From 1b7ac7cab6a9abaf686fe7a7f4afea155c03d6a8 Mon Sep 17 00:00:00 2001 From: Greg Kurz Date: Mon, 7 Aug 2017 13:36:44 +0200 Subject: [PATCH] kvm: workaround build break on gcc-7.1.1 / fedora26 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Message-Id: <150210580404.1343.7325713896658799315.stgit@bahia.lan> Acked-by: Cornelia Huck Signed-off-by: Paolo Bonzini --- include/sysemu/kvm.h | 14 ++++---------- 1 file changed, 4 insertions(+), 10 deletions(-) diff --git a/include/sysemu/kvm.h b/include/sysemu/kvm.h index 91fc07ee9a..3a458f50e9 100644 --- a/include/sysemu/kvm.h +++ b/include/sysemu/kvm.h @@ -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); \ })