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[sanitizer_common] Implement address sanitizer on AIX: stack unwinding #138188

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@jakeegan jakeegan commented May 1, 2025

Implement unwind.h-based stack unwinding routines on AIX.

Issue: #138916

@jakeegan jakeegan changed the title [sanitizer_common] Implement address sanitizer on AIX: stack unwinding [sanitizer_common] Implement address sanitizer on AIX: stack unwinding (6/n) May 7, 2025
@jakeegan jakeegan marked this pull request as ready for review May 7, 2025 17:36
@jakeegan jakeegan requested a review from vitalybuka May 7, 2025 17:36
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llvmbot commented May 7, 2025

@llvm/pr-subscribers-compiler-rt-sanitizer

Author: Jake Egan (jakeegan)

Changes

Implement unwind.h-based stack unwinding routines on AIX.


Full diff: https://github.com/llvm/llvm-project/pull/138188.diff

2 Files Affected:

  • (modified) compiler-rt/lib/sanitizer_common/CMakeLists.txt (+1)
  • (added) compiler-rt/lib/sanitizer_common/sanitizer_unwind_aix.cpp (+66)
diff --git a/compiler-rt/lib/sanitizer_common/CMakeLists.txt b/compiler-rt/lib/sanitizer_common/CMakeLists.txt
index 6e6dfd2f33ebf..96c23c6d8ab82 100644
--- a/compiler-rt/lib/sanitizer_common/CMakeLists.txt
+++ b/compiler-rt/lib/sanitizer_common/CMakeLists.txt
@@ -97,6 +97,7 @@ set(SANITIZER_SYMBOLIZER_SOURCES
   sanitizer_symbolizer_report_fuchsia.cpp
   sanitizer_symbolizer_win.cpp
   sanitizer_thread_history.cpp
+  sanitizer_unwind_aix.cpp
   sanitizer_unwind_linux_libcdep.cpp
   sanitizer_unwind_fuchsia.cpp
   sanitizer_unwind_win.cpp
diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_unwind_aix.cpp b/compiler-rt/lib/sanitizer_common/sanitizer_unwind_aix.cpp
new file mode 100644
index 0000000000000..45b4b1f3d5c9d
--- /dev/null
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_unwind_aix.cpp
@@ -0,0 +1,66 @@
+//===-- sanitizer_unwind_aix.cpp ------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This file contains the unwind.h-based (aka "slow") stack unwinding routines
+// available to the tools on AIX.
+//===----------------------------------------------------------------------===//
+
+#include "sanitizer_platform.h"
+
+#if SANITIZER_AIX
+#  include <unwind.h>
+
+#  include "sanitizer_common.h"
+#  include "sanitizer_stacktrace.h"
+
+namespace __sanitizer {
+
+struct UnwindTraceArg {
+  BufferedStackTrace *stack;
+  u32 max_depth;
+};
+
+_Unwind_Reason_Code Unwind_Trace(struct _Unwind_Context *ctx, void *param) {
+  UnwindTraceArg *arg = (UnwindTraceArg *)param;
+  CHECK_LT(arg->stack->size, arg->max_depth);
+  uptr pc = _Unwind_GetIP(ctx);
+  // On AIX 32-bit and 64-bit, address smaller than 0x0fffffff is for kernel.
+  if (pc <= 0x0fffffff)
+    return _URC_NORMAL_STOP;
+  arg->stack->trace_buffer[arg->stack->size++] = pc;
+  if (arg->stack->size == arg->max_depth)
+    return _URC_NORMAL_STOP;
+  return _URC_NO_REASON;
+}
+
+void BufferedStackTrace::UnwindSlow(uptr pc, u32 max_depth) {
+  CHECK_GE(max_depth, 2);
+  size = 0;
+  UnwindTraceArg arg = {this, Min(max_depth + 1, kStackTraceMax)};
+  _Unwind_Backtrace(Unwind_Trace, &arg);
+  // We need to pop a few frames so that pc is on top.
+  uptr to_pop = LocatePcInTrace(pc);
+  // trace_buffer[0] belongs to the current function so we always pop it,
+  // unless there is only 1 frame in the stack trace (1 frame is always better
+  // than 0!).
+  // 1-frame stacks don't normally happen, but this depends on the actual
+  // unwinder implementation (libgcc, libunwind, etc) which is outside of our
+  // control.
+  if (to_pop == 0 && size > 1)
+    to_pop = 1;
+
+  PopStackFrames(to_pop);
+  trace_buffer[0] = pc;
+}
+
+void BufferedStackTrace::UnwindSlow(uptr pc, void *context, u32 max_depth) {
+  UnwindSlow(pc, max_depth);
+}
+}  // namespace __sanitizer
+
+#endif  // SANITIZER_AIX

u32 max_depth;
};

_Unwind_Reason_Code Unwind_Trace(struct _Unwind_Context *ctx, void *param) {
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I think this function can be static?

@jakeegan jakeegan changed the title [sanitizer_common] Implement address sanitizer on AIX: stack unwinding (6/n) [sanitizer_common] Implement address sanitizer on AIX: stack unwinding May 12, 2025
UnwindTraceArg *arg = (UnwindTraceArg *)param;
CHECK_LT(arg->stack->size, arg->max_depth);
uptr pc = _Unwind_GetIP(ctx);
// On AIX 32-bit and 64-bit, address smaller than 0x0fffffff is for kernel.
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Comment wording should match use of <= in the code.

Suggested change
// On AIX 32-bit and 64-bit, address smaller than 0x0fffffff is for kernel.
// On AIX 32-bit and 64-bit, addresses up through 0x0fffffff are for kernel.

}

void BufferedStackTrace::UnwindSlow(uptr pc, void *context, u32 max_depth) {
UnwindSlow(pc, max_depth);
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Let's enforce the interface preconditions even if they are currently harmless to ignore. This conveniently removes any possible warnings that context is unused.

Suggested change
UnwindSlow(pc, max_depth);
CHECK(context);
UnwindSlow(pc, max_depth);

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