reached unreachable code during capture stack trace

[andrewrk]

bd8ef00

test
+- test-modules
   +- test-std
      +- run test std-aarch64_be-linux.4.19...6.11.5-musl-generic-Debug-libc failure
thread 982114 panic: reached unreachable code
/home/ci/actions-runner5/_work/zig/zig/lib/std/posix.zig:1006:23: 0x1d7ef93 in pread (test)
            .INVAL => unreachable,
                      ^
/home/ci/actions-runner5/_work/zig/zig/lib/std/fs/File.zig:1204:23: 0x1d6fa1b in pread (test)
    return posix.pread(self.handle, buffer, offset);
                      ^
/home/ci/actions-runner5/_work/zig/zig/lib/std/debug/MemoryAccessor.zig:66:41: 0x1d4bdeb in read (test)
            else => return (ma.mem.pread(buf, address) catch return false) == buf.len,
                                        ^
/home/ci/actions-runner5/_work/zig/zig/lib/std/debug/MemoryAccessor.zig:77:23: 0x1d3cd9b in load__anon_14111 (test)
    return if (ma.read(address, std.mem.asBytes(&result))) result else null;
                      ^
/home/ci/actions-runner5/_work/zig/zig/lib/std/debug.zig:789:50: 0x1d1b89f in next_internal (test)
        const new_fp = math.add(usize, it.ma.load(usize, fp) orelse return null, fp_bias) catch
                                                 ^
/home/ci/actions-runner5/_work/zig/zig/lib/std/debug.zig:720:39: 0x1cfab6b in next (test)
        var address = it.next_internal() orelse return null;
                                      ^
/home/ci/actions-runner5/_work/zig/zig/lib/std/debug.zig:355:29: 0x1d00b03 in captureStackTrace (test)
            addr.* = it.next() orelse {
                            ^
/home/ci/actions-runner5/_work/zig/zig/lib/std/heap/general_purpose_allocator.zig:510:40: 0x1d2075b in collectStackTrace (test)
            std.debug.captureStackTrace(first_trace_addr, &stack_trace);
                                       ^
/home/ci/actions-runner5/_work/zig/zig/lib/std/heap/general_purpose_allocator.zig:309:34: 0x1d00e7f in captureStackTrace (test)
                collectStackTrace(ret_addr, stack_addresses);
                                 ^
/home/ci/actions-runner5/_work/zig/zig/lib/std/heap/general_purpose_allocator.zig:931:37: 0x1cddb7b in free (test)
            bucket.captureStackTrace(ret_addr, size_class, slot_index, .free);
                                    ^
/home/ci/actions-runner5/_work/zig/zig/lib/std/mem/Allocator.zig:98:28: 0x25e9617 in destroy__anon_228383 (test)
    return self.vtable.free(self.ptr, buf, log2_buf_align, ret_addr);
                           ^
/home/ci/actions-runner5/_work/zig/zig/lib/std/Thread/Pool.zig:236:43: 0x25e77d7 in runFn (test)
            closure.pool.allocator.destroy(closure);
                                          ^
/home/ci/actions-runner5/_work/zig/zig/lib/std/Thread/Pool.zig:291:32: 0x25ea5ff in worker (test)
            run_node.data.runFn(&run_node.data, id);
                               ^
/home/ci/actions-runner5/_work/zig/zig/lib/std/Thread.zig:486:13: 0x25e9a8b in callFn__anon_228428 (test)
            @call(.auto, f, args);
            ^
/home/ci/actions-runner5/_work/zig/zig/lib/std/Thread.zig:755:30: 0x25e9293 in entryFn (test)
                return callFn(f, args_ptr.*);
                             ^
/home/ci/actions-runner5/_work/zig/zig/lib/libc/musl/src/thread/pthread_create.c:207:17: 0x33426ff in start (/home/ci/actions-runner5/_work/zig/zig/lib/libc/musl/src/thread/pthread_create.c)
 __pthread_exit(args->start_func(args->start_arg));
                ^

I don't like this MemoryAccessor thing. It should be deleted so that collecting stack traces is faster and doesn't depend on accessing inaccessible memory.

[alexrp]

Already on this one. It's a random failure introduced in #21894. I'm hoping #21910 will fix it, and if not, I'll revert the offending commit.

[andrewrk]

Thanks. I still don't like that MemoryAccessor is being used during GPA allocation however. We had stack traces working fine before that API was introduced.

[mlugg]

This was resolved by #24960.