diff options
Diffstat (limited to 'winsup/cygwin/dcrt0.cc')
| -rw-r--r-- | winsup/cygwin/dcrt0.cc | 35 |
1 files changed, 18 insertions, 17 deletions
diff --git a/winsup/cygwin/dcrt0.cc b/winsup/cygwin/dcrt0.cc index f021f0281..673f87a15 100644 --- a/winsup/cygwin/dcrt0.cc +++ b/winsup/cygwin/dcrt0.cc @@ -1250,6 +1250,13 @@ cygwin__cxa_atexit (void (*fn)(void *), void *obj, void *dso_handle) return __cxa_atexit (fn, obj, dso_handle); } +/* This function is only called for applications built with Cygwin versions + up to 1.7.32. Starting with 1.7.33, atexit is a statically linked function + inside of libcygwin.a. The reason is that the old method to fetch the + caller return address is unreliable given GCCs ability to perform tail call + elimination. For the details, see the below comment. + The atexit replacement is defined in libcygwin.a to allow reliable access + to the correct DSO handle. */ extern "C" int cygwin_atexit (void (*fn) (void)) { @@ -1259,7 +1266,7 @@ cygwin_atexit (void (*fn) (void)) #ifdef __x86_64__ /* x86_64 DLLs created with GCC 4.8.3-3 register __gcc_deregister_frame as atexit function using a call to atexit, rather than __cxa_atexit. - Due to GCC's aggressive optimizing, cygwin_atexit doesn't get the correct + Due to GCC's tail call optimizing, cygwin_atexit doesn't get the correct return address on the stack. As a result it fails to get the HMODULE of the caller and thus calls atexit rather than __cxa_atexit. Then, if the module gets dlclosed, __cxa_finalize (called from dll_list::detach) can't @@ -1268,22 +1275,16 @@ cygwin_atexit (void (*fn) (void)) module is already unloaded and the __gcc_deregister_frame function not available ==> SEGV. - Workaround: If dlls.find fails, and _my_tls.retaddr is a Cygwin function - address, and fn is a function address in another DLL, try to find the - dll entry of the DLL containing fn. Then check if fn is the address of - the DLLs __gcc_deregister_frame function. If so, proceed by calling - __cxa_atexit, otherwise call atexit. */ - extern void *__image_base__; - if (!d - && (uintptr_t) _my_tls.retaddr () >= (uintptr_t) &__image_base__ - && (uintptr_t) _my_tls.retaddr () <= (uintptr_t) &_cygheap_start - && (uintptr_t) fn > (uintptr_t) &_cygheap_start) - { - d = dlls.find ((void *) fn); - if (d && (void *) GetProcAddress (d->handle, "__gcc_deregister_frame") - != fn) - d = NULL; - } + This also occurs for other functions. + + Workaround: If dlls.find fails, try to find the dll entry of the DLL + containing fn. If that works, proceed by calling __cxa_atexit, otherwise + call atexit. + + This *should* be sufficiently safe. Ultimately, new applications will + use the statically linked atexit function though, as outlined above. */ + if (!d) + d = dlls.find ((void *) fn); #endif res = d ? __cxa_atexit ((void (*) (void *)) fn, NULL, d->handle) : atexit (fn); return res; |