r9 is used to determine whether syscall restarting must be performed or
not. Unfortunately, r9 is never set to zero in the non-syscall path,
and r9 is on top of that a callee-saved register which can be set to
non-zero by the C functions that are called during IRQ handling.
This means that if r10 (used for the syscall return value) is one of the
-ERESTART* values when a hardware interrupt occurs which leads to a
signal being delivered to the process, the kernel will "restart" a
syscall which never occurred. This will lead to the PC being moved back
by 2 on return to user space.
Fix the problem by setting r9 to zero in the interrupt path.
Test case (should loop forever but ends up executing the break 8 trap
instruction):
#include <signal.h>
#include <stdlib.h>
#include <sys/time.h>
void f(int n)
{
register int r9 asm ("r9") = 1;
register int r10 asm ("r10") = n;
__asm__ __volatile__(
"ba 1f \n"
"nop \n"
"break 8 \n"
"1: ba . \n"
"nop \n"
:
: "r" (r9), "r" (r10)
: "memory");
}
void handler1(int sig) { }
int main(int argc, char *argv[])
{
struct itimerval t1 = { .it_value = {1} };
signal(SIGALRM, handler1);
setitimer(ITIMER_REAL, &t1, NULL);
f(-513); /* -ERESTARTNOINTR */
return 0;
}
Signed-off-by: Rabin Vincent <rabin@rab.in>
Signed-off-by: Jesper Nilsson <jespern@axis.com>
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