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[PULL,11/15] hw/i386: fix short-circuit logic with non-optimizing builds

Message ID 74b665da374aa1462fe3067415ffe167621fccc7.1701450838.git.mst@redhat.com (mailing list archive)
State New, archived
Headers show
Series [PULL,01/15] osdep: add getloadavg | expand

Commit Message

Michael S. Tsirkin Dec. 1, 2023, 5:15 p.m. UTC 
From: Daniel Hoffman <dhoff749@gmail.com>

`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

Signed-off-by: Daniel Hoffman <dhoff749@gmail.com>
Message-Id: <20231119203116.3027230-1-dhoff749@gmail.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 hw/i386/x86.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)
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Patch

diff --git a/hw/i386/x86.c b/hw/i386/x86.c
index b3d054889b..2b6291ad8d 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;
     }