Dynamically loaded PIC shared library has runtime unresolved symbols from NPIC dependency

Question

Here's my situation

I have a shared library (PIC) foo.so. It uses symbols from bar.a. bar.a is NPIC. So can't be added to link line of foo.so.

foo.so is dynamically loaded from main.C It loads fine but at run time when a symbol from bar.a is used, it exits with unresolved symbol.

2 solutions I have been suggested 1. Compile bar.a PIC and add it to the link line of foo.so 2. Use " -Wl,--whole-archive bar.a -rdynamic" on main.C link line

1 is not possible because bar.a is a third party library. 2 is not possible because we dont' want our symbols to be exported.

Are there any other idioms/solutions to get around this problem?

Am I right in that: you do not really link against foo.so, you just use it via dlopen, etc? — Konstantin Vladimirov, Aug 22 '16 at 17:28

score 0 · Answer 1 · edited May 23 '17 at 12:15

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"1 is not possible because bar.a is a third party".

That does not sound right to me. Any static library can be linked against. That is the idiom to use. Also take a look at this answer and this one

edited May 23 '17 at 12:15

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answered Aug 22 '16 at 17:16

xtofl

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Disagree. Imagine, you just have no access to sources to supply -fPIC option. – Konstantin Vladimirov Aug 22 '16 at 17:20
What Konstantin said. We don't have access to the source to build with -fPIC – PdxEngineer Aug 22 '16 at 17:26
@KonstantinVladimirov: PIC or no PIC is really a _loader_ problem, not a linker one. Or am I mistaken? – xtofl Aug 22 '16 at 17:28
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@xtofl there are still some possibilities (like explicit dlopen on foo.so) where it might be loaded really messed up. Mixing PIC and non-PIC is dangerous. – Konstantin Vladimirov Aug 22 '16 at 17:32

score 0 · Answer 2 · answered Aug 22 '16 at 17:37

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There is one old good idiom. I call it "libgcc.so idiom" because it is often used in normal libgcc build, when you are creating libgcc_s.so from libgcc.a

Take you bar.a and make bar.so with this line:

gcc -shared -o bar.so -Wl,--whole-archive bar.a -Wl,--no-whole-archive

You may need to supply also something like -nostdlib or so.

And now go and link foo.so with this new bar.so

Now all dependencies will be resolved by dynamic linker when foo.so is loaded.

answered Aug 22 '16 at 17:37

Konstantin Vladimirov

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Is -fPIC option needed while making bar.so? – PdxEngineer Aug 22 '16 at 17:46
AFAIC no. This option is only about code generation, but no code generation happens here – Konstantin Vladimirov Aug 23 '16 at 07:11

Dynamically loaded PIC shared library has runtime unresolved symbols from NPIC dependency

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