[libcxxabi] r228408 - unwind: use -fno-rtti -fno-exceptions -funwind-tables
Anton Korobeynikov
anton at korobeynikov.info
Fri Feb 13 10:48:14 PST 2015
Since the stuff is heavily broken at this moment, shall we revert the
detection stuff for a moment?
On Fri, Feb 13, 2015 at 7:36 PM, Saleem Abdulrasool
<compnerd at compnerd.org> wrote:
> On Thu, Feb 12, 2015 at 1:13 PM, Sergey Dmitrouk
> <sdmitrouk at accesssoftek.com> wrote:
>>
>> How about the attached patch? Seems to work for me (it's trivial, but
>> syntax is weird, so I wasn't sure).
>
>
> It would prevent building unwind as a DSO without libc++abi linked in, so,
> this isn't the way to handle this. I think you need to tweak the detection
> of the -funwind-tables option.
>
>>
>>
>> --
>> Sergey
>>
>> On Thu, Feb 12, 2015 at 07:36:14AM -0800, Sergey Dmitrouk wrote:
>> > On Thu, Feb 12, 2015 at 07:13:09AM -0800, Saleem Abdulrasool wrote:
>> > > I've been successful with clang as well.
>> > > Reproduction steps would help in identifying what is happening.
>> >
>> > Looks like I found the culprit, it's CMake. I'm cross compiling
>> > libcxxabi for ARM on x86_64 host, compiler targets ARM only (so ARM is
>> > also the default target). cmake/config-ix.cmake contains (also note
>> > "_c_"
>> > instead of "_cxx_", but it doesn't affect results):
>> >
>> > check_c_compiler_flag(-funwind-tables LIBCXXABI_HAS_FUNWIND_TABLES)
>> >
>> > This test fails on linking stage:
>> >
>> >
>> > CMakeFiles/cmTryCompileExec3829915952.dir/src.cxx.o:(.ARM.exidx+0x0):
>> > undefined reference to `__aeabi_unwind_cpp_pr0'
>> >
>> > because successful linking requires symbol defined in libunwind (and
>> > that's
>> > what is being built). Now here:
>> >
>> > append_if(LIBUNWIND_COMPILE_FLAGS LIBCXXABI_HAS_NO_EXCEPTIONS_FLAG
>> > -fno-exceptions)
>> > append_if(LIBUNWIND_COMPILE_FLAGS LIBCXXABI_HAS_NO_RTTI_FLAG
>> > -fno-rtti)
>> > append_if(LIBUNWIND_COMPILE_FLAGS LIBCXXABI_HAS_FUNWIND_TABLES
>> > -funwind-tables)
>> >
>> > `-fno-exceptions` is added, but not `-funwind-tables`. As a result
>> > libunwind sees "can't unwind" marker in exidx records and gives up.
>> >
>> > I found this bug report, which seems to be related:
>> > http://www.cmake.org/Bug/view.php?id=15264
>> >
>> > Not adding `-fno-exceptions` flag if `-funwind-tables` isn't available
>> > seems
>> > to be reasonable by itself, but will also work around this issue with
>> > CMake.
>> >
>> > --
>> > Sergey
>
>
>
>
> --
> Saleem Abdulrasool
> compnerd (at) compnerd (dot) org
>
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--
With best regards, Anton Korobeynikov
Faculty of Mathematics and Mechanics, Saint Petersburg State University
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