[CMake] Fwd: Save stripped debugging information

Yuri Timenkov yuri at timenkov.ru
Sat Oct 1 04:07:19 EDT 2011


that's the problem: you don't know neither file name nor it's location,
especially in multi-configuration generators.
It's also bad idea to mix build and install steps. Install command doesn't
understand generators expressions.

If it were possible to emulate vs behavior for gcc things would be much
easier in some cases. However extracting debug info from binaries is
performed by packager (at least rpmbuild does this)

On Oct 1, 2011 8:09 AM, "Michael Hertling" <mhertling at online.de> wrote:
> 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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