ptrace/select/signal errno weirdness

Brian Wellington (bwelling@xbill.org)
Thu, 15 Aug 2002 15:16:47 -0700 (PDT)


When sending a SIGINT to a ptraced process (run under gdb), an interrupted
select() call returns with errno==514. linux/include/linux/errno.h says:

/* Should never be seen by user programs */
#define ERESTARTSYS 512
#define ERESTARTNOINTR 513
#define ERESTARTNOHAND 514 /* restart if no handler.. */
#define ENOIOCTLCMD 515 /* No ioctl command */

As gdb is a user program, and the printf is printing it, there's something
wrong. This might be due to a problem in gdb, but the fact that the errno
is being seen in userspace seems bad.

A simple test program is included. To test, build and run it under gdb.
Hit ^C to get back to the gdb prompt, and enter 'signal SIGINT' to send a
SIGINT.

This has been reproduced on 2.4.18 (the Red Hat 7.3 errata kernel) and
2.4.19 (built from scratch).

Brian

----
#include <errno.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/select.h>
#include <sys/signal.h>

void
printsig(int sig) {
fprintf(stderr, "got sig %d\n", sig);
}

int
main(int argc, char **argv) {
int n;
struct sigaction sa;
memset(&sa, 0, sizeof sa);
sa.sa_handler = printsig;
n = sigaction(SIGINT, &sa, NULL);
if (n < 0) {
fprintf(stderr, "sigaction: %s\n", strerror(errno));
exit(1);
}
n = select(0, NULL, NULL, NULL, NULL);
if (n < 0) {
fprintf(stderr, "select: %s\n", strerror(errno));
exit(1);
}
exit(0);
}

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