From 85f3e9f5cbde6e22965816a0d2328e208bc553f9 Mon Sep 17 00:00:00 2001
From: Matthew Flatt <mflatt@racket-lang.org>
Date: Thu, 20 Aug 2020 07:34:56 -0600
Subject: [PATCH] arm32: using ARMv6 memory fence

---
 racket/src/ChezScheme/c/version.h |  6 +++++-
 racket/src/ChezScheme/s/arm32.def |  2 ++
 racket/src/ChezScheme/s/arm32.ss  | 14 +++++++++-----
 3 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/racket/src/ChezScheme/c/version.h b/racket/src/ChezScheme/c/version.h
index 45fe7444d6..c9bdf2fd5d 100644
--- a/racket/src/ChezScheme/c/version.h
+++ b/racket/src/ChezScheme/c/version.h
@@ -470,7 +470,11 @@ typedef char tputsputcchar;
 #define USE_DEV_URANDOM_UUID
 
 #if defined(__arm64__) || defined(__arm32__)
-# define STORE_FENCE() __asm__ __volatile__ ("dmb ishst" : : : "memory")
+# if arm_isa_version == 6
+#  define STORE_FENCE() __asm__ __volatile__ ("mcr p15, 0, %0, c7, c10, 5" : : "r" (0) : "memory")
+# else
+#  define STORE_FENCE() __asm__ __volatile__ ("dmb ishst" : : : "memory")
+# endif
 #elif defined(__powerpc64__)
 # define STORE_FENCE() __asm__ __volatile__ ("lwsync" : : : "memory")
 #elif defined(__powerpc__) || defined(__POWERPC__)
diff --git a/racket/src/ChezScheme/s/arm32.def b/racket/src/ChezScheme/s/arm32.def
index 842477885c..1d757713b9 100644
--- a/racket/src/ChezScheme/s/arm32.def
+++ b/racket/src/ChezScheme/s/arm32.def
@@ -12,3 +12,5 @@
 
 (define-constant unaligned-floats #f)
 (define-constant unaligned-integers #t)
+
+(define-constant arm-isa-version 6)
diff --git a/racket/src/ChezScheme/s/arm32.ss b/racket/src/ChezScheme/s/arm32.ss
index a24d417268..c7ec4bf61c 100644
--- a/racket/src/ChezScheme/s/arm32.ss
+++ b/racket/src/ChezScheme/s/arm32.ss
@@ -2009,11 +2009,15 @@
   (define-who asm-fence
     (lambda (kind)
       (lambda (code*)
-        (case kind
-          [(store-store) (emit dmbishst code*)]
-          [(acquire) (emit dmbish code*)]
-          [(release) (emit dmbish code*)]
-          [else (sorry! who "unexpected kind ~s" kind)]))))
+        (constant-case arm-isa-version
+          [(6)
+           (emit mcr 'al #b1111 #b000 `(reg . ,%r0) #b0111 #b1010 #b101 code*)]
+          [(7)
+           (case kind
+             [(store-store) (emit dmbishst code*)]
+             [(acquire) (emit dmbish code*)]
+             [(release) (emit dmbish code*)]
+             [else (sorry! who "unexpected kind ~s" kind)])]))))
 
   (define asm-fp-relop
     (lambda (info)