[Qemu-devel] [PATCH] Alpha bug fix: overflow condition for sublv and subqv

[Tristan Gingold]

The conditions to detect overflow in sub operations was wrong.

This patch is necessary to boot Tru64.

Signed-off-by: Tristan Gingold <address@hidden>
---
 target-alpha/op_helper.c |   20 ++++++++++----------
 tests/alpha/Makefile     |    3 +++
 tests/alpha/test-ovf.c   |   29 +++++++++++++++++++++++++++++
 3 files changed, 42 insertions(+), 10 deletions(-)
 create mode 100644 tests/alpha/test-ovf.c

diff --git a/target-alpha/op_helper.c b/target-alpha/op_helper.c
index 7ad1b3d..3c95e98 100644
--- a/target-alpha/op_helper.c
+++ b/target-alpha/op_helper.c
@@ -158,22 +158,22 @@ uint64_t helper_addlv (uint64_t op1, uint64_t op2)
 
 uint64_t helper_subqv (uint64_t op1, uint64_t op2)
 {
-    uint64_t tmp = op1;
-    op1 -= op2;
-    if (unlikely(((~tmp) ^ op1 ^ (-1ULL)) & ((~tmp) ^ op2) & (1ULL << 63))) {
-        helper_excp(EXCP_ARITH, EXCP_ARITH_OVERFLOW);
+    uint64_t res;
+    res = op1 - op2;
+    if (unlikely((op1 ^ op2) & (res ^ op1) & (1ULL << 63))) {
+        helper_excp(EXCP_GEN_ARITH, EXCP_ARITH_OVERFLOW);
     }
-    return op1;
+    return res;
 }
 
 uint64_t helper_sublv (uint64_t op1, uint64_t op2)
 {
-    uint64_t tmp = op1;
-    op1 = (uint32_t)(op1 - op2);
-    if (unlikely(((~tmp) ^ op1 ^ (-1UL)) & ((~tmp) ^ op2) & (1UL << 31))) {
-        helper_excp(EXCP_ARITH, EXCP_ARITH_OVERFLOW);
+    uint32_t res;
+    res = op1 - op2;
+    if (unlikely((op1 ^ op2) & (res ^ op1) & (1UL << 31))) {
+        helper_excp(EXCP_GEN_ARITH, EXCP_ARITH_OVERFLOW);
     }
-    return op1;
+    return res;
 }
 
 uint64_t helper_mullv (uint64_t op1, uint64_t op2)
diff --git a/tests/alpha/Makefile b/tests/alpha/Makefile
index e4e23d2..2b1f03d 100644
--- a/tests/alpha/Makefile
+++ b/tests/alpha/Makefile
@@ -23,6 +23,9 @@ test-cmov.o: test-cond.c
 test-cmov: test-cmov.o crt.o
        $(LINK)
 
+test-ovf: test-ovf.o crt.o
+       $(LINK)
+
 check: $(TESTS)
        for f in $(TESTS); do $(SIM) $$f || exit 1; done
 
diff --git a/tests/alpha/test-ovf.c b/tests/alpha/test-ovf.c
new file mode 100644
index 0000000..01c80e7
--- /dev/null
+++ b/tests/alpha/test-ovf.c
@@ -0,0 +1,29 @@
+static long test_subqv (long a, long b)
+{
+  long res;
+
+  asm ("subq/v %1,%2,%0"
+       : "=r" (res) : "r" (a), "r" (b));
+  return res;
+}
+static struct {
+  long (*func)(long, long);
+  long a;
+  long b;
+  long r;
+} vectors[] =
+  {
+    {test_subqv, 0, 0x7d54000, 0xfffffffff82ac000L}
+  };
+
+int main (void)
+{
+  int i;
+
+  for (i = 0; i < sizeof (vectors)/sizeof(vectors[0]); i++)
+    if ((*vectors[i].func)(vectors[i].a, vectors[i].b) != vectors[i].r) {
+      write(1, "Failed\n", 7);
+    }
+  write(1, "OK\n", 3);
+  return 0;
+}
-- 
1.6.2