GNU Mach cpu detection fix

[Guillem Jover]

Hi,

I've fixed and enabled the cpu detection code in the Debian package,
it works great. :>

There were two related problems. CPUID trashed EBX and ECX and those
registers were being used to save the stack pointer and the cpu
flags, so when returing the stack pointer was totally trashed and
the cpu put in a very messy state, triggering an insta-reboot due
to a triple fault (I assume).

The following patch fixes both and enables the ID flag for Cyrix
CPUs.


2004-11-22  Guillem Jover  <guillem@hadrons.org>

        * i386/i386/locore.S (discover_x86_cpu_type): Enable function.
        Enable ID flag for Cyrix CPU. Use %ebp to save the stack pointer.
        Restore EFLAGS just after its last usage.
        * i386/i386at/model_dep.c (c_boot_entry): Enable use of
        discover_x86_cpu_type. Remove hardcoded cpu_type assignment.
        * i386/include/mach/i386/eflags.h
        (EFL_AC, EFL_VI, EFL_VIP, EFL_ID): New bits.


diff -Naur i386/i386/locore.S i386/i386/locore.S
--- i386/i386/locore.S  2001-10-07 21:47:15.000000000 +0200
+++ i386/i386/locore.S  2004-11-21 21:40:21.000000000 +0100
@@ -1144,13 +1144,16 @@
        jmp     _take_trap              /* treat as a trap */
 
 
-#if 0
 /* Discover what kind of cpu we have; return the family number
    (3, 4, 5, 6, for 386, 486, 586, 686 respectively).  */
 ENTRY(discover_x86_cpu_type)
-       movl    %esp,%edx               /* Save stack pointer */
+       pushl   %ebp                    /* Save frame pointer */
+       movl    %esp,%ebp               /* Save stack pointer */
        and     $~0x3,%esp              /* Align stack pointer */
 
+       inb     $0xe8,%al               /* Enable ID flag for Cyrix CPU ... */
+       andb    $0x80,%al               /* ... in CCR4 reg bit7 */
+       outb    %al,$0xe8
        pushfl                          /* Fetch flags ... */
        popl    %eax                    /*  ... into eax */
        movl    %eax,%ecx               /* Save original flags for return */
@@ -1159,6 +1162,8 @@
        popfl                           /*  ... In EFLAGS */
        pushfl                          /* Fetch flags back ... */
        popl    %eax                    /*  ... into eax */
+       pushl   %ecx                    /* From ecx... */
+       popfl                           /* ... restore original flags */
 
        xorl    %ecx,%eax               /* See if any bits didn't change */
        testl   $EFL_AC,%eax            /* Test AC bit */
@@ -1178,11 +1183,9 @@
        shrl    $8,%eax                 /* Slide family bits down */
        andl    $15,%eax                /* And select them */
 
-9:     pushl   %ecx                    /* From ecx... */
-       popfl                           /* ... restore original flags */
-       movl    %edx,%esp               /* Restore stack pointer */
+9:     movl    %ebp,%esp               /* Restore stack pointer */
+       popl    %ebp                    /* Restore frame pointer */
        ret                             /* And return */
-#endif
 
 
 /**/
diff -Naur i386/i386at/model_dep.c i386/i386at/model_dep.c
--- i386/i386at/model_dep.c     2002-05-23 03:54:57.000000000 +0200
+++ i386/i386at/model_dep.c     2004-11-21 21:41:09.000000000 +0100
@@ -372,7 +372,6 @@
        machine_slot[0].running = TRUE;
        machine_slot[0].cpu_subtype = CPU_SUBTYPE_AT386;
 
-#if 0
        switch (discover_x86_cpu_type ())
          {
          case 3:
@@ -389,10 +388,6 @@
            machine_slot[0].cpu_type = CPU_TYPE_PENTIUMPRO;
            break;
          }
-#else
-       machine_slot[0].cpu_type = CPU_TYPE_I386;
-#endif
-
 
        /*
         * Start the system.
diff -Naur i386/include/mach/i386/eflags.h i386/include/mach/i386/eflags.h
--- i386/include/mach/i386/eflags.h     2001-04-05 08:39:21.000000000 +0200
+++ i386/include/mach/i386/eflags.h     2004-11-21 21:39:13.000000000 +0100
@@ -45,5 +45,9 @@
 #define        EFL_NT          0x00004000              /* nested task */
 #define        EFL_RF          0x00010000              /* resume without 
tracing */
 #define        EFL_VM          0x00020000              /* virtual 8086 mode */
+#define        EFL_AC          0x00040000              /* alignment check */
+#define        EFL_VI          0x00080000              /* virtual interrupt */
+#define        EFL_VIP         0x00100000              /* virtual interrupt 
pending */
+#define        EFL_ID          0x00200000              /* cpuid available */
 
 #endif /* _MACH_I386_EFLAGS_H_ */