From 52d33b6ae41e86e81423d0dcb3e072de7be53789 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Alex=20R=C3=B8nne=20Petersen?= <alex@alexrp.com>
Date: Thu, 4 Jun 2026 00:36:25 +0200
Subject: [PATCH] std.os.linux.sparc64: work around kernel bug with uncommitted
 stack in clone()

https://sourceware.org/bugzilla/show_bug.cgi?id=31394
---
 lib/std/os/linux/sparc64.zig | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/lib/std/os/linux/sparc64.zig b/lib/std/os/linux/sparc64.zig
index 09926745dd2bd9299eacfe2bc61fe9527268229c..ad7915266facac5e722b7ec5722f111a97f80414 100644
--- a/lib/std/os/linux/sparc64.zig
+++ b/lib/std/os/linux/sparc64.zig
@@ -196,17 +196,28 @@ pub fn clone() callconv(.naked) u64 {
     //         g1         o0,    o1,    o2,   o3,  o4
     asm volatile (
         \\ save %%sp, -192, %%sp
+        \\
+        \\ // clone() on SPARC can fail with EFAULT if %%sp points to uncommitted memory, so flush
+        \\ // all register windows up to this point to ensure that the kernel has enough committed
+        \\ // memory for its stack frame.
+        \\ save %%sp, -192, %%sp
+        \\ flushw
+        \\ restore
+        \\
         \\ # Save the func pointer and the arg pointer
         \\ mov %%i0, %%g2
         \\ mov %%i3, %%g3
+        \\
         \\ # Shuffle the arguments
         \\ mov 217, %%g1 // SYS_clone
         \\ mov %%i2, %%o0
+        \\
         \\ # Add some extra space for the initial frame
-        \\ sub %%i1, 176 + 2047, %%o1
+        \\ sub %%i1, 192 + 2047, %%o1
+        \\
         \\ mov %%i4, %%o2
         \\ mov %%i5, %%o3
-        \\ ldx [%%fp + 0x8af], %%o4
+        \\ ldx [%%fp + 176 + 2047], %%o4
         \\ t 0x6d
         \\ bcs,pn %%xcc, 1f
         \\  nop
@@ -214,15 +225,18 @@ pub fn clone() callconv(.naked) u64 {
         \\ # process is the child (=1) or the parent (=0).
         \\ brnz %%o1, 2f
         \\  nop
+        \\
         \\ # Parent process, return the child pid
         \\ mov %%o0, %%i0
         \\ ret
         \\  restore
+        \\
         \\1:
         \\ # The syscall failed
         \\ sub %%g0, %%o0, %%i0
         \\ ret
         \\  restore
+        \\
         \\2:
         \\ # Child process
     );
-- 
2.54.0