[SOL] Allocate less space on stack for drift sort (anza-xyz#127)

Author: LucasSte

compiler/rustc_target/src/target_features.rs

@@ -649,8 +649,11 @@ static WASM_FEATURES: &[(&str, Stability, ImpliedFeatures)] = &[
 const BPF_FEATURES: &[(&str, Stability, ImpliedFeatures)] =
     &[("alu32", Unstable(sym::bpf_target_feature), &[])];
 
-const SBF_FEATURES: &[(&str, Stability, ImpliedFeatures)] =
-    &[("alu32", Unstable(sym::sbf_target_feature), &[]), ("static-syscalls", Stable, &[])];
+const SBF_FEATURES: &[(&str, Stability, ImpliedFeatures)] = &[
+    ("alu32", Unstable(sym::sbf_target_feature), &[]),
+    ("static-syscalls", Stable, &[]),
+    ("dynamic-frames", Stable, &[]),
+];
 
 const CSKY_FEATURES: &[(&str, Stability, ImpliedFeatures)] = &[
     // tidy-alphabetical-start

library/core/Cargo.toml

@@ -44,4 +44,5 @@ check-cfg = [
     'cfg(target_has_reliable_f128_math)',
     'cfg(target_family, values("solana"))',
     'cfg(target_arch, values("sbf"))',
+    'cfg(target_feature, values("dynamic-frames"))',
 ]

library/core/src/slice/sort/stable/mod.rs

@@ -118,7 +118,18 @@ fn driftsort_main<T, F: FnMut(&T, &T) -> bool, BufT: BufGuard<T>>(v: &mut [T], i
 
     // For small inputs 4KiB of stack storage suffices, which allows us to avoid
     // calling the (de-)allocator. Benchmarks showed this was quite beneficial.
-    let mut stack_buf = AlignedStorage::<T, 4096>::new();
+    let mut stack_buf;
+    #[cfg(any(target_feature = "dynamic-frames", not(target_family = "solana")))]
+    {
+        stack_buf = AlignedStorage::<T, 4096>::new();
+    }
+
+    #[cfg(all(target_family = "solana", not(target_feature = "dynamic-frames")))]
+    {
+        // Allocating 4096 bytes on SBPFv0 overflows the stack
+        stack_buf = AlignedStorage::<T, 2048>::new();
+    }
+
     let stack_scratch = stack_buf.as_uninit_slice_mut();
     let mut heap_buf;
     let scratch = if stack_scratch.len() >= alloc_len {