// Copyright 2025 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "src/compiler/__stack_chk_fail.h"

#include <lib/zircon-internal/unique-backtrace.h>

#include "src/__support/common.h"

extern "C" {

// Calls to this function are generated by the compiler automatically in
// various modes controlled by `-fstack-protector` and other related switches.
// These are usually on by default, the various options controlling what kinds
// of functions will be "protected" by extra code in their frame setup logic.
// The Fuchsia Compiler ABI provides a pointer-sized "stack guard" value (via
// the thread pointer as specified in <zircon/tls.h>), which is randomized at
// process startup.  The compiler reserves a slot at the edge of a "protected"
// function's stack frame, called the "stack canary".  It emits extra code in
// the function prologue to copy the stack guard value provided by the ABI into
// the stack canary slot in the new call frame.  Corresponding code in the
// function's epilogue then fetches the guard value via the ABI again and
// compares it to the stack canary.  If they don't match, the epilogue calls
// __stack_chk_fail so the corrupted function will never return.  This can be
// an important safety and security measure, because the return address may be
// stored on the stack nearby to the stack canary word--if the canary is
// corrupted, the return value may also be corrupted and perhaps exploited to
// hijack control flow.  (This is not a direct risk when either safe-stack or
// shadow-call-stack is in use.  When using safe-stack, the canary is on the
// unsafe stack while the return address is on the machine stack; when using
// shadow-call-stack, the canary is on the machine stack while the return
// address is on the shadow call stack.  But other kinds of corruption can be
// dangerous and possibly exploited, so early detection here is still valued
// for safety and security.)
LLVM_LIBC_FUNCTION_ATTR [[noreturn]] void __stack_chk_fail() {
  // If this is in a backtrace, it indicates that the calling function's stack
  // frame was corrupted sometime between entering that function and returning
  // from it.  This can happen via a buffer overrun in that function itself, or
  // in one of its previous callees; or via other kinds of memory corruption.
  CRASH_WITH_UNIQUE_BACKTRACE();
}

}  // extern "C"