hypervisor: emulator: Format instructions on error paths

Formatting instructions might be costly, so we only want to do that on
the emulation error paths.

Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

hypervisor/Cargo.toml

@@ -28,7 +28,7 @@ features = ["elf", "bzimage"]
 [dependencies.iced-x86]
 version = "1.9.1"
 default-features = false
-features = ["std", "decoder", "op_code_info", "instr_info"]
+features = ["std", "decoder", "op_code_info", "instr_info", "fast_fmt"]
 
 [dev-dependencies]
 env_logger = "0.8.2"

hypervisor/src/arch/emulator/mod.rs

@@ -76,6 +76,9 @@ pub enum EmulationError<T: Debug> {
 
     #[error("Platform emulation error: {0}")]
     PlatformEmulationError(PlatformError),
+
+    #[error(transparent)]
+    EmulationError(#[from] anyhow::Error),
 }
 
 /// The PlatformEmulator trait emulates a guest platform.

hypervisor/src/arch/x86/emulator/instructions/mod.rs

@@ -114,3 +114,16 @@ macro_rules! insn_add {
         $insn_map.add_insn(Code::$code, Box::new($mnemonic::$code {}));
     };
 }
+
+macro_rules! insn_format {
+    ($insn:ident) => {{
+        let mut output = String::new();
+        let mut formatter = FastFormatter::new();
+        formatter
+            .options_mut()
+            .set_space_after_operand_separator(true);
+        formatter.format(&$insn, &mut output);
+
+        output
+    }};
+}

hypervisor/src/arch/x86/emulator/mod.rs

@@ -12,6 +12,7 @@ use crate::arch::x86::regs::*;
 use crate::arch::x86::*;
 use crate::arch::x86::{Exception, SegmentRegisterOps};
 use crate::x86_64::{SegmentRegister, SpecialRegisters, StandardRegisters};
+use anyhow::Context;
 use iced_x86::*;
 
 #[macro_use]
@@ -551,7 +552,8 @@ impl<'a, T: CpuStateManager> Emulator<'a, T> {
                 decoder.decode_out(&mut insn);
                 if decoder.last_error() != DecoderError::None {
                     return Err(EmulationError::InstructionFetchingError(anyhow!(
-                        "{:#x?}", insn
+                        "{:#x?}",
+                        insn_format!(insn)
                     )));
                 }
 
@@ -563,9 +565,15 @@ impl<'a, T: CpuStateManager> Emulator<'a, T> {
                 .instructions
                 .get(&insn.code())
                 .ok_or_else(|| {
-                    EmulationError::UnsupportedInstruction(anyhow!("{:?}", insn.mnemonic()))
+                    EmulationError::UnsupportedInstruction(anyhow!(
+                        "{:#x?} {:?} {:?}",
+                        insn_format!(insn),
+                        insn.mnemonic(),
+                        insn.code()
+                    ))
                 })?
-                .emulate(&insn, &mut state, self.platform)?;
+                .emulate(&insn, &mut state, self.platform)
+                .context(anyhow!("Failed to emulate {:#x?}", insn_format!(insn)))?;
 
             last_decoded_ip = decoder.ip();
             num_insn_emulated += 1;