[flang][runtime] Make sure to link libexecinfo if it exists

[brad0]

Fixes building the backtrace support on FreeBSD/NetBSD/OpenBSD/DragonFly and musl
libc with libexecinfo.

[llvmbot]

@llvm/pr-subscribers-flang-runtime

Author: Brad Smith (brad0)

Changes

Fixes building the backtrace support on FreeBSD/NetBSD/OpenBSD/DragonFly and musl
libc with libexecinfo.

---

Full diff: https://github.com/llvm/llvm-project/pull/125344.diff

1 Files Affected:

• (modified) flang/runtime/CMakeLists.txt (+7-2)

diff --git a/flang/runtime/CMakeLists.txt b/flang/runtime/CMakeLists.txt
index fbfaae9a880648..bf27a121e4d174 100644
--- a/flang/runtime/CMakeLists.txt
+++ b/flang/runtime/CMakeLists.txt
@@ -59,10 +59,15 @@ if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
     )
 endif()
 
+set(linked_libraries FortranDecimal)
+
 # function checks
 find_package(Backtrace)
 set(HAVE_BACKTRACE ${Backtrace_FOUND})
 set(BACKTRACE_HEADER ${Backtrace_HEADER})
+if(HAVE_BACKTRACE)
+  list(APPEND linked_libraries ${Backtrace_LIBRARY})
+endif()
 
 include(CheckCXXSymbolExists)
 include(CheckCXXSourceCompiles)
@@ -271,7 +276,7 @@ if (NOT DEFINED MSVC)
   add_flang_library(FortranRuntime
     ${sources}
     LINK_LIBS
-    FortranDecimal
+    ${linked_libraries}
 
     INSTALL_WITH_TOOLCHAIN
   )
@@ -279,7 +284,7 @@ else()
   add_flang_library(FortranRuntime
     ${sources}
     LINK_LIBS
-    FortranDecimal
+    ${linked_libraries}
   )
   set(CMAKE_MSVC_RUNTIME_LIBRARY MultiThreaded)
   add_flang_library(FortranRuntime.static ${sources}

[brad0]

@tblah @dty2 @luporl @klausler

[tblah]

LGTM, thanks!

[Meinersbur]

If CMake knows to link to libexecinfo, doesn't mean that the flang driver does. This will influence how unittests are linked, but what ensures that an executable created by flang is linked correctly?

[tblah]

I'm definitely not an expert in this area but wouldn't this be a dependency of the runtime library so when the runtime library is loaded this would be too? Then flang just needs to know to link the runtime library

[Meinersbur]

I'm definitely not an expert in this area but wouldn't this be a dependency of the runtime library so when the runtime library is loaded this would be too? Then flang just needs to know to link the runtime library

If it is a static library, then no. There is no mechanism for transitive dependencies in ld.

[Meinersbur]

If CMake knows to link to libexecinfo, doesn't mean that the flang driver does. This will influence how unittests are linked, but what ensures that an executable created by flang is linked correctly?

#125998 does