SDK size reduction about drishti HOT 12 CLOSED

See: https://wiki.wxwidgets.org/Reducing_Executable_Size

"Pass -ffunction-sections -fdata-sections to the compiler while building and -Wl,--gc-sections to the linker"

Create a toolchain file that compiles the library and all Hunter dependencies with:
-ffunction-sections -fdata-sections

And be sure to link with

  CHECK_C_COMPILER_FLAG("-Wl,-dead_strip" FLAG_dead_strip)
  IF(NOT FLAG_dead_strip)
    SET(CMAKE_SHARED_LINKER_FLAGS "-Wl,--gc-sections")
  ELSE()
    SET(CMAKE_SHARED_LINKER_FLAGS "-Wl,-dead_strip")
  ENDIF()

http://stackoverflow.com/a/18115676

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Also -flto might help
http://stackoverflow.com/a/31355020
GCC: https://gcc.gnu.org/wiki/LinkTimeOptimization
Clang: https://llvm.org/docs/LinkTimeOptimization.html

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Another options:

• Try -O2 instead of -O3
• Try -Os (MinSizeRel)
• Single Compilation Unit. This is something that is not implemented in CMake so just for the record.

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DELETE

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DELETE

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http://stackoverflow.com/a/18949281

    XCODE_ATTRIBUTE_GENERATE_MASTER_OBJECT_FILE "YES" # "Perform Single-Object Prelink"

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I've added a lightweight c interface (remove rtti, etc) and strip everything except the explicitly defined symbols table (details below) and can get the sdk down to 2.2 MB from the previous 8.0 MB. This is also using a new xcode-sections toolchain for all hunter dependencies.

6.9M _install/xcode-sections/lib/libdrishti.0.7.1.dylib
4.0K _install/xcode-sections/lib/libdrishti.0.dylib
4.0K _install/xcode-sections/lib/libdrishti.dylib
2.2M _install/xcode-sections/lib/libdrishti_c.dylib
792K _install/xcode-sections/lib/libdrishti_c.dylib.gz

function(drishti_hide_and_strip drishti_library)
  set_target_properties(${drishti_library}
    PROPERTIES
    CXX_VISIBILITY_PRESET hidden  ### HIDE
    VISIBILITY_INLINES_HIDDEN "ON"
    XCODE_ATTRIBUTE_GCC_INLINES_ARE_PRIVATE_EXTERN "YES"
    XCODE_ATTRIBUTE_GCC_SYMBOLS_PRIVATE_EXTERN "YES"
    XCODE_ATTRIBUTE_COPY_PHASE_STRIP "YES"
    XCODE_ATTRIBUTE_STRIP_INSTALLED_PRODUCT "YES"
    XCODE_ATTRIBUTE_STRIP_STYLE "non-global"
    XCODE_ATTRIBUTE_STRIPFLAGS "-x -u -r"
    XCODE_ATTRIBUTE_DEAD_CODE_STRIPPING "YES"
    XCODE_ATTRIBUTE_DEPLOYMENT_POSTPROCESSING "YES"
    XCODE_ATTRIBUTE_GENERATE_MASTER_OBJECT_FILE "YES" # "Perform Single-Object Prelink"
    PUBLIC_HEADER "${DRISHTI_DRISHTI_HDRS_PUBLIC}"
    )
endfunction(drishti_hide_and_strip)

  drishti_hide_and_strip(drishti_c)

  set_target_properties(drishti_c
    PROPERTIES
    XCODE_ATTRIBUTE_EXPORTED_SYMBOLS_FILE "${CMAKE_CURRENT_LIST_DIR}/drishti/drishti_symbols.txt"
    )

drishti_symbols.txt:

_drishti_create_from_file
_drishti_create_from_stream
_drishti_destroy
_drishti_segment

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Switching to MinSizeRel and dropping the unnecessary text archive support on OS X saves a bit more:

5.9M libdrishti.0.7.1.dylib
4.0K libdrishti.0.dylib
4.0K libdrishti.dylib
1.9M libdrishti_c.dylib
716K libdrishti_c.dylib.gz

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This stripped _c.dylib.gz size is suitable. The issue can be closed once the post build install() libraries are actually tested. See #75

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See #138

This is really an ongoing effort. The eye sdk size is significantly reduced using the above C interface, and initial comparisons were done in #138, so I'm removing this from the current milestone in favor of more focused follow up efforts.

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Some Apple notes on size reduction "How to best..."
https://developer.apple.com/library/content/technotes/tn2185/_index.html

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This was on the right path but was missing: -flto -Os and related per platform linker flags (as needed) to get the full savings. Satisfied with current approach after boost -> cereal updates + extern "C" api + strip + -flto -Os -fdata-sections -ffunction-sections

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