[PATCH][RFC] PentiumPro/II split in x86 config

[PATCH][RFC] PentiumPro/II split in x86 config

[J.A. Magallon]

Hello.

Patch below splits the config build option for PentiumPro and PentiumII
to make them different, so gcc (see next patch) can generate pII
specific code. It also kills the lock errata protection in PII code, so
it only applies to PPro, not PII.

Due to Alan's advice, it also adds a check that will panic if a PII or
higher kernel is run on a PPro or lesser (plz, I put that code in the
place I thought it was the best, but probably I'm wrong...).

It still keeps -march=i686. I will change it on a next patch.

Comments ?

Patch follows (91-split-ppro-config):

--- linux-2.4.18/arch/i386/Makefile.orig	2002-05-26 01:26:40.000000000 +0200
+++ linux-2.4.18/arch/i386/Makefile	2002-05-26 01:28:52.000000000 +0200
@@ -50,6 +50,10 @@
 CFLAGS += -march=i686
 endif
 
+ifdef CONFIG_MPENTIUMII
+CFLAGS += -march=i686
+endif
+
 ifdef CONFIG_MPENTIUMIII
 CFLAGS += -march=i686
 endif
--- linux-2.4.18/arch/i386/config.in.orig	2002-05-26 01:29:01.000000000 +0200
+++ linux-2.4.18/arch/i386/config.in	2002-05-26 01:29:41.000000000 +0200
@@ -32,7 +32,8 @@
 	 586/K5/5x86/6x86/6x86MX		CONFIG_M586 \
 	 Pentium-Classic			CONFIG_M586TSC \
 	 Pentium-MMX				CONFIG_M586MMX \
-	 Pentium-Pro/Celeron/Pentium-II		CONFIG_M686 \
+	 Pentium-Pro			CONFIG_M686 \
+	 Pentium-II/Celeron		CONFIG_MPENTIUMII \
 	 Pentium-III/Celeron(Coppermine)	CONFIG_MPENTIUMIII \
 	 Pentium-4				CONFIG_MPENTIUM4 \
 	 K6/K6-II/K6-III			CONFIG_MK6 \
@@ -99,6 +99,13 @@
    define_bool CONFIG_X86_USE_PPRO_CHECKSUM y
    define_bool CONFIG_X86_PPRO_FENCE y
 fi
+if [ "$CONFIG_MPENTIUMII" = "y" ]; then
+   define_int  CONFIG_X86_L1_CACHE_SHIFT 5
+   define_bool CONFIG_X86_TSC y
+   define_bool CONFIG_X86_GOOD_APIC y
+   define_bool CONFIG_X86_PGE y
+   define_bool CONFIG_X86_USE_PPRO_CHECKSUM y
+fi
 if [ "$CONFIG_MPENTIUMIII" = "y" ]; then
    define_int  CONFIG_X86_L1_CACHE_SHIFT 5
    define_bool CONFIG_X86_TSC y
--- linux-2.4.18/arch/i386/defconfig.orig	2002-05-26 01:34:19.000000000 +0200
+++ linux-2.4.18/arch/i386/defconfig	2002-05-26 01:34:48.000000000 +0200
@@ -27,6 +27,7 @@
 # CONFIG_M586TSC is not set
 # CONFIG_M586MMX is not set
 # CONFIG_M686 is not set
+# CONFIG_MPENTIUMII is not set
 CONFIG_MPENTIUMIII=y
 # CONFIG_MPENTIUM4 is not set
 # CONFIG_MK6 is not set
--- linux/arch/i386/kernel/setup.c.orig	2002-05-27 00:32:58.000000000 +0200
+++ linux/arch/i386/kernel/setup.c	2002-05-27 00:46:36.000000000 +0200
@@ -2092,6 +2092,14 @@
 
 extern void trap_init_f00f_bug(void);
 
+static void __init check_intel_compat(struct cpuinfo_x86 *c)
+{
+#if defined(CONFIG_MPENTIUMII) || defined(CONFIG_MPENTIUMIII) || defined(CONFIG_MPENTIUM4)
+	if (c->x86 <= 5)
+		panic("Kernel is unsafe/incompatible with this CPU model. Check your build settings !\n");
+#endif
+}
+
 static void __init init_intel(struct cpuinfo_x86 *c)
 {
 #ifndef CONFIG_M686
@@ -2100,6 +2108,8 @@
 	char *p = NULL;
 	unsigned int l1i = 0, l1d = 0, l2 = 0, l3 = 0; /* Cache sizes */
 
