x86_64: implement error trait for sub-modules in x86_64 crate

Implement the std::error::Error Trait for Error types within the
x86_64 crate.  We will make use of these implementations later on when
we are using the architecture Trait to pass architecture-specific
errors up with meaningful descriptions.

BUG=chromium:797868
TEST=./build_test passes on all architectures
TEST=crosvm runs on caroline

Change-Id: I7a30db69437990608e3a0f5e6e3a200ef6c2d0c3
Reviewed-on: https://chromium-review.googlesource.com/932976
Commit-Ready: Sonny Rao <sonnyrao@chromium.org>
Tested-by: Sonny Rao <sonnyrao@chromium.org>
Reviewed-by: Sonny Rao <sonnyrao@chromium.org>

4 files changed, 98 insertions, 0 deletions

diff --git a/x86_64/src/cpuid.rs b/x86_64/src/cpuid.rs
index a23d24b..f1c7b56 100644
--- a/x86_64/src/cpuid.rs
+++ b/x86_64/src/cpuid.rs
@@ -3,6 +3,8 @@
 // found in the LICENSE file.
 
 use std::result;
+use std::fmt::{self, Display};
+use std::error::{self, Error as CpuidError};
 
 use kvm;
 use sys_util;
@@ -18,6 +20,23 @@ pub enum Error {
 }
 pub type Result<T> = result::Result<T, Error>;
 
+impl error::Error for Error {
+    fn description(&self) -> &str {
+        match self {
+            &Error::GetSupportedCpusFailed(_) =>
+                "GetSupportedCpus ioctl failed",
+            &Error::SetSupportedCpusFailed(_) =>
+                "SetSupportedCpus ioctl failed",
+        }
+    }
+}
+
+impl Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "CPUID Error: {}", Error::description(self))
+    }
+}
+
 // CPUID bits in ebx, ecx, and edx.
 const EBX_CLFLUSH_CACHELINE: u32 = 8; // Flush a cache line size.
 const EBX_CLFLUSH_SIZE_SHIFT: u32 = 8; // Bytes flushed when executing CLFLUSH.
diff --git a/x86_64/src/interrupts.rs b/x86_64/src/interrupts.rs
index 72ba2e9..65bc621 100644
--- a/x86_64/src/interrupts.rs
+++ b/x86_64/src/interrupts.rs
@@ -5,6 +5,8 @@
 use std::io::Cursor;
 use std::mem;
 use std::result;
+use std::error::{self, Error as InterruptsError};
+use std::fmt::{self, Display};
 
 use byteorder::{LittleEndian, ReadBytesExt, WriteBytesExt};
 
@@ -19,6 +21,21 @@ pub enum Error {
 }
 pub type Result<T> = result::Result<T, Error>;
 
+impl error::Error for Error {
+    fn description(&self) -> &str {
+        match self {
+            &Error::GetLapic(_) => "GetLapic ioctl failed",
+            &Error::SetLapic(_) => "SetLapic ioctl failed",
+        }
+    }
+}
+
+impl Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "Interrupt Error: {}", Error::description(self))
+    }
+}
+
 // Defines poached from apicdef.h kernel header.
 const APIC_LVT0: usize = 0x350;
 const APIC_LVT1: usize = 0x360;
diff --git a/x86_64/src/mptable.rs b/x86_64/src/mptable.rs
index fea1622..d433433 100644
--- a/x86_64/src/mptable.rs
+++ b/x86_64/src/mptable.rs
@@ -6,6 +6,8 @@ use std::io;
 use std::mem;
 use std::result;
 use std::slice;
+use std::error::{self, Error as MptableError};
+use std::fmt::{self, Display};
 
 use libc::c_char;
 
@@ -37,6 +39,32 @@ pub enum Error {
     WriteMpcTable,
 }
 
+impl error::Error for Error {
+    fn description(&self) -> &str {
+        match self {
+            &Error::NotEnoughMemory =>
+                "There was too little guest memory to store the MP table",
+            &Error::AddressOverflow =>
+                "The MP table has too little address space to be stored",
+            &Error::Clear => "Failure while zeroing out the memory for the MP table",
+            &Error::WriteMpfIntel => "Failure to write the MP floating pointer",
+            &Error::WriteMpcCpu => "Failure to write MP CPU entry",
+            &Error::WriteMpcIoapic => "Failure to write MP ioapic entry",
+            &Error::WriteMpcBus => "Failure to write MP bus entry",
+            &Error::WriteMpcIntsrc => "Failure to write MP interrupt source entry",
+            &Error::WriteMpcLintsrc =>
+                "Failure to write MP local interrupt source entry",
+            &Error::WriteMpcTable => "Failure to write MP table header",
+        }
+    }
+}
+
+impl Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "MPTable Error: {}", Error::description(self))
+    }
+}
+
 pub type Result<T> = result::Result<T, Error>;
 
 // Convenience macro for making arrays of diverse character types.
diff --git a/x86_64/src/regs.rs b/x86_64/src/regs.rs
index d43c899..31b6bab 100644
--- a/x86_64/src/regs.rs
+++ b/x86_64/src/regs.rs
@@ -3,6 +3,8 @@
 // found in the LICENSE file.
 
 use std::{mem, result};
+use std::error::{self, Error as RegsError};
+use std::fmt::{self, Display};
 
 use kvm;
 use kvm_sys::kvm_fpu;
@@ -37,6 +39,38 @@ pub enum Error {
 }
 pub type Result<T> = result::Result<T, Error>;
 
+impl error::Error for Error {
+    fn description(&self) -> &str {
+        match self {
+            &Error::MsrIoctlFailed(_) =>
+                "Setting up msrs failed",
+            &Error::FpuIoctlFailed(_) =>
+                "Failed to configure the FPU",
+            &Error::SettingRegistersIoctl(_) =>
+                "Failed to set base registers for this cpu",
+            &Error::SRegsIoctlFailed(_) =>
+                "Failed to set sregs for this cpu",
+            &Error::WriteGDTFailure =>
+                "Writing the GDT to RAM failed",
+            &Error::WriteIDTFailure =>
+                "Writing the IDT to RAM failed",
+            &Error::WritePML4Address =>
+                "Writing PML4 to RAM failed",
+            &Error::WritePDPTEAddress =>
+                "Writing PDPTE to RAM failed",
+            &Error::WritePDEAddress =>
+                "Writing PDE to RAM failed",
+
+        }
+    }
+}
+
+impl Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "Interrupt Error: {}", Error::description(self))
+    }
+}
+
 fn create_msr_entries() -> Vec<kvm_msr_entry> {
     let mut entries = Vec::<kvm_msr_entry>::new();