[FFmpeg-devel] fft_mmx.asm yasm 64bit build broken

D lessen42
Sat Aug 16 18:20:15 CEST 2008

On Aug 16, 2008, at 11:59 AM, Robert Swain wrote:

> 2008/8/16 M?ns Rullg?rd <mans at mansr.com>:
>> vmrsss <vmrsss at gmail.com> writes:
>>> On 16 Aug 2008, at 15:49, M?ns Rullg?rd wrote:
>>>> Ask Apple if they can fix the system.  We don't know.
>>> What do you mean? Doesn't look like a Apple problem at all...
>>>> error: macho: sorry, cannot apply 32 bit absolute relocations in 64
>>>> bit mode, consider "[_symbol wrt rip]" for mem access, "qword" and
>>>> "dq _foo" for pointers.
>> This is an Apple problem.  Since the same code works on the same
>> hardware under Linux, it follows that it must be an Apple problem if
>> it doesn't work in MacOS.  In fact, code like this used to work just
>> fine with older versions of the Apple linker.  Sorry, but you're
>> barking up the wrong tree.
> I don't think this is that linker issue about text relocations. The
> errors are being spewed by yasm, are they not?

Indeed, from yasm's macho-objfmt.c:

   2.2) data referencing in 64 bit mode
        While ELF allows 32 bit absolute relocations in 64 bit mode,  
        does not. Therefore code like
         lea rbx,[_foo]  ;48 8d 1c 25 00 00 00 00
         mov rcx,[_bar]  ;48 8b 0c 25 00 00 00 00
        with a 32 bit address field cannot be relocated into an address
        >= 0x100000000 (OSX actually uses that).

        Actually, the only register where a 64 bit displacement is  
allowed in
        x86-64, is rax as in the example 1).

        A plausible workaround is either classic PIC (like in C),  
which is in turn
        not implemented in this object format. The recommended was is  
PC relative
        code (called RIP-relative in x86-64). So instead of the lines  
above, just write:
         lea rbx,[_foo wrt rip]
         mov rcx,[_bar wrt rip]

x264 uses -DPIC unconditionally for asm code in the x86_64/macho case.
Additionally, ffmpeg was using macho rather than macho64 in this case.

The attached patch the ffmpeg build on x86_64/darwin.

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