[FFmpeg-cvslog] r10187 - trunk/configure

[David Conrad]

On Aug 25, 2007, at 7:03 PM, M?ns Rullg?rd wrote:

> David Conrad <umovimus at gmail.com> writes:
>
>> On Aug 25, 2007, at 4:40 PM, Guillaume POIRIER wrote:
>>
>>> Hi,
>>>
>>> On 8/22/07, mru <subversion at mplayerhq.hu> wrote:
>>>> Author: mru
>>>> Date: Wed Aug 22 22:42:25 2007
>>>> New Revision: 10187
>>>>
>>>> Log:
>>>> fix endian check when cross-compiling
>>>
>>> This commit broke PPC target. You reproduce the bug quite simply by
>>> trying to play a H264 file with ffplay:
>>>
>>> ./ffplay_g ~/Movies/CityLights.avi
>>> [h264 @ 0x361788]top block unavailable for requested intra mode at
>>> 13 0
>
> [...]
>
>>> I have no idea what the correct fix for this is though :(
>>
>> It seems that the strings on Mac OS X doesn't find the BIGE in the
>> object file unless you use - as in the attached patch. Don't know if
>> it's correct to do on other platforms though.
>>
>>
>> diff --git a/configure b/configure
>> index a9a4fd7..a6906b1 100755
>> --- a/configure
>> +++ b/configure
>> @@ -1522,7 +1522,7 @@ EOF
>>  check_cc <<EOF || die "endian test failed"
>>  unsigned int endian = 'B' << 24 | 'I' << 16 | 'G' << 8 | 'E';
>>  EOF
>> -strings $TMPO | grep -q BIGE && enable bigendian
>> +strings - $TMPO | grep -q BIGE && enable bigendian
>>
>>  # ---
>>  # check availability of some header files
>
> That should be safe on any conforming platform.  I don't understand
> how this could make a difference though.  Can someone please explain
> what's going on?  What is special about strings on macos?

It seems that strings on Mac OS X doesn't recognize a string if it's  
the minimum string length (default of 4) and ends on a section end  
without a newline/null within the section. The test case is being  
compiled so that the data section is 4 bytes long, containing only  
the BIGE string. Since - ignores Mach-O sections, the string is found  
without a problem because the next byte outside the section is 0.  
Using a longer string also works, as does ensuring that there's a  
null byte in the data section.