On 5/22/20 2:14 PM, Leif Lindholm wrote:
On Fri, May 22, 2020 at 14:05:02 +0200, Ard Biesheuvel wrote:
On 5/22/20 1:41 PM, Leif Lindholm wrote:
On Fri, May 22, 2020 at 12:12:02 +0200, Ard Biesheuvel wrote:
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.biesheu...@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.

Hmm. I am just slightly concerned over referencing GCC 10.2 before GCC
10.2 is released.
Presumably, there will be no ill effects if that pragma is enabled also
on 10.2, we just won't need it? If so ...

No the pragma is only enabled on 10.2 and later. Older GCCs will choke on

Urgh, right. I guess I'm having a "can't read" day.

Still. That means that if the pragma gets pulled last second from
10.2, we now explicitly break builds for 10.2.
No matter how low the risk of that happening, this doesn't make me

Indeed. So assuming that we won't take the atomics patch for the stable tag, we already know it will be broken for all GCC 10 and up.

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