From f4832f2d2c2a0a4b2106458be318bb2fdf391802 Mon Sep 17 00:00:00 2001
From: Barnadrot <kbarna.drot@gmail.com>
Date: Sun, 10 May 2026 12:33:05 -0400
Subject: [PATCH 1/2] fix(syscall): MAP_NORESERVE on aarch64 Linux via raw
 syscall
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

The existing raw-syscall path with MAP_NORESERVE was gated on
target_arch="x86_64" only. aarch64 Linux fell through to the libc::mmap
fallback that omits MAP_NORESERVE — fine for macOS (which has no equivalent
flag) but broken on Linux: with vm.overcommit_memory=0 (default on Asahi
Fedora and many other distros), the kernel rejects the multi-tens-of-GB
arena reservation and ensure_region aborts the process before any work
runs.

Reproduced on Apple Silicon M2 / Asahi Linux Fedora 42 (16 KiB pages, 16
GiB RAM, kernel 6.14.2). Patched build runs cleanly and is +3.4% faster
than standard-alloc on the leanMultisig 1550-sig XMSS aggregation
workload.

Adds a parallel imp module gated on (target_os=linux, target_arch=aarch64)
that mirrors the x86_64 raw-syscall path with the correct aarch64
syscall numbers (SYS_mmap=222, SYS_madvise=233) and ABI (svc 0, x8=nr,
x0..x5=args). The macOS path is unchanged.
---
 src/syscall.rs | 87 +++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 86 insertions(+), 1 deletion(-)

diff --git a/src/syscall.rs b/src/syscall.rs
index f676b2a..cae6ae5 100644
--- a/src/syscall.rs
+++ b/src/syscall.rs
@@ -92,7 +92,92 @@ mod imp {
     }
 }
 
-#[cfg(not(all(target_os = "linux", target_arch = "x86_64")))]
+#[cfg(all(target_os = "linux", target_arch = "aarch64"))]
+mod imp {
+    use std::ptr;
+
+    const SYS_MMAP: usize = 222;
+    const SYS_MADVISE: usize = 233;
+
+    const PROT_READ: usize = 1;
+    const PROT_WRITE: usize = 2;
+    const MAP_PRIVATE: usize = 0x02;
+    const MAP_ANONYMOUS: usize = 0x20;
+    const MAP_NORESERVE: usize = 0x4000;
+
+    pub const MADV_NOHUGEPAGE: usize = 15;
+
+    #[inline]
+    unsafe fn syscall6(
+        nr: usize,
+        a1: usize,
+        a2: usize,
+        a3: usize,
+        a4: usize,
+        a5: usize,
+        a6: usize,
+    ) -> isize {
+        let ret: isize;
+        unsafe {
+            std::arch::asm!(
+                "svc 0",
+                in("x8") nr,
+                inlateout("x0") a1 as isize => ret,
+                in("x1") a2,
+                in("x2") a3,
+                in("x3") a4,
+                in("x4") a5,
+                in("x5") a6,
+                options(nostack),
+            );
+        }
+        ret
+    }
+
+    #[inline]
+    unsafe fn syscall3(nr: usize, a1: usize, a2: usize, a3: usize) -> isize {
+        let ret: isize;
+        unsafe {
+            std::arch::asm!(
+                "svc 0",
+                in("x8") nr,
+                inlateout("x0") a1 as isize => ret,
+                in("x1") a2,
+                in("x2") a3,
+                options(nostack),
+            );
+        }
+        ret
+    }
+
+    #[inline]
+    pub unsafe fn mmap_anonymous(size: usize) -> *mut u8 {
+        let flags = MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE;
+        let ret = unsafe {
+            syscall6(
+                SYS_MMAP,
+                0,
+                size,
+                PROT_READ | PROT_WRITE,
+                flags,
+                usize::MAX,
+                0,
+            )
+        };
+        if ret < 0 {
+            ptr::null_mut()
+        } else {
+            ret as *mut u8
+        }
+    }
+
+    #[inline]
+    pub unsafe fn madvise(ptr: *mut u8, size: usize, advice: usize) {
+        unsafe { syscall3(SYS_MADVISE, ptr as usize, size, advice) };
+    }
+}
+
+#[cfg(not(all(target_os = "linux", any(target_arch = "x86_64", target_arch = "aarch64"))))]
 mod imp {
     use std::ptr;
 

From a9feef4d3e2a90c741ebe96cd519e20f1201de28 Mon Sep 17 00:00:00 2001
From: Barnadrot <kbarna.drot@gmail.com>
Date: Sun, 10 May 2026 12:39:43 -0400
Subject: [PATCH 2/2] chore: rustfmt for the new aarch64 cfg gate

---
 src/syscall.rs | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/syscall.rs b/src/syscall.rs
index cae6ae5..54f67d4 100644
--- a/src/syscall.rs
+++ b/src/syscall.rs
@@ -177,7 +177,10 @@ mod imp {
     }
 }
 
-#[cfg(not(all(target_os = "linux", any(target_arch = "x86_64", target_arch = "aarch64"))))]
+#[cfg(not(all(
+    target_os = "linux",
+    any(target_arch = "x86_64", target_arch = "aarch64")
+)))]
 mod imp {
     use std::ptr;