#1816: segfaults on 64bit systems when build with c99 --------------------------------+------------------------------------------- Reporter: physik@… | Owner: Type: defect | Status: new Priority: unset | Milestone: Component: Cactus | Version: ET_2014_05 Keywords: | --------------------------------+------------------------------------------- I recently encountered a segfault in ScheduleInterface.c, more precisely in the function
static int CCTKi_ScheduleCallFunction(void *function, t_attribute *attribute, t_sched_data *data) { /* find the timer for this function and this schedule bin */ t_timer *timer = attribute->timers; while (timer && strcmp(timer->schedule_bin, data->schedule_bin)) { timer = timer->next; }
Running in the debugger revealed that timer->schedule_bin pointed to an invalid address. Curiously, it had the top 33 (33 not a typo) bits all set. Taking the lowest 32 bits gave a valid address which pointed to a reasonable string "CCTK_INITIAL". This suggests a 32/64 bit issue. The pointer timer->schedule_bin seems to be initialized in the same function using strdup:
timer->schedule_bin = strdup (where);
strdup is not part of the c99 standard, but only Posix. Compiling with gcc --std=c99 means it is not defined in <string.h>. This means the compiler treats the occurrence of strdup as an implicit function declaration, and assumes it returns int. Thus, it will do an implicit conversion of the result from int to char*. If the highest bit of the int was set, this resulted in a 64 bit pointer with all 32 high bits set (I checked with a small test code). When the address returned by the actual strdup code linked from glibc has the top 33 bits zero, the conversion yields the correct results. Therefore, the problem is hard to reproduce, it only occurred with a test case almost exhausting my workstations memory, but frustratingly not small tests.
After this, I also found compiler warnings for ScheduleInterface.c of the type
implicit declaration of function ‘strdup’ [-Wimplicit-function- declaration] and assignment makes pointer from integer without a cast [-Wint-conversion]
Switching from --std=c99 to --std=gnu99 fixed the problem for now. However, this is a bug that might affect many users since the code compiles with --std=c99 and the compiler warnings are hidden within the thousands of other compiler warnings the ET code generates.
Also, a quick grep revealed many occurrences of strdup, although some of them where redefined as Util_Strdup. The rest might lead to segfaults on 64 bit systems with std=c99.
My findings concern the Wheeler release, I haven't had time to check the development version.