On 2020-11-24 19:02 +0000, Kacvinsky, Tom via Gcc-help wrote:
> This code
>
> #include <string>
> #include <istream>
> #include <iostream>
> #include <vector>
>
> typedef std::vector<unsigned char> Signature;
>
> namespace foo {
> bool bar (const std::string& input,
> const Signature& signature,
> std::istream& key)
> {
> return true;
> }
> }
>
> when compiled with
>
> g++ -fPIC -o global_noans.so -shared -static-libgcc -static-libstdc++ -Wl,-
> h,global.so -fuse-ld=gold global_noans.cpp
>
> produces this nm output
>
> 0000000000082745 T
> _ZN3foo3barERKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEERKSt6vectorI
> hSaIhEERSi
>
> Notice how it is a global symbol?
>
> On the other hand, this code#include <string>
> #include <istream>
> #include <iostream>
> #include <vector>
>
> typedef std::vector<unsigned char> Signature;
>
> namespace foo {
> namespace {
> bool bar(const std::string& input,
> const Signature& signature,
> std::istream& key)
> {
> return true;
> }
> }
> }
>
> when compiled with
>
> g++ -fPIC -o global.so -shared -static-libgcc -static-libstdc++ -Wl,-
> h,global.so -fuse-ld=gold global.cpp
>
> produces this nm output
>
> 00000000000826b5 t
> _ZN3foo12_GLOBAL__N_13barERKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcE
> EERKSt6vectorIhSaIhEERSi
>
> And now we note the symbolis local. I tried building the shared library with
> a -Wl,--version-script=global.map, where global.map
> is set up to make the symbol glocal instead of local, and that did not work.
> I also tried compiling the source code with
>
> void __attribute__ ((visibility ("default")))
>
> but that made no difference, either, in the anonymous namespace symbol being
> lobal. I have pinged the binutils list and they said
> this might be a g++ version issue (I am using GCC 8.3.0 with binutils 2.34,
> gold linker). If this is a g++ issues, I am assuming the issue
> is anonymous name spaces make the symbol local, but if that isn't the cause,
> I'll got back to the binutils folks. I am also going to try
> a later version of GCC and binutils.
The standard says ([basic.link] p4):
> An unnamed namespace or a namespace declared directly or indirectly within an
> unnamed namespace has internal linkage. All other namespaces have external
> linkage. A name having namespace scope that has not been given internal
> linkage above has the same linkage as the enclosing namespace if it is the
> name of
> (4.1) a variable; or
> (4.2) a function; or
> ...
--
Xi Ruoyao <xry111@xxxxxxxxxxxxxxxx>
School of Aerospace Science and Technology, Xidian University
