Re: [PATCH v3.5 3/4] tools/xen-cpuid: Use automatically generated feature names

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 20/05/2024 4:07 pm, Roger Pau Monné wrote:
> On Mon, May 20, 2024 at 03:33:59PM +0100, Andrew Cooper wrote:
>> From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>>
>> Have gen-cpuid.py write out INIT_FEATURE_VAL_TO_NAME, derived from the same
>> data source as INIT_FEATURE_NAME_TO_VAL, although both aliases of common_1d
>> are needed.
>>
>> In xen-cpuid.c, sanity check at build time that leaf_info[] and
>> feature_names[] are of sensible length.
>>
>> As dump_leaf() rendered missing names as numbers, always dump leaves even if
>> we don't have the leaf name.  This conversion was argumably missed in commit
>> 59afdb8a81d6 ("tools/misc: Tweak reserved bit handling for xen-cpuid").
>>
>> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Thanks.

>
> Just one question below.
>
>> ---
>> CC: Jan Beulich <JBeulich@xxxxxxxx>
>> CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>>
>> Differences in names are:
>>
>>  sysenter    -> sep
>>  tm          -> tm1
>>  ds-cpl      -> dscpl
>>  est         -> eist
>>  sse41       -> sse4-1
>>  sse42       -> sse4-2
>>  movebe      -> movbe
>>  tsc-dl      -> tsc-deadline
>>  rdrnd       -> rdrand
>>  hyper       -> hypervisor
>>  mmx+        -> mmext
>>  fxsr+       -> ffxsr
>>  pg1g        -> page1gb
>>  3dnow+      -> 3dnowext
>>  cmp         -> cmp-legacy
>>  cr8d        -> cr8-legacy
>>  lzcnt       -> abm
>>  msse        -> misalignsse
>>  3dnowpf     -> 3dnowprefetch
>>  nodeid      -> nodeid-msr
>>  dbx         -> dbext
>>  tsc-adj     -> tsc-adjust
>>  fdp-exn     -> fdp-excp-only
>>  deffp       -> no-fpu-sel
>>  <24>        -> bld
>>  ppin        -> amd-ppin
>>  lfence+     -> lfence-dispatch
>>  ppin        -> intel-ppin
>>  energy-ctrl -> energy-filtering
>>
>> Apparently BLD missed the update to xen-cpuid.c.  It appears to be the only
>> one.  Several of the + names would be nice to keep as were, but doing so 
>> isn't
>> nice in gen-cpuid.  Any changes would alter the {dom0-}cpuid= cmdline 
>> options,
>> but we intentionally don't list them, so I'm not worried.
>>
>> Thoughts?
>>
>> v3:
>>  * Rework somewhat.
>>  * Insert aliases of common_1d.
>>
>> v4:
>>  * Pad at the gen stage.  I don't like this, but I'm clearly outvoted on the 
>> matter.
>> ---
>>  tools/misc/xen-cpuid.c | 16 ++++++++--------
>>  xen/tools/gen-cpuid.py | 29 +++++++++++++++++++++++++++++
>>  2 files changed, 37 insertions(+), 8 deletions(-)
>>
>> diff --git a/tools/misc/xen-cpuid.c b/tools/misc/xen-cpuid.c
>> index 6ee835b22949..51009683da1b 100644
>> --- a/tools/misc/xen-cpuid.c
>> +++ b/tools/misc/xen-cpuid.c
>> @@ -11,6 +11,7 @@
>>  #include <xenguest.h>
>>  
>>  #include <xen-tools/common-macros.h>
>> +#include <xen/lib/x86/cpuid-autogen.h>
>>  
>>  static uint32_t nr_features;
>>  
>> @@ -291,6 +292,8 @@ static const struct {
>>  
>>  #define COL_ALIGN "24"
>>  
>> +static const char *const feature_names[] = INIT_FEATURE_VAL_TO_NAME;
>> +
>>  static const char *const fs_names[] = {
>>      [XEN_SYSCTL_cpu_featureset_raw]     = "Raw",
>>      [XEN_SYSCTL_cpu_featureset_host]    = "Host",
>> @@ -304,12 +307,6 @@ static void dump_leaf(uint32_t leaf, const char *const 
>> *strs)
>>  {
>>      unsigned i;
>>  
>> -    if ( !strs )
>> -    {
>> -        printf(" ???");
>> -        return;
>> -    }
>> -
>>      for ( i = 0; i < 32; ++i )
>>          if ( leaf & (1u << i) )
>>          {
>> @@ -327,6 +324,10 @@ static void decode_featureset(const uint32_t *features,
>>  {
>>      unsigned int i;
>>  
>> +    /* If this trips, you probably need to extend leaf_info[] above. */
>> +    BUILD_BUG_ON(ARRAY_SIZE(leaf_info) != FEATURESET_NR_ENTRIES);
>> +    BUILD_BUG_ON(ARRAY_SIZE(feature_names) != FEATURESET_NR_ENTRIES * 32);
>> +
>>      printf("%-"COL_ALIGN"s        ", name);
>>      for ( i = 0; i < length; ++i )
>>          printf("%08x%c", features[i],
>> @@ -338,8 +339,7 @@ static void decode_featureset(const uint32_t *features,
>>      for ( i = 0; i < length && i < ARRAY_SIZE(leaf_info); ++i )
>>      {
>>          printf("  [%02u] %-"COL_ALIGN"s", i, leaf_info[i].name ?: 
>> "<UNKNOWN>");
>> -        if ( leaf_info[i].name )
>> -            dump_leaf(features[i], leaf_info[i].strs);
>> +        dump_leaf(features[i], &feature_names[i * 32]);
>>          printf("\n");
>>      }
>>  }
>> diff --git a/xen/tools/gen-cpuid.py b/xen/tools/gen-cpuid.py
>> index 79d7f5c8e1c9..601eec608983 100755
>> --- a/xen/tools/gen-cpuid.py
>> +++ b/xen/tools/gen-cpuid.py
>> @@ -470,6 +470,35 @@ def write_results(state):
>>      state.output.write(
>>  """}
>>  
>> +""")
>> +
>> +    state.output.write(
>> +"""
>> +#define INIT_FEATURE_VAL_TO_NAME { \\
>> +""")
>> +
>> +    for name, bit in sorted(state.values.items()):
>> +        state.output.write(
>> +            '    [%s] = "%s",\\\n' % (bit, name)
>> +            )
>> +
>> +        # Add the other alias for 1d/e1d common bits.  64 is the difference
>> +        # between 1d and e1d.
>> +        if bit in state.common_1d:
>> +            state.output.write(
>> +                '    [%s] = "%s",\\\n' % (64 + bit, name)
>> +            )
>> +
>> +    # Pad to an exact multiple of FEATURESET_SIZE if necessary
>> +    pad_feat = state.nr_entries * 32 - 1
>> +    if not state.names.get(pad_feat):
>> +        state.output.write(
>> +            '    [%s] = NULL,\\\n' % (pad_feat, )
> One likely stupid question, but since my understanding of Python is
> very limited, why do you add the comma after pad_feat?  There's no
> other parameter to print.

It's a common python gotcha with %.

>>> a = (1, 2)
>>> "%s" % a
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: not all arguments converted during string formatting
>>> "%s" % (a, )
'(1, 2)'

You should always pass % a tuple, even a 1-element tuple, so it does the
right thing when you're not sure of the type of the thing being printed.

~Andrew