+	check_intel_compat(c);
+
 #ifndef CONFIG_M686
 	/*
 	 * All current models of Pentium and Pentium with MMX technology CPUs

-- 
J.A. Magallon                           #  Let the source be with you...        
mailto:jamagallon@able.es
Mandrake Linux release 8.3 (Cooker) for i586
Linux werewolf 2.4.19-pre8-jam4 #2 SMP dom may 26 11:20:42 CEST 2002 i686

Re: [PATCH][RFC] PentiumPro/II split in x86 config

[Alan Cox]

On Mon, 2002-05-27 at 15:54, J.A. Magallon wrote:

> +static void __init check_intel_compat(struct cpuinfo_x86 *c)
> +{
> +#if defined(CONFIG_MPENTIUMII) || defined(CONFIG_MPENTIUMIII) || defined(CONFIG_MPENTIUM4)
> +	if (c->x86 <= 5)
> +		panic("Kernel is unsafe/incompatible with this CPU model. Check your build settings !\n");
> +#endif

The PPro is also model 6 but a different family (1 if I remember
rightly)

Re: [PATCH][RFC] PentiumPro/II split in x86 config

[J.A. Magallon]

On 2002.05.27 Alan Cox wrote:
>On Mon, 2002-05-27 at 15:54, J.A. Magallon wrote:
>
>> +static void __init check_intel_compat(struct cpuinfo_x86 *c)
>> +{
>> +#if defined(CONFIG_MPENTIUMII) || defined(CONFIG_MPENTIUMIII) || defined(CONFIG_MPENTIUM4)
>> +	if (c->x86 <= 5)
>> +		panic("Kernel is unsafe/incompatible with this CPU model. Check your build settings !\n");
>> +#endif
>
>The PPro is also model 6 but a different family (1 if I remember
>rightly)
>

Opps... typo.
Yes:

    { X86_VENDOR_INTEL, 6,
      { "Pentium Pro A-step", "Pentium Pro", NULL, "Pentium II (Klamath)",
        NULL, "Pentium II (Deschutes)", "Mobile Pentium II",
        "Pentium III (Katmai)", "Pentium III (Coppermine)", NULL,
        "Pentium III (Cascades)", NULL, NULL, NULL, NULL }},

Corrected patch on the way...

-- 
J.A. Magallon                           #  Let the source be with you...        
mailto:jamagallon@able.es
Mandrake Linux release 8.3 (Cooker) for i586
Linux werewolf 2.4.19-pre8-jam4 #2 SMP dom may 26 11:20:42 CEST 2002 i686

Re: [PATCH][RFC] PentiumPro/II split in x86 config

[Arnaldo Carvalho de Melo]

Em Mon, May 27, 2002 at 11:59:11PM +0200, J.A. Magallon escreveu:
> Opps... typo.
> Yes:
> 
>     { X86_VENDOR_INTEL, 6,
>       { "Pentium Pro A-step", "Pentium Pro", NULL, "Pentium II (Klamath)",
>         NULL, "Pentium II (Deschutes)", "Mobile Pentium II",
>         "Pentium III (Katmai)", "Pentium III (Coppermine)", NULL,
>         "Pentium III (Cascades)", NULL, NULL, NULL, NULL }},
> 
> Corrected patch on the way...

Hi,

	Since you're working on this could I suggest that you use labeled
elements, this gccism make the initialization above way more cleaner, safer and
easy to read :-) This is being used in the kernel in places like the FSes, the
TCP/IP stack and lots of other places.

	We don't need all the NULLs, as uninitialized entries will be zeroed
out by the compiler.

	Here is how it would look like:

