Hi
I have an application which is creating generated code blocks in memory
provided by mmap, once the application is running in the generated code
blocks, it cannot be interrupted by a SIGALRM.
In the following example I generate a code section which simply performs an
infinite loop (using an x86 jmp -2), whilst this code section is executing
I expect a SIGALRM to be raised, and the appropriate handler to be called,
however the handler never gets called, although the signal is raised.
I have run my program through strace and I see the signal being raised, but
the handler never executes, here is a snippet from strace
...
41 17854 [itimer] testbad 3680 timer_thread: 0x610ECCE8 waiting for
999 ms
927712 945566 [itimer] testbad 3680 timer_thread: timed out
102 945668 [itimer] testbad 3680 timer_thread: 0x610ECCE8 sending sig 14
45 945713 [itimer] testbad 3680 sig_send: sendsig 0x70C, pid 3680,
signal 14, its_me 1
70 945783 [itimer] testbad 3680 sig_send: Not waiting for
sigcomplete. its_me 1 signal 14
41 945824 [itimer] testbad 3680 sig_send: returning 0x0 from sending
signal 14
38 945862 [itimer] testbad 3680 timer_thread: looping
38 945900 [itimer] testbad 3680 timer_thread: 0x610ECCE8 waiting for
1000 ms
53 945953 [sig] testbad 3680 sigpacket::process: signal 14 processing
45 945998 [sig] testbad 3680 _cygtls::find_tls: sig 14
39 946037 [sig] testbad 3680 sigpacket::process: signal 14, about to
call 0x401101
40 946077 [sig] testbad 3680 setup_handler: suspending mainthread
81 946158 [sig] testbad 3680 interruptible: pc 0x3F0000, h 0x3F0000,
interruptible 0
39 946197 [sig] testbad 3680 setup_handler: couldn't
interrupt. trying again.
49 946246 [sig] testbad 3680 setup_handler: suspending mainthread
52 946298 [sig] testbad 3680 interruptible: pc 0x3F0000, h 0x3F0000,
interruptible 0
37 946335 [sig] testbad 3680 setup_handler: couldn't
interrupt. trying again.
43 946378 [sig] testbad 3680 setup_handler: suspending mainthread
...
If I replace my generated code section with a simple "for (;;);", then the
testcase works as expected.
I attach the testcase below, in order to get the expected behavior,
executing the "for(;;);" loop, simply compile in the following way
gcc -o testok.exe test.c
to produce the failing behavior, make the testcase include the generated
code section
gcc -o testbad.exe test.c -DCG_LOOP
Code is as follows
//
// test.c
//
#include <sys/time.h>
#include <signal.h>
#include <stdio.h>
#include <sys/mman.h>
static int loop(void) {
#if(CG_LOOP)
static char *mem = 0;
if(!mem) {
mem = mmap(
0,
8192,
PROT_READ|PROT_WRITE|PROT_EXEC,
MAP_PRIVATE|MAP_ANONYMOUS,
-1,
0
);
// Generated Instruction : JMP 'to here'
mem[0] = 0xeb;
mem[1] = -2;
}
goto *mem;
#else
for(;;) {}
#endif
}
static void setAlarm(int secs) {
struct itimerval new;
struct timeval time = {tv_sec:secs, tv_usec:0};
new.it_value = time;
new.it_interval = time;
setitimer(ITIMER_REAL, &new, 0);
}
static void sigalarmHandler(int signum, siginfo_t *sigInfo, void *context) {
printf("Alarm handler called\n");
setAlarm(1);
}
static void installAlarmHandler(void) {
struct sigaction SIGALRM_Handler = {{0}};
SIGALRM_Handler.sa_sigaction = sigalarmHandler;
SIGALRM_Handler.sa_flags = SA_SIGINFO;
sigfillset(&SIGALRM_Handler.sa_mask);
sigaction(SIGALRM, &SIGALRM_Handler, 0);
}
int main() {
installAlarmHandler();
setAlarm(1);
loop();
return 1;
}
--
Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
Problem reports: http://cygwin.com/problems.html
Documentation: http://cygwin.com/docs.html
FAQ: http://cygwin.com/faq/
