add stack traces to pointer stability safety locks

[andrewrk]

Extracted from #17719.

Based on this comment by @GethDW: #17719 (comment)

Comment reproduced here:

I think it would be good to add a ConfigurableTrace and panic with it to quickly identify where it was locked. I'm not too familiar with StackTrace but I played around with it and got:

pub const SafetyLock = struct {
    state: State = .unlocked,
    trace: std.debug.ConfigurableTrace(2, 1, runtime_safety) = .{},

    pub const State = if (runtime_safety) enum { unlocked, locked } else enum { unlocked };

    pub fn lock(l: *SafetyLock) void {
        if (!runtime_safety) return;
        l.trace.addAddr(@returnAddress(), "locked");
        if (l.state == .locked) l.panic("locked while already locked");
        l.state = .locked;
    }

    pub fn unlock(l: *SafetyLock) void {
        if (!runtime_safety) return;
        l.trace.addAddr(@returnAddress(), "unlock");
        if (l.state == .unlocked) l.panic("unlocked while already unlocked");
        l.trace = .{};
        l.state = .unlocked;
    }

    pub fn assertUnlocked(l: *SafetyLock, comptime msg: []const u8, ret_addr: usize) void {
        if (!runtime_safety) return;
        l.trace.addAddr(ret_addr, msg);
        if (l.state != .unlocked) l.panic(msg);
    }

    fn panic(l: SafetyLock, comptime msg: []const u8) noreturn {
        var insts = [2]usize{ l.trace.addrs[0][0], l.trace.addrs[1][0] };
        const stack_trace = std.builtin.StackTrace{
            .index = l.trace.index,
            .instruction_addresses = &insts,
        };
        std.debug.panicImpl(&stack_trace, null, msg);
    }
};

The trace can then look like this:

thread 343239 panic: modified while locked
/home/gethin/random/test/src/main.zig:53:14: 0x21d788 in main (test)
    lock.lock(); // locked
             ^
/home/gethin/random/test/src/main.zig:54:11: 0x21d791 in main (test)
    modify(&lock); // modified
...

---

This issue is to evaluate whether enabling this unconditionally in debug mode is prohibitively expensive in terms of performance and memory, or not. And depending on the results of this investigation, potentially create a std lib configuration option for setting the number of stack trace frames to collect for safety locks.

Related:

• introduce pointer stability safety locks to array lists #19326
• introduce pointer stability safety locks to MultiArrayList #19327