[llvm] [llvm][cmake] Try LLVM libunwind when frame registration is unavailable (PR #112087)

[via llvm-commits]

https://github.com/ziyao233 created https://github.com/llvm/llvm-project/pull/112087

Currently __register_frame and __unw_add_dynamic_fde are probed by default and OrcJIT prefers the later. But on a system with only LLVM libunwind available, we may need to link libunwind explicitly.

This patch tries to link LLVM libunwind if frame registeration is not available by default, preventing LLVM-built systems falling back to __register_frame code path. Such fallback leads to errors like

  $ clang-repl
  clang-repl> 1 + 1;
  libunwind: __unw_add_dynamic_fde: bad fde: FDE is really a CIE

because __register_frame's behavior differs between libgcc and LLVM libunwind.

>From 8fc98f215917d61ebdd7a52ebec2d3d423f6cc9c Mon Sep 17 00:00:00 2001
From: Yao Zi <ziyao at disroot.org>
Date: Fri, 11 Oct 2024 08:16:22 +0000
Subject: [PATCH] [llvm][cmake] Try LLVM libunwind when frame registration is
 unavailable

Currently __register_frame and __unw_add_dynamic_fde are probed by
default and OrcJIT prefers the later. But on a system with only LLVM
libunwind available, we may need to link libunwind explicitly.

This patch tries to link LLVM libunwind if frame registeration is not
available by default, preventing LLVM-built systems falling back to
__register_frame code path. Such fallback leads to errors like

  $ clang-repl
  clang-repl> 1 + 1;
  libunwind: __unw_add_dynamic_fde: bad fde: FDE is really a CIE

because __register_frame's behavior differs between libgcc and LLVM
libunwind.

Signed-off-by: Yao Zi <ziyao at disroot.org>
---
 llvm/cmake/config-ix.cmake | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/llvm/cmake/config-ix.cmake b/llvm/cmake/config-ix.cmake
index 86f2bac7d23e84..38d08f968ca9ea 100644
--- a/llvm/cmake/config-ix.cmake
+++ b/llvm/cmake/config-ix.cmake
@@ -272,6 +272,13 @@ endif()
 check_symbol_exists(__register_frame "${CMAKE_CURRENT_LIST_DIR}/unwind.h" HAVE_REGISTER_FRAME)
 check_symbol_exists(__deregister_frame "${CMAKE_CURRENT_LIST_DIR}/unwind.h" HAVE_DEREGISTER_FRAME)
 check_symbol_exists(__unw_add_dynamic_fde "${CMAKE_CURRENT_LIST_DIR}/unwind.h" HAVE_UNW_ADD_DYNAMIC_FDE)
+if (NOT (HAVE_REGISTER_FRAME OR HAVE_DEREGISTER_FRAME OR HAVE_UNW_ADD_DYNAMIC_FDE))
+  check_library_exists(unwind __unw_add_dynamic_fde "" HAVE_LLVM_LIBUNWIND)
+  if (HAVE_LLVM_LIBUNWIND)
+    list(APPEND CMAKE_REQUIRED_LIBRARIES "unwind")
+    set(HAVE_UNW_ADD_DYNAMIC_FDE 1)
+  endif ()
+endif ()
 
 check_symbol_exists(_Unwind_Backtrace "unwind.h" HAVE__UNWIND_BACKTRACE)
 check_symbol_exists(getpagesize unistd.h HAVE_GETPAGESIZE)