From 6fc11482063abc03f51f4834d35af099847d5cc3 Mon Sep 17 00:00:00 2001
From: Tarry Singh <tarry.singh@deepkapha.com>
Date: Mon, 10 Mar 2025 16:25:45 +0000
Subject: [PATCH] async/coro: make coroutines unwindable by zeroing the initial
 stack region, preventing random unwinding behavior and SIGSEGV during
 _Unwind_Backtrace.

---
 async/coro_base.zig | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/async/coro_base.zig b/async/coro_base.zig
index 7f77750..9cd6f1c 100644
--- a/async/coro_base.zig
+++ b/async/coro_base.zig
@@ -60,6 +60,13 @@ pub const Coro = packed struct {
             return Error.StackTooSmall;
         }
         const register_space = stack[stack.len - register_bytes ..];
+
+        // Zero out the register space so that the initial stack swap
+        // of new coroutines doesn't poison ebp.
+        //
+        // A better solution would be to prepare the initial stack so that the
+        // stack is valid up to the caller.
+        @memset(register_space, 0);
         const jump_ptr: *Func = @ptrCast(@alignCast(&register_space[arch_info.jump_idx * 8]));
         jump_ptr.* = func;
         return .{ .stack_pointer = register_space.ptr };