From e8fda704de72dead9a6f0aa00b8dd1451b5bd74d Mon Sep 17 00:00:00 2001
From: Juan Wajnerman <jwajnerman@manas.com.ar>
Date: Wed, 6 May 2020 16:42:48 -0300
Subject: [PATCH] Force linking of `pthread_once` when compiling static
 binaries in musl

---
 src/crystal/system/unix/pthread.cr | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/src/crystal/system/unix/pthread.cr b/src/crystal/system/unix/pthread.cr
index 67e7979cbd70..005d71cfc17f 100644
--- a/src/crystal/system/unix/pthread.cr
+++ b/src/crystal/system/unix/pthread.cr
@@ -178,3 +178,19 @@ class Thread
     @th
   end
 end
+
+# In musl (alpine) the calls to unwind API segfaults
+# when the binary is statically linked. This is because
+# some symbols like `pthread_once` are defined as "weak"
+# and, for some reason, not linked into the final binary.
+# Adding an explicit reference to the symbol ensures it's
+# included in the statically linked binary.
+{% if flag?(:musl) && flag?(:static) %}
+  lib LibC
+    fun pthread_once(Void*, Void*)
+  end
+
+  fun __crystal_static_musl_workaround
+    LibC.pthread_once(nil, nil)
+  end
+{% end %}