resolving weak symbols.

resolving weak symbols.

[Tom Kacvinsky]

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HI,

Support I have a static archive libfoo.a that has a weak sym, call it quux.

And the link line I have is

gcc -o foo -L. -lfoo -Wl,--as-needed -lbar -lbaz

Where libbar.so and libbaz.so also have the weak symbol quux.

Then the executable foo has a dynamic dependency on both libbar.so _and_
libbaz.so.

Is this expected behavior?  Is there a way of forcing exactly one of
libfoo.so and libbaz.so to be used?

Thanks,

Tom

Re: resolving weak symbols.

[Alan Modra]

On Thu, Mar 28, 2024 at 06:58:36PM -0400, Tom Kacvinsky wrote:
> HI,
> 
> Support I have a static archive libfoo.a that has a weak sym, call it quux.
> 
> And the link line I have is
> 
> gcc -o foo -L. -lfoo -Wl,--as-needed -lbar -lbaz
> 
> Where libbar.so and libbaz.so also have the weak symbol quux.
> 
> Then the executable foo has a dynamic dependency on both libbar.so _and_
> libbaz.so.
> 
> Is this expected behavior?  Is there a way of forcing exactly one of
> libfoo.so and libbaz.so to be used?

Works fine for me on x86_64-linux.  You'll notice that I'm not using
gcc to link.  Perhaps something in the way your gcc is invoking the
linker is getting in the way.  It pays to check what gcc is doing by
adding -v to the gcc command line.  It is also worthwhile checking
what you think is going on, by creating a little testcase like the
following.

cat > quux.s <<EOF
 .weak quux
 .data
quux: .byte 0
EOF
cat > quuxref.s <<EOF
 .data
 .dc.a quux
EOF
as -o quux.o quux.s
as -o quuxref.o quuxref.s
ld -shared -o lib1.so quux.o
ld -shared -o lib2.so quux.o
ld -o quux quuxref.o --as-needed lib1.so lib2.so
readelf -aW quux | grep NEEDED
ld: warning: type and size of dynamic symbol `quux' are not defined
ld: warning: cannot find entry symbol _start; defaulting to 0000000000401000
 0x0000000000000001 (NEEDED)             Shared library: [lib1.so]

-- 
Alan Modra
Australia Development Lab, IBM

Re: resolving weak symbols.

[Nick Clifton]

Hi Tom,

> Suppose I have a static archive libfoo.a that has a weak sym, call it quux.
> 
> And the link line I have is
> 
> gcc -o foo -L. -lfoo -Wl,--as-needed -lbar -lbaz
> 
> Where libbar.so and libbaz.so also have the weak symbol quux.
> 
> Then the executable foo has a dynamic dependency on both libbar.so _and_ libbaz.so.
> 
> Is this expected behavior?  Is there a way of forcing exactly one of libfoo.so and libbaz.so to be used?

Probably not, but I think that we will need a full example (source
files + command lines) to be sure.  It would also help if you could
file this as a potential bug report in the bugzilla system so that
we can track it:  https://sourceware.org/bugzilla/

Cheers
   Nick