[FFmpeg-cvslog] r20497 - trunk/configure

[David Conrad]

On Nov 16, 2009, at 7:01 AM, M?ns Rullg?rd wrote:

> David Conrad <lessen42 at gmail.com> writes:
> 
>> On Nov 15, 2009, at 2:43 PM, M?ns Rullg?rd wrote:
>> 
>>>>>>> Maybe it shouldn't be using the same variable for PIC being
>>>>>>> detected and the user specifically requesting it, but that won't
>>>>>>> fix this check, which either needs to not run for Darwin or to run
>>>>>>> after the flag is added.
>>>>>> 
>>>>>> Why is adding that flag conditional on PIC anyway?
>>>>> 
>>>>> IIRC it was supposed to do something allowing non-pic code in shared
>>>>> libs.  Now that doesn't make much sense if, as you say, PIC is always
>>>>> on with that compiler.
>>>>> 
>>>>> So which way is it?
>>>> 
>>>> No, it is supposed to allow avoiding some of the cost of PIC for binaries
>>>> by using PIC only where necessary (I think something like ebx must have
>>>> a specific value when calling system functions etc.).
>>> 
>>> Does not adding that flag break anything.  If not, screw OSX and
>>> remove the hack.  Nobody is forced to use OSX anyway, so they have
>>> only themselves to blame if it's slow.
>> 
>> It breaks gcc 4.2 and newer, which I see as unlikely to be fixed
>> ever given that the gcc darwin maintainers work on llvm instead
>> nowadays.
>> 
>> The only two hosts in the section that care about PIC are OpenBSD
>> and Darwin, OpenBSD unconditionally enables PIC, and the check is
>> broken on Darwin. The only other reason I can see it might not be
>> safe is check_cc, but that's already used before the arch section.
>> 
>> Not running the check on Darwin at all is another option, since PIC
>> is always enabled by default, but it's uglier.
> 
> Now I'm totally confused.  Can someone please complete the table below:

I counted -fPIC to include -DPIC in cppflags, all compilation failures due to this are noted and need only -DPIC to work.
-mdynamic-no-pic overrides -fPIC and warns about it.
Also, MANGLE means that x86-32 is never fully PIC.

x86-32, gcc < 4.2
       static  shared  -fPIC   -mdynamic-no-pic  |  works
--------------------------------------------------+--------
1       x                                         |  N (needs -DPIC for swscale)
2       x               x                         |  Y (PIC)
3       x                       x                 |  Y (non-PIC)
4       x               x       x                 |  Y (non-PIC)
5               x                                 |  N (needs -DPIC for swscale)
6               x       x                         |  Y (PIC)
7               x               x                 |  Y (non-PIC)
8               x       x       x                 |  Y (non-PIC)

x86-32, gcc >= 4.2 (compilation failures due to gcc bugs with inline asm)
       static  shared  -fPIC   -mdynamic-no-pic  |  works
--------------------------------------------------+--------
1       x                                         |  N
2       x               x                         |  N
3       x                       x                 |  Y
4       x               x       x                 |  Y
5               x                                 |  N
6               x       x                         |  N
7               x               x                 |  Y
8               x       x       x                 |  Y

x86-64 (flags ignored, always PIC)
       static  shared  -fPIC   -mdynamic-no-pic  |  works
--------------------------------------------------+--------
1       x                                         |  N (needs -DPIC)
2       x               x                         |  Y
3       x                       x                 |  Y
4       x               x       x                 |  Y
5               x                                 |  N (needs -DPIC)
6               x       x                         |  Y
7               x               x                 |  Y
8               x       x       x                 |  Y

PPC
       static  shared  -fPIC   -mdynamic-no-pic  |  works
--------------------------------------------------+--------
1       x                                         |  Y
2       x               x                         |  Y
3       x                       x                 |  Y
4       x               x       x                 |  Y
5               x                                 |  Y
6               x       x                         |  Y
7               x               x                 |  *
8               x       x       x                 |  Y
* -mdynamic-no-pic + shared appears to work for me, but it is heavily recommended against doing. I can't explain why unfortunately.