[Qemu-devel] [PATCH] target/i386/kvm.c: Don't mark cpuid_data as QEMU_PACKED

[Peter Maydell <peter.maydell@linaro.org>]

clang complains about taking the address of a packed
member of a struct:

target/i386/kvm.c:1245:27: warning: taking address of packed member 'cpuid' of class or structure '' may result in an unaligned pointer value [-Waddress-of-packed-member]
    c = cpuid_find_entry(&cpuid_data.cpuid, 1, 0);
                          ^~~~~~~~~~~~~~~~
target/i386/kvm.c:1297:31: warning: taking address of packed member 'cpuid' of class or structure '' may result in an unaligned pointer value [-Waddress-of-packed-member]
        c = cpuid_find_entry(&cpuid_data.cpuid, kvm_base, 0);
                              ^~~~~~~~~~~~~~~~

The kernel's definitions of struct kvm_cpuid2 and struct
kvm_cpuid_entry2 are carefully set up with padding fields
so that there is no between-struct padding anyway, so
the QEMU_PACKED annotation is unnecessary and might result
in the compiler generating worse code. Drop it, and instead
assert at build time that there is no stray padding.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 target/i386/kvm.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/target/i386/kvm.c b/target/i386/kvm.c
index b2401d13ea7..739cf8c8ea1 100644
--- a/target/i386/kvm.c
+++ b/target/i386/kvm.c
@@ -864,7 +864,15 @@ int kvm_arch_init_vcpu(CPUState *cs)
     struct {
         struct kvm_cpuid2 cpuid;
         struct kvm_cpuid_entry2 entries[KVM_MAX_CPUID_ENTRIES];
-    } QEMU_PACKED cpuid_data;
+    } cpuid_data;
+    /*
+     * The kernel defines these structs with padding fields so there
+     * should be no extra padding in our cpuid_data struct.
+     */
+    QEMU_BUILD_BUG_ON(sizeof(cpuid_data) !=
+                      sizeof(struct kvm_cpuid2) +
+                      sizeof(struct kvm_cpuid_entry2) * KVM_MAX_CPUID_ENTRIES);
+
     X86CPU *cpu = X86_CPU(cs);
     CPUX86State *env = &cpu->env;
     uint32_t limit, i, j, cpuid_i;
-- 
2.19.2