Fix SIGFPE from integer overflow during division

On some architectures (like x86_64 or i686, but not ARM for example)
overflow during integer division causes a crash due to SIGFPE.
Reproduces on a 64-bit system with:

    nix-instantiate --eval -E '(-9223372036854775807 - 1) / -1'

The only way this can happen is when the smallest possible integer is
divided by -1, so just special-case that.

1 files changed, 9 insertions, 3 deletions

diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 5ba9830423..4398cc951d 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -1516,10 +1516,16 @@ static void prim_div(EvalState & state, const Pos & pos, Value * * args, Value &
     NixFloat f2 = state.forceFloat(*args[1], pos);
     if (f2 == 0) throw EvalError(format("division by zero, at %1%") % pos);
 
-    if (args[0]->type == tFloat || args[1]->type == tFloat)
+    if (args[0]->type == tFloat || args[1]->type == tFloat) {
         mkFloat(v, state.forceFloat(*args[0], pos) / state.forceFloat(*args[1], pos));
-    else
-        mkInt(v, state.forceInt(*args[0], pos) / state.forceInt(*args[1], pos));
+    } else {
+        NixInt i1 = state.forceInt(*args[0], pos);
+        NixInt i2 = state.forceInt(*args[1], pos);
+        /* Avoid division overflow as it might raise SIGFPE. */
+        if (i1 == std::numeric_limits<NixInt>::min() && i2 == -1)
+            throw EvalError(format("overflow in integer division, at %1%") % pos);
+        mkInt(v, i1 / i2);
+    }
 }