I have a problem linking some shared library with g++. It gives me a warning like:
hidden symbol XXX in YYY is referenced by DSO /usr/lib/...
What is a DSO?
A DSO is a Dynamic Shared Object, or less formally a shared library.
What is a hidden symbol?
A hidden symbol is a symbol (i.e. name of function or data object) that has been compiled with hidden linkage, e.g. as per the (GCC specific) declaration:
int x __attribute__ ((visibility ("hidden")));
x is defined in one DSO then dynamic linkage cannot reference it from a
different DSO. The linker can see
x (it is not
static), but it is not
available for dynamic linkage. Documentation here
How can it be referenced, if it's hidden?
It can't be, which is what you are being warned about. E.g. the linktime warning:
hidden symbol `stat' in /usr/lib/libc_nonshared.a(stat.oS) is referenced by DSO
is telling you that a DSO in the linkage references the symbol
the linker can locate a definition of
but (obviously) that definition is not in the DSO that references it
and cannot be referenced from that DSO, because it is hidden.
You get this problem if the problem DSO has not been built correctly for use as a DSO. See this example and follow the follow-ups for the solution.
Continued for OP's followups
If hidden symbol is already referenced by some DSO, then why the problem is with DSO?
The linker is saying:
X contains a reference to symbol
S. I can find a definition of symbol
S is another linked module
but that definition will not be available to satisfy the reference in
X dynamically (i.e. at runtime) because
S has hidden linkage in
I can confirm that the problem comes with a non-shared object [...][but] I don't explicitly hide those symbols in my non-shared object.
You may not have explicitly marked any symbols hidden in the non-shared object. Depending on how it was built, symbols may be hidden by default unless explicitly marked otherwise.
Say the non-shared object is
libnonshared.a and the allegedly hidden symbol is
objdump -t libnonshared.a
to get info about the symbols in
libnonshared.a. In the output, look for the entry for
foo. Does it contain the tag
.hidden? - e.g.
0000000000000000 g F .text 000000000000000b .hidden foo
This entry says that
foo is a global symbol (marked
g - that's why the linker is able to see it) but it's hidden for dynamic linkage.
If this turns out to be the case then you need to go and fix the build of
libnonshared.a so that it doesn't hide
If not, then I'm stumped.