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