[Xen-devel] [PATCH v2 0.5/8] libx86: Proactively initialise error pointers

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

This results in better behaviour for the caller.

Suggested-by: Jan Beulich <JBeulich@xxxxxxxx>
Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>

v2:
 * New
---
 tools/tests/cpu-policy/test-cpu-policy.c | 4 ++--
 xen/include/xen/lib/x86/cpuid.h          | 6 +++---
 xen/include/xen/lib/x86/msr.h            | 4 ++--
 xen/lib/x86/cpuid.c                      | 5 +++++
 xen/lib/x86/msr.c                        | 3 +++
 5 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/tools/tests/cpu-policy/test-cpu-policy.c 
b/tools/tests/cpu-policy/test-cpu-policy.c
index fe00cd4276..201358d210 100644
--- a/tools/tests/cpu-policy/test-cpu-policy.c
+++ b/tools/tests/cpu-policy/test-cpu-policy.c
@@ -283,7 +283,7 @@ static void test_cpuid_deserialise_failure(void)
     for ( size_t i = 0; i < ARRAY_SIZE(tests); ++i )
     {
         const struct test *t = &tests[i];
-        uint32_t err_leaf = ~0u, err_subleaf = ~0u;
+        uint32_t err_leaf, err_subleaf;
         int rc;
 
         /* No writes should occur.  Use NULL to catch errors. */
@@ -336,7 +336,7 @@ static void test_msr_deserialise_failure(void)
     for ( size_t i = 0; i < ARRAY_SIZE(tests); ++i )
     {
         const struct test *t = &tests[i];
-        uint32_t err_msr = ~0u;
+        uint32_t err_msr;
         int rc;
 
         /* No writes should occur.  Use NULL to catch errors. */
diff --git a/xen/include/xen/lib/x86/cpuid.h b/xen/include/xen/lib/x86/cpuid.h
index df5946b6b1..79840f99ce 100644
--- a/xen/include/xen/lib/x86/cpuid.h
+++ b/xen/include/xen/lib/x86/cpuid.h
@@ -376,13 +376,13 @@ int x86_cpuid_copy_to_buffer(const struct cpuid_policy 
*policy,
  * @param policy      The cpuid_policy to unserialise into.
  * @param leaves      The array of leaves to unserialise from.
  * @param nr_entries  The number of entries in 'leaves'.
- * @param err_leaf    Optional hint filled on error.
- * @param err_subleaf Optional hint filled on error.
+ * @param err_leaf    Optional hint for error diagnostics.
+ * @param err_subleaf Optional hint for error diagnostics.
  * @returns -errno
  *
  * Reads at most CPUID_MAX_SERIALISED_LEAVES.  May return -ERANGE if an
  * incoming leaf is out of range of cpuid_policy, in which case the optional
- * err_* pointers are filled to aid diagnostics.
+ * err_* pointers will identify the out-of-range indicies.
  *
  * No content validation of in-range leaves is performed.  Synthesised data is
  * recalculated.
diff --git a/xen/include/xen/lib/x86/msr.h b/xen/include/xen/lib/x86/msr.h
index e83a8fbb0f..203c713320 100644
--- a/xen/include/xen/lib/x86/msr.h
+++ b/xen/include/xen/lib/x86/msr.h
@@ -54,14 +54,14 @@ int x86_msr_copy_to_buffer(const struct msr_policy *policy,
  * @param policy     The msr_policy object to unserialise into.
  * @param msrs       The array of msrs to unserialise from.
  * @param nr_entries The number of entries in 'msrs'.
- * @param err_msr    Optional hint filled on error.
+ * @param err_msr    Optional hint for error diagnostics.
  * @returns -errno
  *
  * Reads at most MSR_MAX_SERIALISED_ENTRIES.  May fail for a number of reasons
  * based on the content in an individual 'msrs' entry, including the MSR index
  * not being valid in the policy, the flags field being nonzero, or if the
  * value provided would truncate when stored in the policy.  In such cases,
- * the optional err_* pointer is filled in to aid diagnostics.
+ * the optional err_* pointer will identify the problematic MSR.
  *
  * No content validation is performed on the data stored in the policy object.
  */
diff --git a/xen/lib/x86/cpuid.c b/xen/lib/x86/cpuid.c
index 266084e613..76b8511034 100644
--- a/xen/lib/x86/cpuid.c
+++ b/xen/lib/x86/cpuid.c
@@ -381,6 +381,11 @@ int x86_cpuid_copy_from_buffer(struct cpuid_policy *p,
     unsigned int i;
     xen_cpuid_leaf_t data;
 
+    if ( err_leaf )
+        *err_leaf = -1;
+    if ( err_subleaf )
+        *err_subleaf = -1;
+
     /*
      * A well formed caller is expected to pass an array with leaves in order,
      * and without any repetitions.  However, due to per-vendor differences,
diff --git a/xen/lib/x86/msr.c b/xen/lib/x86/msr.c
index 256b5ec632..171abf7008 100644
--- a/xen/lib/x86/msr.c
+++ b/xen/lib/x86/msr.c
@@ -55,6 +55,9 @@ int x86_msr_copy_from_buffer(struct msr_policy *p,
     xen_msr_entry_t data;
     int rc;
 
+    if ( err_msr )
+        *err_msr = -1;
+
     /*
      * A well formed caller is expected to pass an array with entries in
      * order, and without any repetitions.  However, due to per-vendor
-- 
2.11.0


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