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;
}
