[llvm-commits] [patch][gold plugin] Don't preserve all symbols in a .so

[Rafael Espindola]

With the attached patch the plugin will no longer preserve all symbols
in a .so and instead will trust gold to know what is needed. The
result is that it is now able to drop unnecessary symbol from shared
libraries. An example adapted from
http://llvm.org/releases/2.6/docs/LinkTimeOptimization.html:

$ clang -c a.c -emit-llvm -fdata-sections -ffunction-sections -fPIC
$ clang -c main.c -fdata-sections -ffunction-sections -fPIC
$ ld --no-add-needed --eh-frame-hdr --build-id -m elf_x86_64
--hash-style=gnu -shared -o foo.so
/usr/lib/gcc/x86_64-redhat-linux/4.4.4/../../../../lib64/crti.o
/usr/lib/gcc/x86_64-redhat-linux/4.4.4/crtbeginS.o
-L/usr/lib/gcc/x86_64-redhat-linux/4.4.4
-L/usr/lib/gcc/x86_64-redhat-linux/4.4.4
-L/usr/lib/gcc/x86_64-redhat-linux/4.4.4/../../../../lib64
-L/lib/../lib64 -L/usr/lib/../lib64
-L/usr/lib/gcc/x86_64-redhat-linux/4.4.4/../../.. main.o a.o -lgcc
--as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s
--no-as-needed /usr/lib/gcc/x86_64-redhat-linux/4.4.4/crtendS.o
/usr/lib/gcc/x86_64-redhat-linux/4.4.4/../../../../lib64/crtn.o
-plugin=/home/espindola/llvm/build/Debug/lib/LLVMgold.so
--gc-sections -plugin-opt=generate-api-file
$ cat apifile.txt
foo1
foo5
$ objdump  -d foo.so | grep foo4

Gold itself is still not as aggressive as it could be, but that is
another patch :-)

And yes, I do have to implement support for gold plugin's in clang!

Cheers,
-- 
Rafael Ávila de Espíndola
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