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[packages/trusty/cirros-testvm.git] / cirros-testvm / src-cirros / buildroot-2015.05 / package / erlang / 0002-erts-ethread-instruct-libatomic_ops-we-do-require-CA.patch

diff --git a/cirros-testvm/src-cirros/buildroot-2015.05/package/erlang/0002-erts-ethread-instruct-libatomic_ops-we-do-require-CA.patch b/cirros-testvm/src-cirros/buildroot-2015.05/package/erlang/0002-erts-ethread-instruct-libatomic_ops-we-do-require-CA.patch
new file mode 100644 (file)
index 0000000..8e40143
--- /dev/null
+++ b/cirros-testvm/src-cirros/buildroot-2015.05/package/erlang/0002-erts-ethread-instruct-libatomic_ops-we-do-require-CA.patch
@@ -0,0 +1,70 @@
+From 439fa2eae78a8900bda120072335be19d626498c Mon Sep 17 00:00:00 2001
+From: "Yann E. MORIN" <yann.morin.1998@free.fr>
+Date: Sun, 28 Dec 2014 23:39:40 +0100
+Subject: [PATCH] erts/ethread: instruct libatomic_ops we do require CAS
+
+We do require compare-and-swap (CAS), so we must instruct libatomic_ops
+to provide it, even if the architecture does not have instructions for
+it.
+
+For example, on ARM, LDREX is required for fast CAS. But LDREX is only
+available on ARMv6, so by default libatomic_ops will not have CAS for
+anything below, like ARMv5. But ARMv5 is always UP, so using an
+emulated CAS (that is signal-asyn-safe) is still possible (albeit much
+slower).
+
+Tell libatomic_ops to provide CAS, even if the hardware is not capable
+of it, by using emulated CAS, as per libatomic_ops dosc:
+    https://github.com/ivmai/libatomic_ops/blob/master/doc/README.txt#L28
+
+    If this is included after defining AO_REQUIRE_CAS, then the package
+    will make an attempt to emulate compare-and-swap in a way that (at
+    least on Linux) should still be async-signal-safe.
+
+Thanks go to Thomas for all this insight! :-)
+Thanks go to Frank for reporting the issue! :-)
+
+Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
+Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
+Cc: Frank Hunleth <fhunleth@troodon-software.com>
+---
+ erts/include/internal/libatomic_ops/ethread.h | 1 +
+ 1 file changed, 1 insertion(+)
+
+diff --git a/erts/include/internal/libatomic_ops/ethread.h b/erts/include/internal/libatomic_ops/ethread.h
+index d65ee19..71d3598 100644
+--- a/erts/include/internal/libatomic_ops/ethread.h
++++ b/erts/include/internal/libatomic_ops/ethread.h
+@@ -35,6 +35,7 @@
+ 
+ #define ETHR_NATIVE_IMPL__ "libatomic_ops"
+ 
++#define AO_REQUIRE_CAS
+ #include "atomic_ops.h"
+ #include "ethr_membar.h"
+ #include "ethr_atomic.h"
+diff --git a/erts/aclocal.m4 b/erts/aclocal.m4
+index d65ee19..71d3598 100644
+--- a/erts/aclocal.m4
++++ b/erts/aclocal.m4
+@@ -1414,7 +1414,8 @@
+                   fi;;
+           esac
+           ethr_have_libatomic_ops=no
+-          AC_TRY_LINK([#include "atomic_ops.h"],
++          AC_TRY_LINK([#define AO_REQUIRE_CAS
++                    #include "atomic_ops.h"],
+                       [
+                           volatile AO_t x;
+                           AO_t y;
+@@ -1455,6 +1455,7 @@
+               AC_CHECK_SIZEOF(AO_t, ,
+                               [
+                                   #include <stdio.h>
++                                  #define AO_REQUIRE_CAS
+                                   #include "atomic_ops.h"
+                               ])
+               AC_DEFINE_UNQUOTED(ETHR_SIZEOF_AO_T, $ac_cv_sizeof_AO_t, [Define to the size of AO_t if libatomic_ops is used])
+-- 
+1.9.1
+