[PATCH 1/2] target/s390x: Fix DR/D INT64_MIN / -1 host crash

[Ilya Leoshkevich <iii@linux.ibm.com>]

helper_divs32() divides the 64-bit dividend by the 32-bit divisor as a 64-bit
host operation, guarding only against a zero divisor. INT64_MIN / -1 therefore
overflows the host division before the representability check runs; on hosts
that trap this, QEMU is killed with SIGFPE instead of raising the
fixed-point-divide exception the guest expects:

    qemu-s390x: QEMU internal SIGFPE {code=INTDIV, addr=...}

helper_divs64() already guards the same case; add the missing check to
helper_divs32().

Reported-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Fixes: b4e2bd3563af ("target-s390: Send signals for divide")
Cc: qemu-stable@nongnu.org
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
 target/s390x/tcg/int_helper.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/target/s390x/tcg/int_helper.c b/target/s390x/tcg/int_helper.c
index fbda396f5b4..5aedd1405bf 100644
--- a/target/s390x/tcg/int_helper.c
+++ b/target/s390x/tcg/int_helper.c
@@ -39,7 +39,8 @@ uint64_t HELPER(divs32)(CPUS390XState *env, int64_t a, int64_t b64)
     int32_t b = b64;
     int64_t q, r;
 
-    if (b == 0) {
+    /* Catch divide by zero, and non-representable quotient (MIN / -1).  */
+    if (b == 0 || (b == -1 && a == (1ll << 63))) {
         tcg_s390_program_interrupt(env, PGM_FIXPT_DIVIDE, GETPC());
     }
 
-- 
2.55.0