(Cc'ing Eric)
On 20/11/23 10:28, Michael S. Tsirkin wrote:
On Sun, Nov 19, 2023 at 07:34:58PM -0600, Dan Hoffman wrote:
As far as I can tell, yes. Any optimization level above O0 does not have this
issue (on this version of Clang, at least)
Aha, this is with -O0. That makes sense.
But then, why the other cases aren't problematic?
$ git grep -E ' (&&|\|\|) !?kvm_enabled'
hw/arm/boot.c:1228: assert(!(info->secure_board_setup && kvm_enabled()));
hw/i386/microvm.c:270: (mms->rtc == ON_OFF_AUTO_AUTO &&
!kvm_enabled())) {
hw/i386/x86.c:135: if (x86ms->apic_id_limit > 255 && kvm_enabled() &&
hw/mips/cps.c:62: return is_mt && !kvm_enabled();
system/physmem.c:760: assert(asidx == 0 || !kvm_enabled());
target/arm/cpu64.c:288: if (value && kvm_enabled() &&
!kvm_arm_sve_supported()) {
target/i386/cpu.c:7264: if (requested_lbr_fmt && kvm_enabled()) {
target/ppc/kvm.c:345: if (!cpu->hash64_opts || !kvm_enabled()) {
target/s390x/cpu_models.c:574: if (xcc->kvm_required && !kvm_enabled()) {
target/s390x/cpu_models_sysemu.c:124: if
(S390_CPU_CLASS(oc)->kvm_required && !kvm_enabled()) {
We have:
;;
--enable-debug)
# Enable debugging options that aren't excessively noisy
meson_option_parse --enable-debug-tcg ""
meson_option_parse --enable-debug-graph-lock ""
meson_option_parse --enable-debug-mutex ""
meson_option_add -Doptimization=0
default_cflags='-O0 -g'
On Sun, Nov 19, 2023 at 4:54 PM Philippe Mathieu-Daudé <phi...@linaro.org>
wrote:
Hi,
On 19/11/23 21:31, Daniel Hoffman wrote:
> `kvm_enabled()` is compiled down to `0` and short-circuit logic is
> used to remove references to undefined symbols at the compile stage.
> Some build configurations with some compilers don't attempt to
> simplify this logic down in some cases (the pattern appears to be
> that the literal false must be the first term) and this was causing
> some builds to emit references to undefined symbols.
>
> An example of such a configuration is clang 16.0.6 with the following
> configure: ./configure --enable-debug --without-default-features
> --target-list=x86_64-softmmu --enable-tcg-interpreter
Is the '--enable-debug' option triggering this?
I'm surprised the order of conditions matters for code elision...
> Signed-off-by: Daniel Hoffman <dhoff...@gmail.com>
> ---
> hw/i386/x86.c | 15 ++++++++++++---
> 1 file changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/hw/i386/x86.c b/hw/i386/x86.c
> index b3d054889bb..2b6291ad8d5 100644
> --- a/hw/i386/x86.c
> +++ b/hw/i386/x86.c
> @@ -131,8 +131,12 @@ void x86_cpus_init(X86MachineState *x86ms, int
default_cpu_version)
> /*
> * Can we support APIC ID 255 or higher? With KVM, that requires
> * both in-kernel lapic and X2APIC userspace API.
> + *
> + * kvm_enabled() must go first to ensure that kvm_* references are
> + * not emitted for the linker to consume (kvm_enabled() is
> + * a literal `0` in configurations where kvm_* aren't defined)
> */
> - if (x86ms->apic_id_limit > 255 && kvm_enabled() &&
> + if (kvm_enabled() && x86ms->apic_id_limit > 255 &&
> (!kvm_irqchip_in_kernel() || !kvm_enable_x2apic())) {
> error_report("current -smp configuration requires kernel "
> "irqchip and X2APIC API support.");
> @@ -418,8 +422,13 @@ void x86_cpu_pre_plug(HotplugHandler *hotplug_dev,
> }
> cpu->thread_id = topo_ids.smt_id;
>
> - if (hyperv_feat_enabled(cpu, HYPERV_FEAT_VPINDEX) &&
> - kvm_enabled() && !kvm_hv_vpindex_settable()) {
> + /*
> + * kvm_enabled() must go first to ensure that kvm_* references are
> + * not emitted for the linker to consume (kvm_enabled() is
> + * a literal `0` in configurations where kvm_* aren't defined)
> + */
> + if (kvm_enabled() && hyperv_feat_enabled(cpu, HYPERV_FEAT_VPINDEX) &
&
> + !kvm_hv_vpindex_settable()) {
> error_setg(errp, "kernel doesn't allow setting HyperV
VP_INDEX");
> return;
> }
