Re: [Minios-devel] [UNIKRAFT/LIBCXX PATCH] Fix crash due to atomics on bare-metal arm64

[Simon Kuenzer <simon.kuenzer@xxxxxxxxx>]

Thanks a lot. This patch looks fine.

Simon

Reviewed-by: Simon Kuenzer <simon.kuenzer@xxxxxxxxx>

On 28.01.20 13:55, Felipe Huici wrote:
> At the moment atomic operations are working on ARM64 for KVM; however,
> they are not working on baremetal on ARM64 (i.e., on the Raspberry Pi
> 3B+).  This can be most likely be solved by enabling the caches and
> setting up a compatible memory configuration.  In the meantime, these
> patches allow us to have functionally-equivalent non-atomic
> implementations of the gcc builtins working on baremetal on ARM64.
> Once the issue is fixed this workaround can be removed.
>
> Signed-off-by: Felipe Huici <felipe.huici@xxxxxxxxx>
> ---
>   patches/0004-Fix-arm-atomics-memory.patch | 28 +++++++++++++++++++++++
>   patches/0005-Fix-arm-atomics-header.patch | 19 +++++++++++++++
>   2 files changed, 47 insertions(+)
>   create mode 100644 patches/0004-Fix-arm-atomics-memory.patch
>   create mode 100644 patches/0005-Fix-arm-atomics-header.patch
>
> diff --git a/patches/0004-Fix-arm-atomics-memory.patch 
> b/patches/0004-Fix-arm-atomics-memory.patch
> new file mode 100644
> index 0000000..852805e
> --- /dev/null
> +++ b/patches/0004-Fix-arm-atomics-memory.patch
> @@ -0,0 +1,28 @@
> +--- a/include/memory   2020-01-28 13:27:53.843204834 +0100
> ++++ b/include/memory   2020-01-28 13:29:45.109925361 +0100
> +@@ -675,6 +675,7 @@
> + _LIBCPP_PUSH_MACROS
> + #include <__undef_macros>
> +
> ++#include <uk/arch/atomic.h>
> +
> + _LIBCPP_BEGIN_NAMESPACE_STD
> +
> +@@ -3458,7 +3459,7 @@
> + __libcpp_atomic_refcount_increment(_Tp& __t) _NOEXCEPT
> + {
> + #if defined(_LIBCPP_HAS_BUILTIN_ATOMIC_SUPPORT) && 
> !defined(_LIBCPP_HAS_NO_THREADS)
> +-    return __atomic_add_fetch(&__t, 1, __ATOMIC_RELAXED);
> ++    return ukarch_fetch_add(&__t, 1);
> + #else
> +     return __t += 1;
> + #endif
> +@@ -3469,7 +3470,7 @@
> + __libcpp_atomic_refcount_decrement(_Tp& __t) _NOEXCEPT
> + {
> + #if defined(_LIBCPP_HAS_BUILTIN_ATOMIC_SUPPORT) && 
> !defined(_LIBCPP_HAS_NO_THREADS)
> +-    return __atomic_add_fetch(&__t, -1, __ATOMIC_ACQ_REL);
> ++  return ukarch_dec(&__t);
> + #else
> +     return __t -= 1;
> + #endif
> diff --git a/patches/0005-Fix-arm-atomics-header.patch 
> b/patches/0005-Fix-arm-atomics-header.patch
> new file mode 100644
> index 0000000..75e27d2
> --- /dev/null
> +++ b/patches/0005-Fix-arm-atomics-header.patch
> @@ -0,0 +1,19 @@
> +--- a/src/include/atomic_support.h     2020-01-28 13:33:44.139173682 +0100
> ++++ b/src/include/atomic_support.h     2020-01-28 13:34:43.986484257 +0100
> +@@ -12,6 +12,7 @@
> +
> + #include "__config"
> + #include "memory" // for __libcpp_relaxed_load
> ++#include <uk/arch/atomic.h>
> +
> + #if defined(__clang__) && __has_builtin(__atomic_load_n)             \
> +                        && __has_builtin(__atomic_store_n)            \
> +@@ -80,7 +81,7 @@
> + _ValueType __libcpp_atomic_add(_ValueType* __val, _AddType __a,
> +                                int __order = _AO_Seq)
> + {
> +-    return __atomic_add_fetch(__val, __a, __order);
> ++  return ukarch_fetch_add(__val, __a);
> + }
> +
> + template <class _ValueType>
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