Upstream: https://github.com/ruby/ruby/pull/2995

From 9ce598b91e6ec8a146eec57c751d18dbebd2db60 Mon Sep 17 00:00:00 2001
From: Paul Jordan <paullj1@gmail.com>
Date: Wed, 1 Apr 2020 02:13:49 +0100
Subject: [PATCH 1/3] ucontext doesn't exist in a musl-libc env; use native
 assembly

---
 configure.ac | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/configure.ac b/configure.ac
index 5bc93800efd1..a054d163b316 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2353,8 +2353,8 @@ AS_CASE([$rb_cv_coroutine], [yes|''], [
         [*86-mingw32], [
             rb_cv_coroutine=win32
         ],
-        [armv7*-linux*], [
-            rb_cv_coroutine=ucontext
+        [arm*-linux*], [
+            rb_cv_coroutine=arm32
         ],
         [aarch64-linux*], [
             rb_cv_coroutine=arm64

From e2f04a9a9684ea3575546cc317dd16dba54ecbaf Mon Sep 17 00:00:00 2001
From: Paul Jordan <paullj1@gmail.com>
Date: Wed, 1 Apr 2020 02:15:20 +0100
Subject: [PATCH 2/3] Patch assembly so that it aligns properly

---
 coroutine/arm32/Context.S | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/coroutine/arm32/Context.S b/coroutine/arm32/Context.S
index 195364fb655f..b66db29622a4 100644
--- a/coroutine/arm32/Context.S
+++ b/coroutine/arm32/Context.S
@@ -5,9 +5,13 @@
 ##  Copyright, 2018, by Samuel Williams.
 ##
 
+.file "Context.S"
 .text
-
 .globl coroutine_transfer
+.align 2
+.type coroutine_transfer,%function
+.syntax unified
+
 coroutine_transfer:
 	# Save caller state (8 registers + return address)
 	push {r4-r11,lr}

From 360904b97e0f1012855cd150a59cc0074cfa7453 Mon Sep 17 00:00:00 2001
From: Paul Jordan <paullj1@gmail.com>
Date: Wed, 1 Apr 2020 02:18:23 +0100
Subject: [PATCH 3/3] Fix helper to not assume glibc

---
 test/fiddle/helper.rb | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/test/fiddle/helper.rb b/test/fiddle/helper.rb
index 348131e4480f..f5c7bd2ca6c7 100644
--- a/test/fiddle/helper.rb
+++ b/test/fiddle/helper.rb
@@ -32,7 +32,11 @@
       # libc.so and libm.so are installed to /lib/arm-linux-gnu*.
       # It's not installed to /lib32.
       dirs = Dir.glob('/lib/arm-linux-gnu*')
-      libdir = dirs[0] if dirs && File.directory?(dirs[0])
+      if dirs.length > 0
+        libdir = dirs[0] if dirs && File.directory?(dirs[0])
+      else # handle alpine environment
+        libdir = '/lib' if File.directory? '/lib'
+      end
     else
       libdir = '/lib32' if File.directory? '/lib32'
     end
@@ -40,8 +44,17 @@
     # 64-bit ruby
     libdir = '/lib64' if File.directory? '/lib64'
   end
-  libc_so = File.join(libdir, "libc.so.6")
-  libm_so = File.join(libdir, "libm.so.6")
+
+  # Handle musl libc
+  libc = Dir.glob(File.join(libdir, "libc.musl*.so*"))
+  if libc && libc.length > 0
+    libc_so = libc[0]
+    libm_so = libc[0]
+  else
+    # glibc
+    libc_so = File.join(libdir, "libc.so.6")
+    libm_so = File.join(libdir, "libm.so.6")
+  end
 when /mingw/, /mswin/
   require "rbconfig"
   crtname = RbConfig::CONFIG["RUBY_SO_NAME"][/msvc\w+/] || 'ucrtbase'