From: Richard Henderson <richard.henderson@linaro.org>
To: qemu-devel@nongnu.org
Cc: peter.maydell@linaro.org, pbonzini@redhat.com, crobinso@redhat.com
Subject: [PATCH 3/3] configure: Conditionally disable clang-12 -Watomic-alignment
Date: Mon, 12 Jul 2021 08:59:18 -0700 [thread overview]
Message-ID: <20210712155918.1422519-4-richard.henderson@linaro.org> (raw)
In-Reply-To: <20210712155918.1422519-1-richard.henderson@linaro.org>
The i386 abi does not align uint64_t (or double) in structures to 8
bytes, only to 4 bytes. Furthermore, the hardware does not require
8 byte alignent for cmpxchg8b, so the warning is confusing and useless.
Retain the warning for hosts (notably x86_64) where the ABI is sane,
and one has to do something extraordinary to remove alignment.
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
configure | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
diff --git a/configure b/configure
index 95e0a08938..163b4edee2 100755
--- a/configure
+++ b/configure
@@ -3927,6 +3927,22 @@ if compile_prog "" "" ; then
atomic64=yes
fi
+# Test for clang atomic misalignment warning vs ABI structure misalignment.
+# E.g. i386 only aligns structures to 4 bytes by default.
+if test "$atomic64" = "yes" ; then
+cat > $TMPC << EOF
+#include <stdint.h>
+struct X { uint64_t x; };
+uint64_t foo(struct X *p) { return __atomic_exchange_n(&p->x, 0, 0); }
+EOF
+ if ! compile_prog "-Werror" "" ; then
+ if cc_has_warning_flag "-Wno-atomic-alignment" ; then
+ glib_cflags="-Wno-atomic-alignment $glib_cflags"
+ CONFIGURE_CFLAGS="$CONFIGURE_CFLAGS -Wno-atomic-alignment"
+ fi
+ fi
+fi
+
#########################################
# See if --dynamic-list is supported by the linker
ld_dynamic_list="no"
--
2.25.1
next prev parent reply other threads:[~2021-07-12 16:02 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-12 15:59 [PATCH 0/3] Atomic cleanup + clang-12 build fix Richard Henderson
2021-07-12 15:59 ` [PATCH 1/3] qemu/atomic: Remove pre-C11 atomic fallbacks Richard Henderson
2021-07-12 15:59 ` [PATCH 2/3] qemu/atomic: Use macros for CONFIG_ATOMIC64 Richard Henderson
2021-07-12 16:29 ` Philippe Mathieu-Daudé
2021-07-12 15:59 ` Richard Henderson [this message]
2021-07-12 21:30 ` [PATCH 0/3] Atomic cleanup + clang-12 build fix Cole Robinson
2021-07-13 0:37 ` Richard Henderson
2021-07-13 14:43 ` Richard Henderson
2021-07-13 15:18 ` Cole Robinson
2021-07-13 16:56 ` Richard Henderson
2021-07-15 15:11 ` Cole Robinson
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