Add ability to debug additional registers via gdb

src/hyperlight_host/src/hypervisor/gdb/hyperv_debug.rs

@@ -211,6 +211,18 @@ impl GuestDebug for HypervDebug {
         regs.rip = vcpu_regs.rip;
         regs.rflags = vcpu_regs.rflags;
 
+        // Fetch XMM from WHVP
+        if let Ok(fpu) = vcpu_fd.get_fpu() {
+            regs.xmm = [
+                fpu.xmm0, fpu.xmm1, fpu.xmm2, fpu.xmm3, fpu.xmm4, fpu.xmm5, fpu.xmm6, fpu.xmm7,
+                fpu.xmm8, fpu.xmm9, fpu.xmm10, fpu.xmm11, fpu.xmm12, fpu.xmm13, fpu.xmm14,
+                fpu.xmm15,
+            ];
+            regs.mxcsr = fpu.mxcsr;
+        } else {
+            log::warn!("Failed to read FPU/XMM via WHVP for debug registers");
+        }
+
         Ok(())
     }
 

src/hyperlight_host/src/hypervisor/gdb/kvm_debug.rs

@@ -16,6 +16,7 @@ limitations under the License.
 
 use std::collections::HashMap;
 
+use gdbstub_arch::msp430::reg;
 use kvm_bindings::{
     KVM_GUESTDBG_ENABLE, KVM_GUESTDBG_SINGLESTEP, KVM_GUESTDBG_USE_HW_BP, KVM_GUESTDBG_USE_SW_BP,
     kvm_debug_exit_arch, kvm_guest_debug, kvm_regs,
@@ -193,6 +194,31 @@ impl GuestDebug for KvmDebug {
         regs.rip = vcpu_regs.rip;
         regs.rflags = vcpu_regs.rflags;
 
+         // Read XMM registers from FPU state
+        // note kvm get_fpu doesn't actually set or read the mxcsr value
+        // https://elixir.bootlin.com/linux/v6.16/source/arch/x86/kvm/x86.c#L12229
+        match vcpu_fd.get_fpu() {
+            Ok(fpu) => {
+                // Convert KVM XMM registers ([u8; 16] x 16) to [u128; 16]
+                regs.xmm = fpu.xmm.map(u128::from_le_bytes);
+            },
+            Err(e) => {
+                log::warn!("Failed to read FPU state for XMM registers: {:?}", e);
+            }
+        }
+
+        // Read MXCSR from XSAVE (MXCSR is at byte offset 24 -> u32 index 6)
+        // Todo maybe I could use xsave to read the registers too instead of a separate call to get_fpu
+        match vcpu_fd.get_xsave() {
+            Ok(xsave) => {
+                regs.mxcsr = xsave.region[6];
+
+            }
+            Err(e) => {
+                log::warn!("Failed to read XSAVE for MXCSR: {:?}", e);
+            }
+        }
+
         Ok(())
     }
 

src/hyperlight_host/src/hypervisor/gdb/mod.rs

@@ -108,6 +108,8 @@ pub(crate) struct X86_64Regs {
     pub(crate) r15: u64,
     pub(crate) rip: u64,
     pub(crate) rflags: u64,
+    pub(crate) xmm: [u128; 16],
+    pub(crate) mxcsr: u32,
 }
 
 /// Defines the possible reasons for which a vCPU can be stopped when debugging

src/hyperlight_host/src/hypervisor/gdb/mshv_debug.rs

@@ -220,6 +220,18 @@ impl GuestDebug for MshvDebug {
         regs.rip = vcpu_regs.rip;
         regs.rflags = vcpu_regs.rflags;
 
+        // Try to read XMM from the FPU state
+        match vcpu_fd.get_fpu() {
+            Ok(fpu) => {
+                // MSHV exposes XMM as [[u8; 16]; 16]. Convert to [u128; 16]
+                regs.xmm = fpu.xmm.map(u128::from_le_bytes);
+                regs.mxcsr = fpu.mxcsr;
+            }
+            Err(e) => {
+                log::warn!("Failed to read FPU state for XMM registers (MSHV): {:?}", e);
+            }
+        }
+
         Ok(())
     }
 
@@ -258,6 +270,8 @@ impl GuestDebug for MshvDebug {
 
             rip: regs.rip,
             rflags: regs.rflags,
+
+
         };
 
         vcpu_fd

src/hyperlight_host/src/hypervisor/gdb/x86_64_target.rs

@@ -227,6 +227,8 @@ impl SingleThreadBase for HyperlightSandboxTarget {
                 regs.regs[15] = read_regs.r15;
                 regs.rip = read_regs.rip;
                 regs.eflags = read_regs.rflags as u32;
+                regs.xmm = read_regs.xmm;
+                regs.mxcsr = read_regs.mxcsr;
 
                 Ok(())
             }
@@ -267,6 +269,8 @@ impl SingleThreadBase for HyperlightSandboxTarget {
             r15: regs.regs[15],
             rip: regs.rip,
             rflags: u64::from(regs.eflags),
+            xmm: regs.xmm,
+            mxcsr: regs.mxcsr,
         };
 
         match self.send_command(DebugMsg::WriteRegisters(regs))? {

src/hyperlight_host/src/hypervisor/kvm.rs

@@ -591,6 +591,9 @@ impl Hypervisor for KVMDriver {
             mxcsr: MXCSR_DEFAULT,
             ..Default::default() // zero out the rest
         };
+
+        // note kvm set_fpu doesn't actually set or read the mxcsr value
+        // https://elixir.bootlin.com/linux/v6.16/source/arch/x86/kvm/x86.c#L12229
         self.vcpu_fd.set_fpu(&fpu)?;
 
