[clang] [llvm] Reland: [llvm][clang] Allocate a new stack instead of spawning a new thread to get more stack space (PR #136046)

[Michael Spencer via cfe-commits]

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@@ -0,0 +1,127 @@
+//===--- RunOnNewStack.cpp - Crash Recovery -------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Support/ProgramStack.h"
+#include "llvm/Config/config.h"
+#include "llvm/Support/Compiler.h"
+
+#ifdef LLVM_ON_UNIX
+# include <sys/resource.h> // for getrlimit
+#endif
+
+#ifdef _MSC_VER
+# include <intrin.h>  // for _AddressOfReturnAddress
+#endif
+
+#ifndef LLVM_HAS_SPLIT_STACKS
+# include "llvm/Support/thread.h"
+#endif
+
+using namespace llvm;
+
+uintptr_t llvm::getStackPointer() {
+#if __GNUC__ || __has_builtin(__builtin_frame_address)
+  return (uintptr_t)__builtin_frame_address(0);
+#elif defined(_MSC_VER)
+  return (uintptr_t)_AddressOfReturnAddress();
+#else
+  volatile char CharOnStack = 0;
+  // The volatile store here is intended to escape the local variable, to
+  // prevent the compiler from optimizing CharOnStack into anything other
+  // than a char on the stack.
+  //
+  // Tested on: MSVC 2015 - 2019, GCC 4.9 - 9, Clang 3.2 - 9, ICC 13 - 19.
+  char *volatile Ptr = &CharOnStack;
+  return (uintptr_t)Ptr;
+#endif
+}
+
+unsigned llvm::getDefaultStackSize() {
+#ifdef LLVM_ON_UNIX
+  rlimit RL;
+  getrlimit(RLIMIT_STACK, &RL);
+  return RL.rlim_cur;
+#else
+  // Clang recursively parses, instantiates templates, and evaluates constant
+  // expressions. We've found 8MiB to be a reasonable stack size given the way
+  // Clang works and the way C++ is commonly written.
+  return 8 << 20;
+#endif
+}
+
+// Not an anonymous namespace to avoid warning about undefined local function.
+namespace llvm {
+#ifdef LLVM_HAS_SPLIT_STACKS_AARCH64
+void runOnNewStackImpl(void *Stack, void (*Fn)(void *), void *Ctx) __asm__(
+    "_ZN4llvm17runOnNewStackImplEPvPFvS0_ES0_");
+
+// This can't use naked functions because there is no way to know if cfi
+// directives are being emitted or not.
+//
+// When adding new platforms it may be better to move to a .S file with macros
+// for dealing with platform differences.
+__asm__ (
+    ".globl  _ZN4llvm17runOnNewStackImplEPvPFvS0_ES0_\n\t"
+    ".p2align  2\n\t"
+    "_ZN4llvm17runOnNewStackImplEPvPFvS0_ES0_:\n\t"
+    ".cfi_startproc\n\t"
+    "mov       x16, sp\n\t"
+    "sub       x0, x0, #0x20\n\t"            // subtract space from stack
+    "stp       xzr, x16, [x0, #0x00]\n\t"    // save old sp
+    "stp       x29, x30, [x0, #0x10]\n\t"    // save fp, lr
+    "mov       sp, x0\n\t"                   // switch to new stack
+    "add       x29, x0, #0x10\n\t"           // switch to new frame
+    ".cfi_def_cfa w29, 16\n\t"
----------------
Bigcheese wrote:

The CFI info is about what `x29` points to, which is only valid after the assignment via `add`.  I verified that stopping lldb between the `mov sp, x0` and `add    x29, x0, #0x10` works.

https://github.com/llvm/llvm-project/pull/136046