* Using dlmope/dlopem with RTLD_GLOBAL
[not found] <14297fb9-70cb-42b1-a477-6fb68c03ff64@Spark>
@ 2023-02-13 9:23 ` Nima Hamidi
2023-02-13 10:29 ` Florian Weimer
0 siblings, 1 reply; 4+ messages in thread
From: Nima Hamidi @ 2023-02-13 9:23 UTC (permalink / raw)
To: libc-help
[-- Attachment #1: Type: text/plain, Size: 4552 bytes --]
Hello all,
I’m trying to dlmopen a shared library which in turn dlopen’s another shared library with RTLD_GLOBAL flag set. On some platforms, it works as I expect it, but on some other platforms it crashes. Here is the simplest example I could make to show that crash:
I create a docker container containing my example using:
////////////////////////////////////////////////////////////
docker run --rm -it ubuntu:devel bash
apt-get update
apt install g++-10
cd ~
cat >a.cpp <<EOF
// a.cpp
#include <iostream>
#include <dlfcn.h>
using namespace std;
int main () {
void * handle = nullptr;
bool mopen = true;
if (mopen) {
cout << "mopening libb.so" << endl;
handle = dlmopen(LM_ID_NEWLM, "libb.so", RTLD_NOW | RTLD_LOCAL);
} else {
cout << "opening libb.so" << endl;
handle = dlopen("libb.so", RTLD_NOW | RTLD_LOCAL);
}
void (*bfunc)();
*(void**)(&bfunc) = dlsym(handle, "bfunc");
bfunc();
return 0;
}
EOF
cat >b.cpp <<EOF
// b.cpp
#include <iostream>
#include <dlfcn.h>
using namespace std;
extern "C" void bfunc() {
cout << "bfunc in b.cpp is being called..." << endl;
void * handle = dlopen("libc.so", RTLD_NOW | RTLD_GLOBAL);
//void * handle = dlopen("libc.so", RTLD_NOW | RTLD_LOCAL);
void (*cfunc)();
*(void**)(&cfunc) = dlsym(handle, "cfunc");
cfunc();
}
EOF
cat >c.cpp <<EOF
// c.cpp
#include <iostream>
using namespace std;
extern "C" void cfunc() {
cout << "cfunc in c.cpp is being called..." << endl;
}
EOF
g++-10 a.cpp -o a -ldl -Wl,-rpath `pwd`
g++-10 b.cpp -o libb.so -shared -fPIC -ldl -Wl,-rpath `pwd`
g++-10 c.cpp -o libc.so -shared -fPIC
////////////////////////////////////////////////////////////
Finally, when I run LD_DEBUG=1 ./a, it crashes with the following log:
902: symbol=_ZNSt8ios_base4InitD1Ev; lookup in file=/root/libb.so [1]
902: symbol=_ZNSt8ios_base4InitD1Ev; lookup in file=/lib/aarch64-linux-gnu/libstdc++.so.6 [1]
902: symbol=__cxa_finalize; lookup in file=/root/libb.so [1]
902: symbol=__cxa_finalize; lookup in file=/lib/aarch64-linux-gnu/libstdc++.so.6 [1]
902: symbol=__cxa_finalize; lookup in file=/lib/aarch64-linux-gnu/libc.so.6 [1]
902: symbol=_ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc; lookup in file=/root/libb.so [1]
902: symbol=_ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc; lookup in file=/lib/aarch64-linux-gnu/libstdc++.so.6 [1]
902: symbol=_ZNSolsEPFRSoS_E; lookup in file=/root/libb.so [1]
902: symbol=_ZNSolsEPFRSoS_E; lookup in file=/lib/aarch64-linux-gnu/libstdc++.so.6 [1]
902: symbol=__cxa_atexit; lookup in file=/root/libb.so [1]
902: symbol=__cxa_atexit; lookup in file=/lib/aarch64-linux-gnu/libstdc++.so.6 [1]
902: symbol=__cxa_atexit; lookup in file=/lib/aarch64-linux-gnu/libc.so.6 [1]
902: symbol=_ZNSt8ios_base4InitC1Ev; lookup in file=/root/libb.so [1]
902: symbol=_ZNSt8ios_base4InitC1Ev; lookup in file=/lib/aarch64-linux-gnu/libstdc++.so.6 [1]
902: symbol=__gmon_start__; lookup in file=/root/libb.so [1]
902: symbol=__gmon_start__; lookup in file=/lib/aarch64-linux-gnu/libstdc++.so.6 [1]
902: symbol=__gmon_start__; lookup in file=/lib/aarch64-linux-gnu/libc.so.6 [1]
902: symbol=__gmon_start__; lookup in file=/lib/ld-linux-aarch64.so.1 [0]
902: symbol=__gmon_start__; lookup in file=/lib/aarch64-linux-gnu/libm.so.6 [1]
902: symbol=__gmon_start__; lookup in file=/lib/aarch64-linux-gnu/libgcc_s.so.1 [1]
902: symbol=__gmon_start__; lookup in file=/root/libc.so [1]
902: symbol=__gmon_start__; lookup in file=/lib/aarch64-linux-gnu/libstdc++.so.6 [1]
902: symbol=__gmon_start__; lookup in file=/lib/aarch64-linux-gnu/libc.so.6 [1]
902: symbol=__gmon_start__; lookup in file=/lib/aarch64-linux-gnu/libm.so.6 [1]
902: symbol=__gmon_start__; lookup in file=/lib/ld-linux-aarch64.so.1 [0]
902: symbol=__gmon_start__; lookup in file=/lib/aarch64-linux-gnu/libgcc_s.so.1 [1]
Segmentation fault
The libc version that I’m using is 2.36 as outputted by
$ ldd --version
ldd (Ubuntu GLIBC 2.36-0ubuntu4) 2.36
Copyright (C) 2022 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
Written by Roland McGrath and Ulrich Drepper
The error won’t happen if I dlopen with RTLD_LOCAL in b.cpp rather than RTLD_GLOBAL. I would appreciate any help on what I’m doing wrong here.
Best,
Nima
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