[phobos] 32 and 64 bit libraries on Linux

[Walter Bright]

Thanks, I think I'll give this schema a try and see how it works. -Walter

Jonathan M Davis wrote:
> On Tuesday, January 04, 2011 15:18:16 Walter Bright wrote:
>   
>> The command and the barf:
>>
>> gcc foo.o -o foo -m32 -Xlinker -L/home/walter/cbx/mars1/phobos -lphobos
>> -lpthread -lm
>> /usr/bin/ld: skipping incompatible
>> /home/walter/cbx/mars1/phobos/libphobos.a when searching for -lphobos
>> /usr/bin/ld: cannot find -lphobos
>> collect2: ld returned 1 exit status
>> --- errorlevel 1
>>
>>
>> So, what to do?
>>
>> 1. what to name the libraries?
>> 2. where to put the libraries?
>> 3. how should dmd invoke gcc to do the linking?
>> 4. what goes in dmd.conf?
>>
>> 1,2,3 for -m32, -m64, and the default?
>>     
>
> I would think that the issue is that the correct libphobos.a isn't on the 
> linker's path. It looks like /home/walter/cbx/mars1/phobos/libphobos.a is the 
> wrong version. I believe that for -lphobos to work, the library must be named 
> exactly libphobos.a, be compiled for the correct architecture, and be in the 
> linker's bath. So, if you don't have a libphobos.a of the correct architecture 
> on the linker's path, then the linking will fail.
>
> If both the 32-bit and 64-bit versions are included in the linker's path, then I 
> would expect the linker to select the correct one. So, if you had directories 
> such as lib32 and lib64 in the distributed zip file, both of them have a 
> libphobos.a of the corresponding architecture, and dmd.conf includes -L 
> arguments for both directories, then the linker should find them and use the 
> correct one. Then, if the user or distribution maintainer wishes to put them 
> elsewhere (such as /usr/lib or /usr/lib64), then they either just move them to 
> the desired location and alter dmd.conf so that the -L arguments point to 
> wherever they put the libraries (or probably just remove the -L arguments if 
> they put the libraries somewhere where ld already looks on their system).
>
> So, I would think that the correct things to do would be
>
> 1. Name them both libphobos.a.
>
> 2. Put the libraries in separate directories - probably named lib32 and lib64 - 
> somewhere in the zip file (you should probably just replace the current lib 
> directories with a lib32 and lib64 directory).
>
> 4. Assuming that you replaced linux/lib with linux/lib32 and linux/lib64, then 
> you remove -L-L%@P%/../lib from the current dmd.conf and add -L-L%@P%/../lib32 
> and -L-L%@P%/../lib64. If you're compiling with -m32, the linker will use the 
> 32-bit version, and if you're compiling with -m64, it'll use the 64-bit version. 
> Anyone who wants to put the libraries elsewhere can just edit their dmd.conf 
> accordingly.
>
> 3. I'm not all that well-versed in gcc, so maybe there's some nuance I'm 
> missing. But what you're doing there looks right as long as the -L flags point to 
> the correct directories. Use -m32 for 32-bit builds and -m64 for 64-bit builds.
>
> Now, I'm not quite sure how you'd deal with the default value for -m. Normally, 
> I'd expect you to have a 32-bit version of dmd if you're on a 32-bit system and 
> a 64-bit version of dmd if you're on a 64-bit system. Then the 32-bit version 
> defaults to -m32, and the 64-bit version defaults to -m64. But as I understand 
> it, you're not currently planning to do a 64-bit version of dmd.... gcc will be 
> 32-bit or 64-bit and therefore will default to the correct architecture if you 
> don't give it a value for -m, but dmd is still going to need to know the 
> architecture for the compilation phase, so you can't just skip the -m when 
> linking and expect that to work. It sounds like dmd is going to need a way to 
> know what architecture it's currently compiling on, or it's going to have to 
> default to 32-bit (which would be less than ideal). Once it's determined the 
> correct architecture, it can use that for the compilation phase, and it will 
> know whether to use -m32 or -m64 in the linking phase.
>
> I am by no means an expert on how linking and libraries work on Linux, but I 
> have been using primarily 64-bit multilib Linux systems for a while, so I think 
> that I have a fair grasp of the situation, and I _think_ that what I've said is 
> correct, but I could be missing something vital. If this information isn't 
> enough, then hopefully someone else more knowledgeable can chime in.
>
> - Jonathna M Davis
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