[edk2-devel] [PATCH] MdePkg/Include: AARCH64: disable outline atomics on GCC 10.2+

[Ard Biesheuvel]

GCC 10 enabled a feature by default that was introduced in GCC 9,
which results in atomic operations to be emitted as function calls
to intrinsics provided by a runtime library.

Atomics are hardly used in EDK2, which runs on a single CPU anyway,
and any benefit that would result from reusing library code that
implements these operations is defeated by the fact that every EDK2
module will need to have its own copy anyway.

So let's disable this feature on GCC versions that support the
pragma to do so (GCC 10.2 and up)

Link: https://bugzilla.tianocore.org/show_bug.cgi?id=2723
Signed-off-by: Ard Biesheuvel <ard.biesheuvel at arm.com>
---
The GCC support for this pragma has already been pulled into the 10.2
release branch. I think we should consider adding this to the stable
tag, so that the issue can easily be resolved by upgrading the compiler.
Whether we add the intrinsics too is a separate matter, but we can
revisit that later.

 MdePkg/Include/AArch64/ProcessorBind.h | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/MdePkg/Include/AArch64/ProcessorBind.h b/MdePkg/Include/AArch64/ProcessorBind.h
index 896bf273ac7a..a3ca8f09e51c 100644
--- a/MdePkg/Include/AArch64/ProcessorBind.h
+++ b/MdePkg/Include/AArch64/ProcessorBind.h
@@ -24,6 +24,17 @@
 #pragma pack()
 #endif
 
+#if defined(__GNUC__) && !defined(__clang__)
+
+//
+// Disable GCC outline atomics
+// Link: https://bugzilla.tianocore.org/show_bug.cgi?id=2723
+//
+#if __GNUC__ > 10 || (__GNUC__ == 10 && __GNUC_MINOR__ >= 2)
+#pragma GCC target "no-outline-atomics"
+#endif
+#endif
+
 #if defined(_MSC_EXTENSIONS)
 
 //
-- 
2.17.1


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