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digitalmars.D.learn - OT: Linux shared lib question

reply Bill Baxter <dnewsgroup billbaxter.com> writes:
Not really a D question, but I'm hoping someone out there knows the 
answer (it is for the purpose of getting my D Multiarray library working 
better on Linux, though.)

I want to create a shared .so from a .a library.

I found on a web page somewhere that a .so can be created from some .o 
files using something like the following:

   gcc -shared -Wl,-soname,lib${name}.so.1 -o lib${name}.so.1.1 \
       a.o b.o c.o

So I figured if it can do that then surely this would work:

   gcc -shared -Wl,-soname,lib${name}.so.1 -o lib${name}.so.1.1 \
       libmylibrary.a

where libmylibrary.a is a lib containing a.o, b.o, and c.o.  After all a 
.a archive is basically just a concatenation of .o files in a convenient 
package.

However, though the command runs without reporting an error, the 
resulting .so does not contain the contents of libmylibrary.a.

SO what I'm doing now in my "make .so from .a" script is basically this:
     mkdir tmp
     cd tmp
     ar x path/to/libmylibrary.a
     gcc -shared -Wl,-soname,libfoo.so.1 -o libfoo.so.1.1  *.o
     rm *.o
     cd ..
     rmdir tmp


Extract the .o's from the .a, make the shared lib using that, then clean 
up.

Is that really the best way to do this?  With MinGW you can directly 
create a dll from a .a, so I was a bit surprised to find out that the 
same gcc flags do not work on Linux to create a .so.  Is this a case 
where the Windows version of a GNU tool is actually easier to use than 
the Linux version?

--bb
May 12 2008
parent reply e-t172 <e-t172 akegroup.org> writes:
Bill Baxter a écrit :
 So I figured if it can do that then surely this would work:
 
   gcc -shared -Wl,-soname,lib${name}.so.1 -o lib${name}.so.1.1 \
       libmylibrary.a
 
 where libmylibrary.a is a lib containing a.o, b.o, and c.o.  After all a 
 .a archive is basically just a concatenation of .o files in a convenient 
 package.
 
 However, though the command runs without reporting an error, the 
 resulting .so does not contain the contents of libmylibrary.a.

man ld: "--whole-archive For each archive mentioned on the command line after the --whole-archive option, include every object file in the archive in the link, rather than searching the archive for the required object files. This is normally used to turn an archive file into a shared library, forcing every object to be included in the resulting shared library. This option may be used more than once. Two notes when using this option from gcc: First, gcc doesn’t know about this option, so you have to use -Wl,-whole-archive. Second, don’t forget to use -Wl,-no-whole-archive after your list of archives, because gcc will add its own list of archives to your link and you may not want this flag to affect those as well."
May 13 2008
parent Bill Baxter <dnewsgroup billbaxter.com> writes:
e-t172 wrote:
 Bill Baxter a écrit :
 So I figured if it can do that then surely this would work:

   gcc -shared -Wl,-soname,lib${name}.so.1 -o lib${name}.so.1.1 \
       libmylibrary.a

 where libmylibrary.a is a lib containing a.o, b.o, and c.o.  After all 
 a .a archive is basically just a concatenation of .o files in a 
 convenient package.

 However, though the command runs without reporting an error, the 
 resulting .so does not contain the contents of libmylibrary.a.

man ld: "--whole-archive For each archive mentioned on the command line after the --whole-archive option, include every object file in the archive in the link, rather than searching the archive for the required object files. This is normally used to turn an archive file into a shared library, forcing every object to be included in the resulting shared library. This option may be used more than once. Two notes when using this option from gcc: First, gcc doesn’t know about this option, so you have to use -Wl,-whole-archive. Second, don’t forget to use -Wl,-no-whole-archive after your list of archives, because gcc will add its own list of archives to your link and you may not want this flag to affect those as well."

Ah ok, Thanks! I had a magic invocation I used on Windows that looked like this: -gcc -mno-cygwin -shared -o umfpack.dll -Wl,--out-implib=umfpackdll.lib -Wl,--export-all-symbols -Wl,--allow-multiple-definition -Wl,--enable-auto-import -Wl,--whole-archive Lib/libumfpack.a ../AMD/Lib/libamd.a -Wl,--no-whole-archive ../lib/liblapack.a ../lib/libf77blas.a ../lib/libatlas.a -lg2c But Linux gcc barfed on the --export-all-symbols. So I assumed incorrectly that the rest of the bits there must be bogus for Linux too. Thanks for the explanation. Good tutorial explanations of this stuff from an ordinary developer perspective seem to be hard to find. --bb
May 13 2008