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      1 /* Test if definedness of rflags values is correctly propagated in and out
      2    of a signal handler.  Note that actually only the propagation of the
      3    overflow and sign flags is tested.
      4 
      5    This test must use alarm(2) to trigger the signal and not kill(2) as other
      6    tests do because in the latter case the signal is actually delivered after
      7    the syscall finished.  This means that Valgrind had to save a correct carry
      8    flag value (indicating if the syscall succeeded) in the rflags.  This save
      9    operation unfortunately makes all rflags initialised (due to imprecise
     10    simulation). */
     11 
     12 #include <assert.h>
     13 #include <signal.h>
     14 #include <stdio.h>
     15 #include <stdlib.h>
     16 #include <unistd.h>
     17 #include <sys/regset.h>
     18 #include <sys/syscall.h>
     19 #include <sys/ucontext.h>
     20 
     21 #define OBIT(rflags) (!!((rflags) & (1 << 11)))
     22 #define SBIT(rflags) (!!((rflags) & (1 << 7)))
     23 
     24 static siginfo_t si;
     25 static ucontext_t uc;
     26 
     27 void break_out(void);
     28 
     29 static void sighandler(int sig, siginfo_t *sip, void *arg)
     30 {
     31    ucontext_t *ucp = (ucontext_t *) arg;
     32 
     33    si = *sip;
     34    uc = *ucp;
     35 
     36    /* Break out of the endless loop. */
     37    *(uintptr_t*)&ucp->uc_mcontext.gregs[REG_RIP] = (uintptr_t)break_out;
     38 }
     39 
     40 int main(void)
     41 {
     42    struct sigaction sa;
     43    long rflags;
     44    int x1;
     45 
     46    /* Uninitialised, but we know px[0] is 0x0. */
     47    int *px = malloc(sizeof(*px));
     48    x1 = px[0] + 1;
     49 
     50    sa.sa_sigaction = sighandler;
     51    sa.sa_flags = SA_SIGINFO;
     52    if (sigfillset(&sa.sa_mask)) {
     53       perror("sigfillset");
     54       return 1;
     55    }
     56    if (sigaction(SIGALRM, &sa, NULL)) {
     57       perror("sigaction");
     58       return 1;
     59    }
     60 
     61    alarm(2);
     62 
     63    __asm__ __volatile__(
     64       /* Set overflow and sign flags. */
     65       "movl   %[x1], %%edx\n"
     66       "addl   $0x7fffffff, %%edx\n"
     67 
     68       /* Loopity loop, this is where the SIGALRM is triggered. */
     69       "1:\n"
     70       "jmp    1b\n"
     71 
     72       "break_out:\n"
     73       "pushfq\n"
     74       "popq   %%rdx\n"
     75       : "=d" (rflags)
     76       : [x1] "m" (x1)
     77       : "cc", "memory");
     78 
     79    /* Check that the overflow and sign flags are uninitialised.
     80 
     81       Note: This actually fails because the rflags are only approximate
     82       (always initialised) in the signal handler. */
     83    if (!OBIT(uc.uc_mcontext.gregs[REG_RFL]) ||
     84        !SBIT(uc.uc_mcontext.gregs[REG_RFL]))
     85       assert(0);
     86 
     87    /* Check that the overflow and sign flags are uninitialised. */
     88    if (!OBIT(rflags) || !SBIT(rflags))
     89       assert(0);
     90 
     91    return 0;
     92 }
     93 
     94