1.7.9: static const std::string initialization lost in child process when using fork, dlopen

[whans at web dot de]

Hello,
Â
it seems that a child process does not see the initialization of a
static const std::string variable if it is defined in a dll. Instead this corrupt variable
lead to a STATUS_ACCESS_VIOLATION.
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The following 4 example files demonstrate this behaviour:
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1) dllif.h: Â Â Â(define the dll's interface)
#include <string>
class cTestIf {
public:
 virtual std::string get() = 0;
};
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2) dll.h: Â Â Â Â(member variable t will cause the child's stackdump)
#include "dllif.h"
class cTest : public cTestIf {
public:
 static const std::string t;
 virtual std::string get() {
   return cTest::t;
 }
};
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3) dll.cpp   Â(definition of dll including initializer of t)
#include "dll.h"
const std::string cTest::t = "Test";
Â
extern "C" cTest* getTest() {
 Âreturn new cTest();
}
Â
Â
4) test.cpp  Â(fork child, load dll and print cTest::t both in parent and child)
#include <unistd.h>
#include <dlfcn.h>
#include "dllif.h"
#include <iostream>
Â
typedef cTestIf *(*tFunc)();
Â
void load(const char *p) {
 void* lib = dlopen("libdll.dll", RTLD_NOW|RTLD_GLOBAL);
 tFunc func = (tFunc)dlsym(lib, "getTest");
 cTestIf* test = func();
 std::cerr << p << ":" << test->get() << "\n";
}
Â
main() {
 Âif (fork())
   load("parent");
 Âelse {
   sleep(30); Â// keep child alive to enable attachment from gdb
   load("child");
 Â}
}
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commands used to create dll and test program:
g++ -g -c dll.cpp -o dll.o
g++ -shared -o libdll.dll dll.o
g++ -g -c test.cpp -o test.o
g++ -o test test.o -L. -ldll
Â
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./test.exe prints only 'parent:Test' - parent works as expected - and gives a
test.exe.stackdump - after 30 seconds.
Â
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an example gdb session looks like:
attach <child pid>
b load
c      (needs up to 30 seconds for return)
n
n
n
s      (step into dll's cTest::get method)
p t     (print cTest::t, _M_p seems to be corrupt)
$1 = {static npos = <optimized out>,
 _M_dataplus = {<std::allocator<char>> = {<__gnu_cxx::new_allocator<char>> = {<
No data fields>}, <No data fields>}, _M_p = 0x0}}
n
Program received signal SIGSEGV, Segmentation fault.
0x6c4b95be in cygstdc++-6!_ZNSsC1ERKSs () from /usr/bin/cygstdc++-6.dll
Â
ÂAny idea to fix or circumvent this error?

Regards,
Werner
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Attachment: test.exe.stackdump
Description: Binary data

Attachment: cygcheck.out
Description: Binary data

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