Bug in dlopen() (or following) code in Cygwin1.dll v 1.5.19-4

Thu Mar 9 15:56:00 GMT 2006

Hi,
With the release of Cygwin-1.5.19-4, we have had
silent crashes of the Computer Algebra System SAGE at
startup. I have traced these to an invalid memory
access in pthread_key_create() which SHOULD be caught
and processed by the fault handler in
verifyable_object_isvalid(). However, the program
always dies in the return from this routine.
After some research, I believe that the crash occurs
when loading a dll via
 dlopen() and the cygwin dll intialization code calls
 dll:init() which calls
 run_ctors() which calls (eventually) 
 pthread::once() which calls 
 init_routine() and init_routine() happens to be
fc_key_init().
 fc_key_init() sets up the pthread_key_t object, calls
 _sigfe_pthread_key_create() which jumps into 
 pthread_key_create() which calls 
 verifyably_object_isvalid() and we crash.
------------------------------------------------
I think that this is happening if one dlopen()s a dll
that is created with -lstdc++. 
If ANY dll which is created with -lstdc++ is LINKED
into the executable, everything gets initialized
properly and pthread_key_create() catches the SIGSEGV
and continues
normally.
Here is a simplified test to show what is going on:
------Simple script to put everything together:
#!/bin/sh
#NOTE: add -DHARDLINKTEST to ct.c compile to get
# a non-crashing exe
#1st dll to be dlopen()ed only:
gcc -DDEBUG -gstabs+ -g3 -fno-strict-aliasing -Wall -c
CrashTest.cc -o CrashTest.o
g++ -shared ./CrashTest.o -o CrashTest.dll -lstdc++
#2nd dll to linked directly by exe
gcc -DDEBUG -gstabs+ -g3 -fno-strict-aliasing -Wall -c
Crash2.cc -o Crash2.o
g++ -shared -Wl,--out-implib=libCrash2.dll.a
-Wl,--export-all-symbols -Wl,--enable-auto-import
-Wl,--whole-archive Crash2.o -Wl,--no-whole-archive -o
Crash2.dll -lstdc++
#3rd dll without -lstdc++
gcc -DDEBUG -gstabs+ -g3 -fno-strict-aliasing -Wall -c
OK.cc -o OK.o
g++ -shared ./OK.o -o OK.dll -lstdc++
#exe test program
gcc -DDEBUG -gstabs+ -g3 ct.c -o ct.exe -L./ -lCrash2
------Code for exe (ct.c):
#include <windows.h>
#include <winbase.h>
#include <stdio.h>
extern void test(); /* test function in dlls */
void TestLinked(char* pszdll);
void TestLoad(char* pszdll);
int main(int argc, char** argv)
{
 int ret;
/* NOTE: -DHARDLINKTEST in makefile if you want this 
 to run
 */
#ifdef HARDLINKTEST
 TestLinked("./Crash2.dll");
#endif
 TestLoad("./OK.dll");
 TestLoad("./CrashTest.dll");
 printf("THAT'S ALL FOLKS\n");
}
#ifdef HARDLINKTEST
void TestLinked(char* pszdll)
{
 printf("Testing build time linked %s\n", pszdll);
 _Z4testv(); /* call test() in dll - real code
would
 have __declspec(dllexport), etc and
 extern "C" syntactic sugar
 */
}
#endif
typedef UINT (CALLBACK* LPFNDLLFUNC1)(DWORD,UINT);
void TestLoad(char* pszdll)
{
 printf("dlopening %s\n", pszdll);
 HANDLE hDLL = (HANDLE)dlopen(pszdll);
 if(hDLL){
 printf("Getting proc address for test\n");
 LPFNDLLFUNC1 lpfnDllFunc1 =
(LPFNDLLFUNC1)GetProcAddress(hDLL,
 
 "_Z4testv");
 if (!lpfnDllFunc1){
 // handle the error
 printf("Failed to get the function: %d\n",
GetLastError());
 FreeLibrary(hDLL);
 return;
 }
 else {
 // call the function
 printf("Calling test\n");
 UINT uReturnVal = lpfnDllFunc1(0,0);
 printf("Back from test\n");
 }
 }
 else
 printf("Error %d dlopening %s\n",
GetLastError(), pszdll);
}
------Code for 1st dll (CrashTest.cc):
#include <iostream>
using namespace std;
void test()
{
 cout << "\tCRASHTEST: This is a test." << endl
<< "Did you crash?" << endl;
}
------Code for 2nd dll (Crash2.cc):
#include <iostream>
#include "Crash2.h"
using namespace std;
void test()
{
 cout << "\tCRASH2: This is a test." << endl <<
"Did you crash?" << endl;
}
------Code for 3rd dll (OK.c):
#include <windows.h>
#include <stdio.h>
void test()
{
 printf("\tOK: This is a test.\n");
}
----------------------------------------------
NOTE: I have also tested all of this with 
 __declspec(dllexport) and
 __declspec(dllimport) 
 and everything works exactly the same
Thanks,
Gary
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