[CMake] Fwd: Save stripped debugging information

Michael Hertling mhertling at online.de
Sat Oct 1 00:11:44 EDT 2011


On 09/30/2011 08:39 AM, Rolf Eike Beer wrote:
>> On 09/29/2011 06:15 AM, Yuri Timenkov wrote:
>>> When I was investigating similar problem, I found alternative approach
>>> at
>>> http://code.google.com/p/dynamorio/source/browse/trunk/CMakeLists.txt.
>>>
>>> The thing is to change linker rules, to something like this:
>>>     set(CMAKE_C_CREATE_SHARED_LIBRARY
>>>         # standard rule
>>>         "<CMAKE_C_COMPILER> <CMAKE_SHARED_LIBRARY_C_FLAGS>
>>> <LANGUAGE_COMPILE_FLAGS> <LINK_FLAGS>
>>> <CMAKE_SHARED_LIBRARY_CREATE_C_FLAGS>
>>> <CMAKE_SHARED_LIBRARY_SONAME_C_FLAG><TARGET_SONAME> -o <TARGET>
>>> <OBJECTS>
>>> <LINK_LIBRARIES>"
>>>         # now create a .debug copy
>>>         "${CMAKE_OBJCOPY} --only-keep-debug <TARGET> <TARGET>.debug"
>>>         # link original to point at .debug copy
>>>         # directory components are removed, so "../lib/" is fine
>>>         "${CMAKE_OBJCOPY} --add-gnu-debuglink=<TARGET>.debug <TARGET>"
>>>         # Strip all information from target binary.
>>>         "${CMAKE_STRIP} --strip-debug --discard-all --preserve-dates
>>> <TARGET>"
>>>     )
>>>
>>> I don't exactly remember benefits from this approach but it kind of
>>> works.
>>
>> The benefits are that one needs to define these rule variables once as
>> they're inherited by the subdirectories. The downside is that the rule
>> variables are used by Makefile generators only, whereas the target-
>> associated custom commands are a more generic approach.
>>
>>> And I agree that functionality like installing debug symbols in
>>> install()
>>> rules out of box would be quite handy.
>>
>> INSTALL() is essentially about copying files and directories, so it
>> doesn't depend on the toolchain; in particular, you can use INSTALL()
>> for projects which are configured with PROJECT(... NONE), i.e. without
>> any toolchain. By contrast, extracting debug symbols does highly depend
>> on the toolchain, e.g. the objcopy(1) utility isn't mentioned in POSIX,
>> and even with the GNU tools, you have multiple possibilities to connect
>> the stripped binary with the unstripped one, note --add-gnu-debuglink
>> vs. build IDs. Windows and MacOSX will further enrich this entire zoo
>> of utilities and command line switches, not to mention toolchains for
>> specific platforms. So, opening and parameterizing INSTALL() - w.r.t.
>> its interface and its implementation - in order to provide reasonable
>> support for the extraction of debug symbols during installation is a
>> major undertaking, IMO, besides the conceptional issue of toolchain-
>> dependence.
> 
> The idea was not to generate those during install, but to be able to let
> them being installed. For e.g. MSVC you don't have anything to do, the
> linker will already generate the PDB file already. So all you would have
> to do would be to copy the generated debug file to the proper place. This
> whish  comes from the fact that for multi-configuration generators you
> don't know which configuration is active so you don't know where to search
> the PDB file. And INSTALL() and ADD_CUSTOM_TARGET()/_COMMAND() don't
> understand generator expressions.

INSTALL() doesn't, but ADD_CUSTOM_TARGET/COMMAND() are right the two
commands which *do* understand generator expressions. As long as you
know the location of the debug files relative to the location of the
concerned target's binary, the $<TARGET_FILE_DIR:target> expressions
should do the trick. So, the worst case you might suffer is that you
must use a custom target/command to copy or move the debug files to
a suitable location in order to apply INSTALL(FILES ...) on them in
the end. IMO, that's bearable; does it not work for you? However,
adding generator expressions to the INSTALL() command might be
worth a thought.

> So my idea would be to generate the debug file during or after the link
> step and save the position to this file somewhere internally, so
> INSTALL(... DEBUG_SYMBOLS) would know which to take. Or to do just nothing
> if we do not support external debug symbols on this platform.

What do you mean with "save the position to this file somewhere
internally"? Saving by a user's action, i.e. declaring a file as a
debug file? If you know the file's name and location, you can simply
apply INSTALL(FILES ...) on it, perhaps with an intermediate step as
suggested above. Saving by action of CMake, i.e. without specifying
the debug file's name and/or location? For this to work, you would
need to teach CMake to recognize a debug file by itself, and that's
probably a comparably complicated undertaking as teaching CMake how
to generate debug files. E.g., with a typical *nix toolchain, CMake
has no chance to know in advance *if* a debug file is generated,
*where* it is written to and *what* is its name.

Regards,

Michael


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