--- 1.50/arch/i386/kernel/setup.c	Sat Apr 27 14:47:46 2002
+++ edited/arch/i386/kernel/setup.c	Mon May 27 22:03:35 2002
@@ -2245,15 +2245,34 @@
 /* This table only is used unless init_<vendor>() below doesn't set it; */
 /* in particular, if CPUID levels 0x80000002..4 are supported, this isn't used */
 static struct cpu_model_info cpu_models[] __initdata = {
-	{ X86_VENDOR_INTEL,	4,
-	  { "486 DX-25/33", "486 DX-50", "486 SX", "486 DX/2", "486 SL", 
-	    "486 SX/2", NULL, "486 DX/2-WB", "486 DX/4", "486 DX/4-WB", NULL, 
-	    NULL, NULL, NULL, NULL, NULL }},
-	{ X86_VENDOR_INTEL,	5,
-	  { "Pentium 60/66 A-step", "Pentium 60/66", "Pentium 75 - 200",
-	    "OverDrive PODP5V83", "Pentium MMX", NULL, NULL,
-	    "Mobile Pentium 75 - 200", "Mobile Pentium MMX", NULL, NULL, NULL,
-	    NULL, NULL, NULL, NULL }},
+	{
+		vendor:	     X86_VENDOR_INTEL,
+		family:	     4,
+		model_names: {
+				[0] = "486 DX-25/33",
+				[1] = "486 DX-50",
+				[2] = "486 SX",
+				[3] = "486 DX/2",
+				[4] = "486 SL", 
+				[5] = "486 SX/2",
+				[7] = "486 DX/2-WB",
+				[8] = "486 DX/4",
+				[9] = "486 DX/4-WB",
+		},
+	},
+	{
+		vendor:	     X86_VENDOR_INTEL,
+		family:	     5,
+		model_names: {
+				[0] = "Pentium 60/66 A-step",
+				[1] = "Pentium 60/66",
+				[2] = "Pentium 75 - 200",
+				[3] = "OverDrive PODP5V83",
+				[4] = "Pentium MMX",
+				[7] = "Mobile Pentium 75 - 200",
+				[8] = "Mobile Pentium MMX",
+		}
+	},
 	{ X86_VENDOR_INTEL,	6,
 	  { "Pentium Pro A-step", "Pentium Pro", NULL, "Pentium II (Klamath)", 
 	    NULL, "Pentium II (Deschutes)", "Mobile Pentium II",

Best Regards,

- Arnaldo, with the janitor hat on for the time being 8)

Re: [PATCH][RFC] PentiumPro/II split in x86 config

[Keith Owens]

On Mon, 27 May 2002 22:29:25 -0300, 
Arnaldo Carvalho de Melo <acme@conectiva.com.br> wrote:
>	Since you're working on this could I suggest that you use labeled
>elements, this gccism make the initialization above way more cleaner, safer and
>easy to read :-) This is being used in the kernel in places like the FSes, the
>TCP/IP stack and lots of other places.
>+		vendor:	     X86_VENDOR_INTEL,
>+		family:	     5,

Better still, use the C language standard:

		.vendor = X86_VENDOR_INTEL,
		.family = 5,

Re: [PATCH][RFC] PentiumPro/II split in x86 config

[Arnaldo Carvalho de Melo]

Em Tue, May 28, 2002 at 12:05:54PM +1000, Keith Owens escreveu:
> On Mon, 27 May 2002 22:29:25 -0300, 
> Arnaldo Carvalho de Melo <acme@conectiva.com.br> wrote:
> >	Since you're working on this could I suggest that you use labeled
> >elements, this gccism make the initialization above way more cleaner, safer and
> >easy to read :-) This is being used in the kernel in places like the FSes, the
> >TCP/IP stack and lots of other places.
> >+		vendor:	     X86_VENDOR_INTEL,
> >+		family:	     5,
> 
> Better still, use the C language standard:
> 
> 		.vendor = X86_VENDOR_INTEL,
> 		.family = 5,

oops, gcc accepts that, good to know that this is standard C, but for the
kernel, I think that this doesn't matter as gcc is the only compiler that
understands the GCC Language 8) Or am I wrong? I'd love to be... 8)

- Arnaldo

Re: [PATCH][RFC] PentiumPro/II split in x86 config

[Keith Owens]

On Mon, 27 May 2002 23:16:47 -0300, 
Arnaldo Carvalho de Melo <acme@conectiva.com.br> wrote:
>Em Tue, May 28, 2002 at 12:05:54PM +1000, Keith Owens escreveu:
>> Better still, use the C language standard:
>> 
>> 		.vendor = X86_VENDOR_INTEL,
>
>oops, gcc accepts that, good to know that this is standard C, but for the
>kernel, I think that this doesn't matter as gcc is the only compiler that
>understands the GCC Language 8) Or am I wrong? I'd love to be... 8)

The kernel can only be compiled with gcc, but some bits of the build
are compiled and run on the host, using the host compiler.  Avoid using
gccisms where there is a standard way of doing it.

