[Lldb-commits] [PATCH] D13667: cmake: provide flag that enables 'log enable --stack' to provide useful file/line info on POSIX systems

[Todd Fiala via lldb-commits]

tfiala created this revision.
tfiala added reviewers: emaste, chaoren.
tfiala added subscribers: lldb-commits, labath.

This change addresses:
https://llvm.org/bugs/show_bug.cgi?id=25133

On Linux (and likely other GNU ld-based systems), the llvm backtrace utility used by 'log enable --stack' cannot walk through private symbols in liblldb.so.  This makes the --stack option useless just about everywhere but OS X.  This change provides a way to address that.

By default, nothing changes.  However, if the cmake -DLLDB_EXPORT_ALL_SYMBOLS=TRUE option is provided (also a CACHE variable, so can be set via UI), then on non-Windows systems, we'll drop exporting a named list of symbols, and tell the linker to export all symbols.  This allows the backtrace mechanism used by 'log enable --stack' to find file/line number info, and makes introspection of source code within lldb much more productive.

The change is a do-nothing operation on Windows.

On OS X cmake builds, the additional linker option is not needed (nor is it supported by the linker).

Google folks - feel free to adjust the Linux-side reviewers.  Just looking for representation.

Ed - I'd guess FreeBSD was in the same boat as Linux here.

http://reviews.llvm.org/D13667

Files:
  cmake/modules/AddLLDB.cmake
  cmake/modules/LLDBConfig.cmake
  source/API/CMakeLists.txt

Index: source/API/CMakeLists.txt
===================================================================
--- source/API/CMakeLists.txt
+++ source/API/CMakeLists.txt
@@ -82,7 +82,21 @@
   )
 
 if (NOT CMAKE_SYSTEM_NAME MATCHES "Windows")
-  add_llvm_symbol_exports(liblldb ${CMAKE_CURRENT_SOURCE_DIR}/liblldb.exports)
+  if (NOT LLDB_EXPORT_ALL_SYMBOLS)
+    # If we're not exporting all symbols, we'll want to explicitly set
+    # the exported symbols here.  This prevents 'log enable --stack ...'
+    # from working on some systems but limits the liblldb size.
+    MESSAGE("-- Symbols (liblldb): only exporting liblldb.exports symbols")
+    add_llvm_symbol_exports(liblldb ${CMAKE_CURRENT_SOURCE_DIR}/liblldb.exports)
+  else()
+    # Don't use an explicit export.  Instead, tell the linker to
+    # export all symbols.
+    MESSAGE("-- Symbols (liblldb): exporting all symbols")
+    # Darwin linker doesn't need this extra step.
+    if (NOT CMAKE_SYSTEM_NAME MATCHES "Darwin")
+      lldb_append_link_flags(liblldb "-Wl,--export-dynamic")
+    endif()
+  endif()
 endif()
 
 if ( CMAKE_SYSTEM_NAME MATCHES "Windows" )
Index: cmake/modules/LLDBConfig.cmake
===================================================================
--- cmake/modules/LLDBConfig.cmake
+++ cmake/modules/LLDBConfig.cmake
@@ -29,6 +29,15 @@
 set(LLDB_RELOCATABLE_PYTHON 0 CACHE BOOL
   "Causes LLDB to use the PYTHONHOME environment variable to locate Python.")
 
+if (NOT CMAKE_SYSTEM_NAME MATCHES "Windows")
+  set(LLDB_EXPORT_ALL_SYMBOLS 0 CACHE BOOL
+    "Causes lldb to export all symbols when building liblldb.")
+else()
+  # Windows doesn't support toggling this, so don't bother making it a
+  # cache variable.
+  set(LLDB_EXPORT_ALL_SYMBOLS 0)
+endif()
+
 if ((NOT MSVC) OR MSVC12)
   add_definitions( -DHAVE_ROUND )
 endif()
Index: cmake/modules/AddLLDB.cmake
===================================================================
--- cmake/modules/AddLLDB.cmake
+++ cmake/modules/AddLLDB.cmake
@@ -96,3 +96,19 @@
   add_llvm_executable(${name} ${ARGN})
   set_target_properties(${name} PROPERTIES FOLDER "lldb executables")
 endmacro(add_lldb_executable)
+
+# Support appending linker flags to an existing target.
+# This will preserve the existing linker flags on the
+# target, if there are any.
+function(lldb_append_link_flags target_name new_link_flags)
+  # Retrieve existing linker flags.
+  get_target_property(current_link_flags ${target_name} LINK_FLAGS)
+
+  # If we had any linker flags, include them first in the new linker flags.
+  if(current_link_flags)
+    set(new_link_flags "${current_link_flags} ${new_link_flags}")
+  endif()
+
+  # Now set them onto the target.
+  set_target_properties(${target_name} PROPERTIES LINK_FLAGS ${new_link_flags})
+endfunction()


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