_handle_showlocks(u8 key)
{
	debug_show_all_locks();
}

static const struct sysrq_key_op sysrq_showlocks_op = {
	.handler	= sysrq_handle_showlocks,
	.help_msg	= "show-all-locks(d)",
	.action_msg	= "Show Locks Held",
};
#else
#define sysrq_showlocks_op (*(const struct sysrq_key_op *)NULL)
#endif
```

This build does not have LOCKDEP enabled so `&sysrq_showlocks_op` becomes `&(*(const struct sysrq_key_op *)((void *)0))`. Is the error expected in this case? I am not sure if this construct is used elsewhere in the kernel but it was in the first build that was attempted during a compiler upgrade.

https://github.com/llvm/llvm-project/pull/143667