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Message-ID: <ZwVTVO2FcH95WFBp@lx-t490>
Date: Tue, 8 Oct 2024 17:44:20 +0200
From: "Ahmed S. Darwish" <darwi@...utronix.de>
To: Andrew Cooper <andrew.cooper3@...rix.com>
Cc: x86-cpuid@...ts.linux.dev, Borislav Petkov <bp@...en8.de>,
"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
Thomas Gleixner <tglx@...utronix.de>,
Sohil Mehta <sohil.mehta@...el.com>,
John Ogness <john.ogness@...utronix.de>,
linux-kernel@...r.kernel.org
Subject: Re: [ANNOUNCE] x86-cpuid-db: Release v2.0
Hi Andrew,
On Tue, 08 Oct 2024, Andrew Cooper wrote:
>
> On 08/10/2024 2:31 pm, Ahmed S. Darwish wrote:
> > to:
> >
> > /*
> > * Leaf 0x0
> > * Maximum standard leaf number + CPU vendor string
> > */
> >
> > struct leaf_0x0_0 {
> > ...;
> > };
> >
> > /*
> > * Leaf 0x7
> > * Extended CPU features enumeration
> > */
> >
> > struct leaf_0x7_0 {
> > ...;
> > };
> >
> > struct leaf_0x7_1 {
> > ...;
> > };
> >
> > Overall, this removes ambiguity for IDs like 0x16, and improves kernel
> > code greppability (x86 PQ pending).
>
> So what does leaf 0xd with 62 subleaves look like. Do we really have
> one number in hex, and one in decimal?
Hmmm, good point...
For now, if we grep the generated C linux header for all the structures
that are not subleaf 0, we get:
$ grep -E 'struct leaf_0x[0-9a-f]+_[^0]' cpuid-bitfields.h
struct leaf_0x7_1 {
struct leaf_0x7_2 {
struct leaf_0xd_1 {
struct leaf_0xd_2 {
struct leaf_0xf_1 {
struct leaf_0x10_1 {
struct leaf_0x10_3 {
struct leaf_0x12_1 {
struct leaf_0x12_2 {
struct leaf_0x14_1 {
struct leaf_0x17_1 {
struct leaf_0x1d_1 {
struct leaf_0x23_1 {
struct leaf_0x23_3 {
struct leaf_0x80000020_1 {
struct leaf_0x80000020_2 {
struct leaf_0x80000020_3 {
We do indeed have an encodings for leaves with large dynamic number of
valid subleaves, through "array=":
darwi@lx ~/x86-cpuid-db (main)> git grep array=
db/xml/leaf_04.xml: <subleaf id="0" array="32">
db/xml/leaf_0b.xml: <subleaf id="0" array="2">
db/xml/leaf_0d.xml: <subleaf id="2" array="62">
db/xml/leaf_10.xml: <subleaf id="1" array="2">
db/xml/leaf_12.xml: <subleaf id="2" array="30">
db/xml/leaf_17.xml: <subleaf id="1" array="3">
db/xml/leaf_18.xml: <subleaf id="0" array="32">
db/xml/leaf_1b.xml: <subleaf id="0" array="32">
db/xml/leaf_1f.xml: <subleaf id="0" array="6">
db/xml/leaf_8000001d.xml: <subleaf id="0" array="32">
db/xml/leaf_80000026.xml: <subleaf id="0" array="4">
But the generators don't deal with that (yet), and that's why they're
also not in the generated CSV/header files.
I'm going through the Linux x86 PQ now, so it's a nice opportunity to
see how something like "struct leaf_0x0_0x0" looks within the rest of
the kernel code... I'll also ping Thomas to see if he has any feedback
on the topic.
Thanks!
--
Ahmed S. Darwish
Linutronix GmbH
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