[libunwind] e57f0e9 - [libunwind] fix pc range condition check bug (#154902)

[via cfe-commits]

Author: Wu Yingcong
Date: 2025-09-01T09:15:52+08:00
New Revision: e57f0e928d7b92f536a646d8ba1c26916b09e67e

URL: https://github.com/llvm/llvm-project/commit/e57f0e928d7b92f536a646d8ba1c26916b09e67e
DIFF: https://github.com/llvm/llvm-project/commit/e57f0e928d7b92f536a646d8ba1c26916b09e67e.diff

LOG: [libunwind] fix pc range condition check bug (#154902)

There is an off-by-one error with current condition check for PC fallen
into the range or not. There is another check within libunwind that use
the correct checks in
https://github.com/llvm/llvm-project/blob/5050da7ba18fc876f80fbeaaca3564d3b4483bb8/libunwind/src/UnwindCursor.hpp#L2757
```
      if ((fdeInfo.pcStart <= pc) && (pc < fdeInfo.pcEnd))
```

Added: 
    libunwind/test/eh_frame_fde_pc_range.pass.cpp

Modified: 
    libunwind/src/DwarfParser.hpp

Removed: 
    


################################################################################
diff  --git a/libunwind/src/DwarfParser.hpp b/libunwind/src/DwarfParser.hpp
index 7e85025dd054d..25250e0810987 100644
--- a/libunwind/src/DwarfParser.hpp
+++ b/libunwind/src/DwarfParser.hpp
@@ -273,7 +273,7 @@ bool CFI_Parser<A>::findFDE(A &addressSpace, pint_t pc, pint_t ehSectionStart,
           pint_t pcRange = addressSpace.getEncodedP(
               p, nextCFI, cieInfo->pointerEncoding & 0x0F);
           // Test if pc is within the function this FDE covers.
-          if ((pcStart < pc) && (pc <= pcStart + pcRange)) {
+          if ((pcStart <= pc) && (pc < pcStart + pcRange)) {
             // parse rest of info
             fdeInfo->lsda = 0;
             // check for augmentation length

diff  --git a/libunwind/test/eh_frame_fde_pc_range.pass.cpp b/libunwind/test/eh_frame_fde_pc_range.pass.cpp
new file mode 100644
index 0000000000000..d8bcb3939913c
--- /dev/null
+++ b/libunwind/test/eh_frame_fde_pc_range.pass.cpp
@@ -0,0 +1,58 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// Manually marking the .eh_frame_hdr as DW_EH_PE_omit to make libunwind to do
+// the linear search.
+// Assuming the begining of the function is at the start of the FDE range.
+
+// clang-format off
+
+// REQUIRES: linux
+
+// TODO: Figure out why this fails with Memory Sanitizer.
+// XFAIL: msan
+
+// RUN: %{build}
+// RUN: objcopy --dump-section .eh_frame_hdr=%t_ehf_hdr.bin %t.exe
+// RUN: echo -ne '\xFF' | dd of=%t_ehf_hdr.bin bs=1 seek=2 count=2 conv=notrunc status=none 
+// RUN: objcopy --update-section .eh_frame_hdr=%t_ehf_hdr.bin %t.exe
+// RUN: %{exec} %t.exe
+
+// clang-format on
+
+#include <assert.h>
+#include <libunwind.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <unwind.h>
+
+void f() {
+  printf("123\n");
+  void *pc = __builtin_return_address(0);
+  void *fpc = (void *)&f;
+  void *fpc1 = (void *)((uintptr_t)fpc + 1);
+
+  struct dwarf_eh_bases bases;
+  const void *fde_pc = _Unwind_Find_FDE(pc, &bases);
+  const void *fde_fpc = _Unwind_Find_FDE(fpc, &bases);
+  const void *fde_fpc1 = _Unwind_Find_FDE(fpc1, &bases);
+  printf("fde_pc = %p\n", fde_pc);
+  printf("fde_fpc = %p\n", fde_fpc);
+  printf("fde_fpc1 = %p\n", fde_fpc1);
+  fflush(stdout);
+  assert(fde_pc != NULL);
+  assert(fde_fpc != NULL);
+  assert(fde_fpc1 != NULL);
+  assert(fde_fpc == fde_fpc1);
+}
+
+int main() {
+  f();
+  return 0;
+}