Re: [PATCH][RFC] PentiumPro/II split in x86 config

[Arnaldo Carvalho de Melo]

Em Tue, May 28, 2002 at 12:24:14PM +1000, Keith Owens escreveu:
> On Mon, 27 May 2002 23:16:47 -0300, 
> Arnaldo Carvalho de Melo <acme@conectiva.com.br> wrote:
> >Em Tue, May 28, 2002 at 12:05:54PM +1000, Keith Owens escreveu:
> >> Better still, use the C language standard:
> >> 
> >> 		.vendor = X86_VENDOR_INTEL,
> >
> >oops, gcc accepts that, good to know that this is standard C, but for the
> >kernel, I think that this doesn't matter as gcc is the only compiler that
> >understands the GCC Language 8) Or am I wrong? I'd love to be... 8)
> 
> The kernel can only be compiled with gcc, but some bits of the build
> are compiled and run on the host, using the host compiler.  Avoid using
> gccisms where there is a standard way of doing it.

I see, I was not thinking about those bits of the build, only kernel code, where
there are plenty of other gccisms.

/me will take a look at the latest C standard... :-)

- Arnaldo

Re: [PATCH][RFC] PentiumPro/II split in x86 config

[Miles Bader]

Keith Owens <kaos@ocs.com.au> writes:
> The kernel can only be compiled with gcc, but some bits of the build
> are compiled and run on the host, using the host compiler.  Avoid using
> gccisms where there is a standard way of doing it.

That particular gccism completely infests the kernel, so there seems
little point in avoiding it in favor of the uglier standard syntax.

-Miles
-- 
I have seen the enemy, and he is us.  -- Pogo

Re: [PATCH][RFC] PentiumPro/II split in x86 config

[Arnaldo Carvalho de Melo]

Em Tue, May 28, 2002 at 11:55:47AM +0900, Miles Bader escreveu:
> Keith Owens <kaos@ocs.com.au> writes:
> > The kernel can only be compiled with gcc, but some bits of the build
> > are compiled and run on the host, using the host compiler.  Avoid using
> > gccisms where there is a standard way of doing it.
> 
> That particular gccism completely infests the kernel, so there seems
> little point in avoiding it in favor of the uglier standard syntax.

Agreed.

What I'll do: continue using the simpler way that only gcc understands but
take care to not use gccisms when and if I patch build bits.

- Arnaldo

Re: [PATCH][RFC] PentiumPro/II split in x86 config

[J.A. Magallon]

On 2002.05.28 Arnaldo Carvalho de Melo wrote:
>Em Tue, May 28, 2002 at 11:55:47AM +0900, Miles Bader escreveu:
>> Keith Owens <kaos@ocs.com.au> writes:
>> > The kernel can only be compiled with gcc, but some bits of the build
>> > are compiled and run on the host, using the host compiler.  Avoid using
>> > gccisms where there is a standard way of doing it.
>> 
>> That particular gccism completely infests the kernel, so there seems
>> little point in avoiding it in favor of the uglier standard syntax.
>
>Agreed.
>
>What I'll do: continue using the simpler way that only gcc understands but
>take care to not use gccisms when and if I patch build bits.
>

Problem is that named initializers '.xx =' are ISO C99, so problably they
are not supported in gcc till 3.0...the old way is working with older
compilers.

-- 
J.A. Magallon                           #  Let the source be with you...        
mailto:jamagallon@able.es
Mandrake Linux release 8.3 (Cooker) for i586
Linux werewolf 2.4.19-pre8-jam4 #2 SMP dom may 26 11:20:42 CEST 2002 i686

Re: [PATCH][RFC] PentiumPro/II split in x86 config

[Mikael Pettersson]

J.A. Magallon writes:
 > Problem is that named initializers '.xx =' are ISO C99, so problably they
 > are not supported in gcc till 3.0...the old way is working with older
 > compilers.

"probably"? Why not check the facts. 2.95.3 implements ".name ="
initialisers, and 2.95.3 is also listed in 2.4.18's Documentation/Changes
as the oldest acceptable compiler.

I agree with Keith that we really should prefer standard C solutions
over gcc-specific hacks _when_they_exist_.

Also note that gcc is no longer the only compiler able to compile the
kernel. Intel claims that their icc6 compiler has correctly compiled 2.4.18
with only minor tweaks needed. They do implement inline asm() nowadays, but
alas not &&label and computed gotos.

/Mikael

Re: [PATCH][RFC] PentiumPro/II split in x86 config

[David Woodhouse]

mikpe@csd.uu.se said:
>  They do implement inline asm() nowadays, but alas not &&label and
> computed gotos.

The only places I've seen &&label used are where it's been passed into an 
inline asm which has jumped to it... but gcc has optimised the label and 
the code following it away because it was never used (inline asm isn't 
allowed to do that).

