Merge pull request #7348 from thufschmitt/dont-use-vlas

Remove the usage of VLAs in the code

(cherry picked from commit ac4431e9d016e62fb5dc9ae36833bd0c6cdadeec)
Change-Id: Ifbf5fbfc2e27122362a2aaea4b62c7cf3ca46b1a

1 files changed, 16 insertions, 0 deletions

diff --git a/src/libexpr/primops.hh b/src/libexpr/primops.hh
index 930e7f32a..45486608f 100644
--- a/src/libexpr/primops.hh
+++ b/src/libexpr/primops.hh
@@ -8,6 +8,22 @@
 
 namespace nix {
 
+/**
+ * For functions where we do not expect deep recursion, we can use a sizable
+ * part of the stack a free allocation space.
+ *
+ * Note: this is expected to be multiplied by sizeof(Value), or about 24 bytes.
+ */
+constexpr size_t nonRecursiveStackReservation = 128;
+
+/**
+ * Functions that maybe applied to self-similar inputs, such as concatMap on a
+ * tree, should reserve a smaller part of the stack for allocation.
+ *
+ * Note: this is expected to be multiplied by sizeof(Value), or about 24 bytes.
+ */
+constexpr size_t conservativeStackReservation = 16;
+
 struct RegisterPrimOp
 {
     typedef std::vector<PrimOp> PrimOps;