Reading libstdc++ version at runtime

Question

My application is affected by a bug in older versions of libstdc++ in a rather serious data-lossy way. The remedies of how to select the right library version with -rpath or LD_LIBRARY_PATH are known, but not reliable to changes in deployment and build. After being bitten more than once myself I would like to stop the suffering and introduce a runtime-check for a sufficiently new version of libstdc++. How can I access the version in order to print a big fat warning message in case of the deployment failing to use the right version. Note that I need the minor version libstdc++.so.6.0.25 a.k.a. GLIBCXX_3.4.25 that comes with gcc 8.

might be helpful: https://stackoverflow.com/questions/10516041/check-gcc-version-in-runtime — BladeMight, Oct 24 '18 at 17:18
you can define the some variable with result from `g++ -dumpversion`, and then check for it in code. — BladeMight, Oct 24 '18 at 17:22
Unfortunately the gcc version doesn't help. In fact we usually build with a non-default gcc 8.2, but that simply links `libstdc++.so.6` - which also happens to be satisfied by the system `libstdc++.so.6.0.22` coming from system gcc 6.3.0. — Zulan, Oct 24 '18 at 17:22
You can check which library is being used by `gcc -lstdc++` and later check it by `strings` command + `grep GLIBCXX`, and find the `GLIBCXX_3.4.25` from it. — BladeMight, Oct 24 '18 at 17:26
@BladeMight That's not a runtime check that the program itself can perform in any easy way. — nos, Oct 24 '18 at 17:42
On Linux you can check contents of `/proc/self/maps` from the running process for incorrect libraries. Not trivial but not very hard. — dewaffled, Oct 24 '18 at 22:24
Also see https://stackoverflow.com/questions/10354636/how-do-you-find-what-version-of-libstdc-library-is-installed-on-your-linux-mac — Mihai8, Oct 27 '18 at 09:23

score 5 · Accepted Answer · answered Oct 28 '18 at 11:25

Here is a linux program that simply lists the absolute real paths of the DSOs it has loaded (as enumerated by dl_iterate_phdr) that are accessible files. (All linux programs load linux-vdso.so, which isn't actually a file).

main.cpp

#include <link.h>
#include <climits>
#include <cstdlib>
#include <string>
#include <vector>
#include <iostream>

int
get_next_SO_path(dl_phdr_info *info, size_t, void *p_SO_list)
{
    auto & SO_list =
        *static_cast<std::vector<std::string> *>(p_SO_list);
    auto p_SO_path = realpath(info->dlpi_name,NULL);
    if (p_SO_path) {
        SO_list.emplace_back(p_SO_path);
        free(p_SO_path);
    }
    return 0;
}

std::vector<std::string>
get_SO_realpaths()
{
    std::vector<std::string> SO_paths;
    dl_iterate_phdr(get_next_SO_path, &SO_paths);
    return SO_paths;
}


int main()
{
    auto SO_paths = get_SO_realpaths();
    for (auto const & SO_path : SO_paths) {
        std::cout << SO_path << std::endl;
    }
    return 0;
}

Which for me runs like:

$ g++ -Wall -Wextra main.cpp && ./a.out
/usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.25
/lib/x86_64-linux-gnu/libgcc_s.so.1
/lib/x86_64-linux-gnu/libc-2.27.so
/lib/x86_64-linux-gnu/libm-2.27.so
/lib/x86_64-linux-gnu/ld-2.27.so

Live demo

As you see, the full version appears. With a bit of filename parsing, you can take it from there. Getting the whole DSO list, as per get_SO_realpaths, before looking for any libstdc++ would let you detect, if you want, the freak possibility of more than one libstdc++ being loaded.

I admit this is a more complex solution than I had hoped for, but fairly elegant never the less. — Zulan, Oct 30 '18 at 16:54

Reading libstdc++ version at runtime

1 Answers1