         // run

src/hyperlight_host/src/hypervisor/windows_hypervisor_platform.rs

@@ -696,6 +696,124 @@ impl VMProcessor {
         Ok(())
     }
 
+    pub(super) fn get_fpu(&self) -> Result<WHvFPURegisters> {
+        use windows::Win32::System::Hypervisor::*;
+
+        const LEN: usize = 26;
+        let names: [WHV_REGISTER_NAME; LEN] = [
+            WHvX64RegisterXmm0,
+            WHvX64RegisterXmm1,
+            WHvX64RegisterXmm2,
+            WHvX64RegisterXmm3,
+            WHvX64RegisterXmm4,
+            WHvX64RegisterXmm5,
+            WHvX64RegisterXmm6,
+            WHvX64RegisterXmm7,
+            WHvX64RegisterXmm8,
+            WHvX64RegisterXmm9,
+            WHvX64RegisterXmm10,
+            WHvX64RegisterXmm11,
+            WHvX64RegisterXmm12,
+            WHvX64RegisterXmm13,
+            WHvX64RegisterXmm14,
+            WHvX64RegisterXmm15,
+            WHvX64RegisterFpMmx0,
+            WHvX64RegisterFpMmx1,
+            WHvX64RegisterFpMmx2,
+            WHvX64RegisterFpMmx3,
+            WHvX64RegisterFpMmx4,
+            WHvX64RegisterFpMmx5,
+            WHvX64RegisterFpMmx6,
+            WHvX64RegisterFpMmx7,
+            WHvX64RegisterFpControlStatus,
+            WHvX64RegisterXmmControlStatus,
+        ];
+
+        let mut out: [WHV_REGISTER_VALUE; LEN] = unsafe { std::mem::zeroed() };
+        unsafe {
+            WHvGetVirtualProcessorRegisters(
+                self.get_partition_hdl(),
+                0,
+                names.as_ptr(),
+                LEN as u32,
+                out.as_mut_ptr(),
+            )?;
+        }
+
+        // Helper to read a WHV_UINT128 -> u128
+        fn u128_from_whv(fp: WHV_REGISTER_VALUE) -> u128 {
+            unsafe {
+                let low = fp.Fp.AsUINT128.Anonymous.Low64 as u128;
+                let high = fp.Fp.AsUINT128.Anonymous.High64 as u128;
+                (high << 64) | low
+            }
+        }
+
+        let xmm = [
+            u128_from_whv(out[0]),
+            u128_from_whv(out[1]),
+            u128_from_whv(out[2]),
+            u128_from_whv(out[3]),
+            u128_from_whv(out[4]),
+            u128_from_whv(out[5]),
+            u128_from_whv(out[6]),
+            u128_from_whv(out[7]),
+            u128_from_whv(out[8]),
+            u128_from_whv(out[9]),
+            u128_from_whv(out[10]),
+            u128_from_whv(out[11]),
+            u128_from_whv(out[12]),
+            u128_from_whv(out[13]),
+            u128_from_whv(out[14]),
+            u128_from_whv(out[15]),
+        ];
+
+        let mmx = [
+            out[16].Reg64,
+            out[17].Reg64,
+            out[18].Reg64,
+            out[19].Reg64,
+            out[20].Reg64,
+            out[21].Reg64,
+            out[22].Reg64,
+            out[23].Reg64,
+        ];
+
+        let fp_control_word = unsafe { out[24].FpControlStatus.Anonymous.FpControl };
+        let fp_tag_word = unsafe { out[24].FpControlStatus.Anonymous.FpTag };
+        let mxcsr = unsafe { out[25].XmmControlStatus.Anonymous.XmmStatusControl };
+
+        Ok(WHvFPURegisters {
+            xmm0: xmm[0],
+            xmm1: xmm[1],
+            xmm2: xmm[2],
+            xmm3: xmm[3],
+            xmm4: xmm[4],
+            xmm5: xmm[5],
+            xmm6: xmm[6],
+            xmm7: xmm[7],
+            xmm8: xmm[8],
+            xmm9: xmm[9],
+            xmm10: xmm[10],
+            xmm11: xmm[11],
+            xmm12: xmm[12],
+            xmm13: xmm[13],
+            xmm14: xmm[14],
+            xmm15: xmm[15],
+            mmx0: mmx[0],
+            mmx1: mmx[1],
+            mmx2: mmx[2],
+            mmx3: mmx[3],
+            mmx4: mmx[4],
+            mmx5: mmx[5],
+            mmx6: mmx[6],
+            mmx7: mmx[7],
+            fp_control_word,
+            fp_tag_word,
+            mxcsr,
+        })
+    }
+
     #[instrument(err(Debug), skip_all, parent = Span::current(), level= "Trace")]
     pub(super) fn run(&mut self) -> Result<WHV_RUN_VP_EXIT_CONTEXT> {
         let partition_handle = self.get_partition_hdl();