为什么 git show 查看 merge tag 的 commit 时会有 diff 的输出？

例如 linux 内核的这个 commit

git show 38904911e86495d4690f8d805720b90e65426c71 的输出如下:

commit 38904911e86495d4690f8d805720b90e65426c71 Merge: 6f34f8c3d617 c15e0ae42c8e Author: Linus Torvalds <[email protected]> Date: Sat Apr 2 12:09:02 2022 -0700 Merge tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm Pull kvm fixes from Paolo Bonzini: - Only do MSR filtering for MSRs accessed by rdmsr/wrmsr - Documentation improvements - Prevent module exit until all VMs are freed - PMU Virtualization fixes - Fix for kvm_irq_delivery_to_apic_fast() NULL-pointer dereferences - Other miscellaneous bugfixes * tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm: (42 commits) KVM: x86: fix sending PV IPI KVM: x86/mmu: do compare-and-exchange of gPTE via the user address KVM: x86: Remove redundant vm_entry_controls_clearbit() call KVM: x86: cleanup enter_rmode() KVM: x86: SVM: fix tsc scaling when the host doesn't support it kvm: x86: SVM: remove unused defines KVM: x86: SVM: move tsc ratio definitions to svm.h KVM: x86: SVM: fix avic spec based definitions again KVM: MIPS: remove reference to trap&emulate virtualization KVM: x86: document limitations of MSR filtering KVM: x86: Only do MSR filtering when access MSR by rdmsr/wrmsr KVM: x86/emulator: Emulate RDPID only if it is enabled in guest KVM: x86/pmu: Fix and isolate TSX-specific performance event logic KVM: x86: mmu: trace kvm_mmu_set_spte after the new SPTE was set KVM: x86/svm: Clear reserved bits written to PerfEvtSeln MSRs KVM: x86: Trace all APICv inhibit changes and capture overall status KVM: x86: Add wrappers for setting/clearing APICv inhibits KVM: x86: Make APICv inhibit reasons an enum and cleanup naming KVM: X86: Handle implicit supervisor access with SMAP KVM: X86: Rename variable smap to not_smap in permission_fault() ... diff --cc arch/x86/include/asm/kvm_host.h index 4138939532c6,93a2671a57cf..d23e80a56eb8 --- aarch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@@ -512,9 -513,10 +514,10 @@@ struct kvm_pmu u64 global_ctrl_mask; u64 global_ovf_ctrl_mask; u64 reserved_bits; + u64 raw_event_mask; u8 version; struct kvm_pmc gp_counters[INTEL_PMC_MAX_GENERIC]; - struct kvm_pmc fixed_counters[INTEL_PMC_MAX_FIXED]; + struct kvm_pmc fixed_counters[KVM_PMC_MAX_FIXED]; struct irq_work irq_work; DECLARE_BITMAP(reprogram_pmi, X86_PMC_IDX_MAX); DECLARE_BITMAP(all_valid_pmc_idx, X86_PMC_IDX_MAX); 

我认为这里不应该有 diff 的输出，而且这个 diff 的输出我完全看不出有什么意义。