Default to linking lldb-server statically for Android.

[tberghammer]

cmake/platforms/Android.cmake

98–102 ↗

(On Diff #28835)

Who will specify the "-pie" flag for API 21+? Without it lldb-server won't work in those API levels.

[chaoren]

-pie is not compatible with -static. lldb-server can work on any API if
linked statically.

[tberghammer]

Thanks for the explanation.

[tberghammer]

What is the implication of this change in terms of the size of lldb-server?

You are linking statically against the system libraries (such as libc, libm, libdl) what might not be a portable solution if they are depending on features only present in some device / kernel.

[labath]

In D10858#198371, @tberghammer wrote:

You are linking statically against the system libraries (such as libc, libm, libdl) what might not be a portable solution if they are depending on features only present in some device / kernel.

The platforms should be backward compatible. A binary which works on an older device (statically linked or not) should work on newer devices as well, so I don't anticipate problems of this sort. However, libc is pretty big, so the size question is valid imho.

[chaoren]

The resulting binary size is almost identical to the one that's dynamically
linked.

[chaoren]

• Add comment for rational.

lldb/trunk/cmake/LLDBDependencies.cmake

 
 if (NOT LLDB_DISABLE_PYTHON AND NOT LLVM_BUILD_STATIC)
   list(APPEND LLDB_SYSTEM_LIBS ${PYTHON_LIBRARIES})
 endif()
 
 list(APPEND LLDB_SYSTEM_LIBS ${system_libs})
 
 if (LLVM_BUILD_STATIC)
-  list(APPEND LLDB_SYSTEM_LIBS python2.7 z util termcap gpm ssl crypto bsd)
+  if (NOT LLDB_DISABLE_PYTHON)
+    list(APPEND LLDB_SYSTEM_LIBS python2.7 util)
+  endif()
+  if (NOT LLDB_DISABLE_CURSES)
+    list(APPEND LLDB_SYSTEM_LIBS gpm)
+  endif()
 endif()
 
 set( LLVM_LINK_COMPONENTS
   ${LLVM_TARGETS_TO_BUILD}
   interpreter
   asmparser
   bitreader
   bitwriter

lldb/trunk/cmake/platforms/Android.cmake

 include( CMakeForceCompiler )
 
 # flags and definitions
 remove_definitions( -DANDROID -D__ANDROID__ )
 add_definitions( -DANDROID -D__ANDROID_NDK__ -DLLDB_DISABLE_LIBEDIT )
 set( ANDROID True )
 set( __ANDROID_NDK__ True )
 
+# linking lldb-server statically for Android avoids the need to ship two
+# binaries (pie for API 21+ and non-pie for API 14-). It's possible to use
+# a non-pie shim on API 14-, but that requires lldb-server to dynamically export
+# its symbols, which significantly increases the binary size. Static linking, on
+# the other hand, has little to no effect on the binary size.
+if (NOT DEFINED LLVM_BUILD_STATIC)
+ set( LLVM_BUILD_STATIC True )
+endif()
+
 set( ANDROID_ABI "${ANDROID_ABI}" CACHE INTERNAL "Android Abi" FORCE )
 if( ANDROID_ABI STREQUAL "x86" )
  set( CMAKE_SYSTEM_PROCESSOR "i686" )
  set( ANDROID_TOOLCHAIN_NAME "i686-linux-android" )
 elseif( ANDROID_ABI STREQUAL "x86_64" )
  set( CMAKE_SYSTEM_PROCESSOR "x86_64" )
  set( ANDROID_TOOLCHAIN_NAME "x86_64-linux-android" )
 elseif( ANDROID_ABI STREQUAL "armeabi" )

 if( X86 )
  set( ANDROID_CXX_FLAGS "${ANDROID_CXX_FLAGS} -funswitch-loops -finline-limit=300" )
 elseif( ANDROID_ABI STREQUAL "armeabi" )
  # 64 bit atomic operations used in c++ libraries require armv7-a instructions
  # armv5te and armv6 were tried but do not work.
  set( ANDROID_CXX_FLAGS "${ANDROID_CXX_FLAGS} -march=armv7-a" )
 endif()
 
-# PIE is required for API 21+ so we enable it
-# unfortunately, it is not supported before API 14 so we need to do something else there
-# see http://llvm.org/pr23457
-set( ANDROID_CXX_FLAGS "${ANDROID_CXX_FLAGS} -pie -fPIE" )
-
 # linker flags
 set( ANDROID_CXX_FLAGS    "${ANDROID_CXX_FLAGS} -fdata-sections -ffunction-sections" )
 set( ANDROID_LINKER_FLAGS "${ANDROID_LINKER_FLAGS} -Wl,--gc-sections" )
 
 # cache flags
 set( CMAKE_CXX_FLAGS           ""                        CACHE STRING "c++ flags" )
 set( CMAKE_C_FLAGS             ""                        CACHE STRING "c flags" )
 set( CMAKE_EXE_LINKER_FLAGS    "-Wl,-z,nocopyreloc"      CACHE STRING "executable linker flags" )