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makefiles: Disable -Watomic-alignment on LLVM

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`-Watomic-alignment` warns when C11 atomics have to be implemented via a to one
of the functions in `core/atomic_c11.c`. Unlike to the context of Desktop or
Server class machines, the performance penalty of this calls is insignificant
(and not existing with LTO). So this is not an issue in our context.

On the other hand: Keeping `-Watomic-alignment` prevents building applications
using C11 atomics on all platforms the atomic operations are not implemented
without calls to `core/atomic_c11.c` (due to `-Werror`), reducing portability.

So not only does the warning is not useful in our context, it actually prevents
portable use of C11 atomics. It is the most sensible thing to just disable it.
This commit is contained in:
Marian Buschsieweke 2019-10-09 10:15:47 +02:00
parent 7794c29650
commit 716fc76f13
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1 changed files with 12 additions and 0 deletions
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12
makefiles/toolchain/llvm.inc.mk
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@ -72,6 +72,18 @@ ifneq (,$(TARGET_ARCH))
CXXINCLUDES += $(GCC_CXX_INCLUDES)
endif
# For bare metal targets the performance penalty of atomic operations being
# implemented with library calls is totally insignificant. In case LTO is
# is enabled, the overhead compared to manually disabling interrupts is fully
# optimized out (unless atomic operations could be grouped together to a single
# critical section). So there is - in our use case - no value in having the
# warning
CFLAGS += -Wno-atomic-alignment
# For compatibility with older clang versions we also disable warnings on
# unsupported warning flags:
CFLAGS += -Wno-unknown-warning-option
OPTIONAL_CFLAGS_BLACKLIST += -fno-delete-null-pointer-checks
OPTIONAL_CFLAGS_BLACKLIST += -Wformat-overflow
OPTIONAL_CFLAGS_BLACKLIST += -Wformat-truncation