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kvm: workaround build break on gcc-7.1.1 / fedora26

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Building QEMU on fedora26 with the latest gcc package fails:

  CC      ppc64-softmmu/target/ppc/kvm.o
In file included from include/sysemu/hw_accel.h:16:0,
                 from target/ppc/kvm.c:31:
target/ppc/kvm.c: In function ‘kvmppc_booke_watchdog_enable’:
include/sysemu/kvm.h:449:35: error: ‘args_tmp[i]’ may be used uninitialized
 in this function [-Werror=maybe-uninitialized]
             cap.args[i] = args_tmp[i];                               \
                                   ^
target/ppc/kvm.c: In function ‘kvmppc_set_papr’:
include/sysemu/kvm.h:449:35: error: ‘args_tmp[i]’ may be used uninitialized
 in this function [-Werror=maybe-uninitialized]
cc1: all warnings being treated as errors

$ rpm -q gcc
gcc-7.1.1-3.fc26.ppc64le

The compiler should obviously optimize this code away when no extra
agument is passed to kvm_vm_enable_cap() and kvm_vcpu_enable_cap(),
but it doesn't. This bug should be fixed one day in gcc, but we can
also change our code pattern so that we don't hit the issue anymore.
We workaround this, by using memcpy() instead of open-coding the copy.

Signed-off-by: Greg Kurz <groug@kaod.org>
Message-Id: <150210580404.1343.7325713896658799315.stgit@bahia.lan>
Acked-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Greg Kurz 2017-08-07 13:36:44 +02:00 committed by Paolo Bonzini
parent 2a96a552f9
commit 1b7ac7cab6
1 changed files with 4 additions and 10 deletions
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14
include/sysemu/kvm.h
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@ -428,11 +428,8 @@ int kvm_vm_check_extension(KVMState *s, unsigned int extension);
.flags = cap_flags, \
}; \
uint64_t args_tmp[] = { __VA_ARGS__ }; \
int i; \
for (i = 0; i < (int)ARRAY_SIZE(args_tmp) && \
i < ARRAY_SIZE(cap.args); i++) { \
cap.args[i] = args_tmp[i]; \
} \
size_t n = MIN(ARRAY_SIZE(args_tmp), ARRAY_SIZE(cap.args)); \
memcpy(cap.args, args_tmp, n * sizeof(cap.args[0])); \
kvm_vm_ioctl(s, KVM_ENABLE_CAP, &cap); \
})
@ -443,11 +440,8 @@ int kvm_vm_check_extension(KVMState *s, unsigned int extension);
.flags = cap_flags, \
}; \
uint64_t args_tmp[] = { __VA_ARGS__ }; \
int i; \
for (i = 0; i < (int)ARRAY_SIZE(args_tmp) && \
i < ARRAY_SIZE(cap.args); i++) { \
cap.args[i] = args_tmp[i]; \
} \
size_t n = MIN(ARRAY_SIZE(args_tmp), ARRAY_SIZE(cap.args)); \
memcpy(cap.args, args_tmp, n * sizeof(cap.args[0])); \
kvm_vcpu_ioctl(cpu, KVM_ENABLE_CAP, &cap); \
})