--
dwmw2

Re: [PATCH][RFC] PentiumPro/II split in x86 config

[Albert D. Cahalan]

David Woodhouse writes:
> mikpe@csd.uu.se said:

>> They do implement inline asm() nowadays, but alas not &&label and
>> computed gotos.
>
> The only places I've seen &&label used


In the kernel or elsewhere? It's certainly useful.
Here it's used to make up for 'case' not supporting
strings, avoiding a cascade of 'else if'.


///////////////////////////////////////////////////////////////////////

static const char *set_personality(void){
  char *s;
  size_t sl;
  char buf[16];
  personality_table_struct findme = { buf, NULL};
  personality_table_struct *found;
  static const personality_table_struct personality_table[] = {
  {"390",      &&case_390},
  {"aix",      &&case_aix},
  {"gnu",      &&case_gnu},
  {"hp",       &&case_hp},
  {"hpux",     &&case_hpux},
  {"irix",     &&case_irix},
  {"os390",    &&case_os390},
  {"s390",     &&case_s390},
  {"sco",      &&case_sco},
  {"sgi",      &&case_sgi},
  {"unknown",  &&case_unknown}
  };
  const int personality_table_count
    = sizeof(personality_table)/sizeof(personality_table_struct);

  personality = 0;
  s = getenv("CMD_ENV");
  if(!s || !*s) s="unknown";   /* "Do The Right Thing[tm]" */
  sl = strlen(s);
  if(sl > 15) return "Environment specified an unknown personality.";
  strncpy(buf, s, sl);
  buf[sl] = '\0';
  saved_personality_text = strdup(buf);

  found = bsearch(&findme, personality_table, personality_table_count,
      sizeof(personality_table_struct), compare_personality_table_structs
  );

  if(!found) return "Environment specified an unknown personality.";

  goto *(found->jump);    /* See gcc extension info.  :-)   */

  case_gnu:
    personality = PER_GOOD_o | PER_CUMUL_MARKED | PER_OLD_m;
    // other stuff...
    return NULL;

  case_unknown: /* defaults, but also check inferior environment variables */
    if(
      getenv("UNIX95")     /* Irix */
      || getenv("POSIXLY_CORRECT")  /* most gnu stuff */
      || (getenv("POSIX2") && !strcmp(getenv("POSIX2"), "on")) /* Unixware 7 */
    ) personality = PER_BROKEN_o;
    return NULL;

  case_aix:
     // blah, blah...
     return NULL;

  case_irix:
  case_sgi:
    s = getenv("_XPG");
    if(s && s[0]>'0' && s[0]<='9') personality = PER_BROKEN_o;
    else personality = PER_IRIX_l;
    return NULL;

  case_os390:  /* IBM's OS/390 OpenEdition on the S/390 mainframe */
  case_s390:
  case_390:
    personality = PER_390_j;
    return NULL;

  case_hp:
  case_hpux:
  case_sco:
    personality = PER_BROKEN_o;
    return NULL;
}


//////////////////////////////////////////////////////////////////

Re: [PATCH][RFC] PentiumPro/II split in x86 config

[Miles Bader]

Mikael Pettersson <mikpe@csd.uu.se> writes:
> I agree with Keith that we really should prefer standard C solutions
> over gcc-specific hacks _when_they_exist_.

Since portability to other compilers is really not an option with linux,
it's a lot more important that the kernel code use a _consistent_
convention than it use a `standard' one.

So before recommending that people use a different syntax than the one
historically used, are you going to run over the whole kernel and
replace all the existing uses of `field:' with `.field = ' (and brave
the flamewar that it would probably require)?

-Miles
-- 
Suburbia: where they tear out the trees and then name streets after them.

Re: [PATCH][RFC] PentiumPro/II split in x86 config

[Roland Dreier]

>>>>> "J" == J A Magallon <J.A.> writes:

    J> Problem is that named initializers '.xx =' are ISO C99, so
    J> problably they are not supported in gcc till 3.0...the old way
    J> is working with older compilers.

I actually tried it :).  gcc 2.95 supports named initializers as well:

$ cat a.c
struct foo {
  int x;
  int y;
};

struct foo bar = {
  .y = 2,
  .x = 1
};

int main() {
  printf("%d\n", bar.x);
  return 0;
}

$ gcc a.c
$ ./a.out
1
$ gcc --version
2.95.2

Best,
 Roland

Re: [PATCH][RFC] PentiumPro/II split in x86 config

[Rusty Russell]

On Tue, 28 May 2002 00:02:00 -0300
Arnaldo Carvalho de Melo <acme@conectiva.com.br> wrote:

> Em Tue, May 28, 2002 at 11:55:47AM +0900, Miles Bader escreveu:
> > Keith Owens <kaos@ocs.com.au> writes:
> > > The kernel can only be compiled with gcc, but some bits of the build
> > > are compiled and run on the host, using the host compiler.  Avoid using
> > > gccisms where there is a standard way of doing it.
> > 
> > That particular gccism completely infests the kernel, so there seems
> > little point in avoiding it in favor of the uglier standard syntax.
> 
> Agreed.
> 
> What I'll do: continue using the simpler way that only gcc understands but
> take care to not use gccisms when and if I patch build bits.

WARNING: The older form is deprecated.  From the info pages:

	Another syntax which has the same meaning, obsolete since GCC 2.5, is
`FIELDNAME:', as shown here:

Janitors wanted,
Rusty.
-- 
   there are those who do and those who hang on and you don't see too
   many doers quoting their contemporaries.  -- Larry McVoy

Re: [PATCH][RFC] PentiumPro/II split in x86 config

[Arnaldo Carvalho de Melo]

Em Wed, May 29, 2002 at 02:23:50PM +1000, Rusty Russell escreveu:
> On Tue, 28 May 2002 00:02:00 -0300
> Arnaldo Carvalho de Melo <acme@conectiva.com.br> wrote:
> 
> > Em Tue, May 28, 2002 at 11:55:47AM +0900, Miles Bader escreveu:
> > > Keith Owens <kaos@ocs.com.au> writes:
> > > > The kernel can only be compiled with gcc, but some bits of the build
> > > > are compiled and run on the host, using the host compiler.  Avoid using
> > > > gccisms where there is a standard way of doing it.
> > > 
> > > That particular gccism completely infests the kernel, so there seems
> > > little point in avoiding it in favor of the uglier standard syntax.
> > 
> > Agreed.
> > 
> > What I'll do: continue using the simpler way that only gcc understands but
> > take care to not use gccisms when and if I patch build bits.
> 
> WARNING: The older form is deprecated.  From the info pages:
> 
> 	Another syntax which has the same meaning, obsolete since GCC 2.5, is
> `FIELDNAME:', as shown here:
> 
> Janitors wanted,

Ouch, Rusty, I'll reread the info pages and go over all the tree and start
submitting patches, starting tomorrow. Expect that sound, multiple times.

Powers that be: holler now or...

- Arnaldo

Re: [PATCH][RFC] PentiumPro/II split in x86 config

[Dave Jones]

On Mon, May 27, 2002 at 10:29:25PM -0300, Arnaldo Carvalho de Melo wrote:
 > 	Since you're working on this could I suggest that you use labeled
 > elements, this gccism make the initialization above way more cleaner, safer and
 > easy to read :-) This is being used in the kernel in places like the FSes, the
 > TCP/IP stack and lots of other places.

Patrick Mochel already did it in his reworking of the arch/i386/kernel cruft
It's already merged in my tree, and will hopefully turn up in Linus' tree
sometime soon. So far, it's been dropped (probably because it rejected
when someone else touched something there)

I'll push the resynced version later today

    Dave.

-- 
| Dave Jones.        http://www.codemonkey.org.uk
| SuSE Labs

Re: [PATCH][RFC] PentiumPro/II split in x86 config

[Keith Owens]

On Mon, 27 May 2002 16:54:20 +0200, 
"J.A. Magallon" <jamagallon@able.es> wrote:
>Due to Alan's advice, it also adds a check that will panic if a PII or
>higher kernel is run on a PPro or lesser (plz, I put that code in the
>place I thought it was the best, but probably I'm wrong...).
>+static void __init check_intel_compat(struct cpuinfo_x86 *c)
>+{
>+#if defined(CONFIG_MPENTIUMII) || defined(CONFIG_MPENTIUMIII) || defined(CONFIG_MPENTIUM4)
>+	if (c->x86 <= 5)
>+		panic("Kernel is unsafe/incompatible with this CPU model. Check your build settings !\n");
>+#endif
>+}

Don't rely on that working.  When you compile with -march=i686, gcc
emits cmov instructions all over the place, including in printk code.
The first cmov takes a fault and tries to panic, the panic code uses
printk which hits a second cmov and the machine is dead with no
messages.