[src/trunk]: src/sys/arch/amd64/amd64 clarify

[maxv <maxv%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/949057a05a9f
branches:  trunk
changeset: 345096:949057a05a9f
user:      maxv <maxv%NetBSD.org@localhost>
date:      Sat May 07 13:08:30 2016 +0000

description:
clarify

diffstat:

 sys/arch/amd64/amd64/mptramp.S |  69 +++++++++++++++++++++++------------------
 1 files changed, 39 insertions(+), 30 deletions(-)

diffs (158 lines):

diff -r 3d324bd7eb23 -r 949057a05a9f sys/arch/amd64/amd64/mptramp.S
--- a/sys/arch/amd64/amd64/mptramp.S    Sat May 07 12:45:55 2016 +0000
+++ b/sys/arch/amd64/amd64/mptramp.S    Sat May 07 13:08:30 2016 +0000
@@ -1,13 +1,11 @@
-/*     $NetBSD: mptramp.S,v 1.19 2015/12/09 16:55:18 maxv Exp $        */
+/*     $NetBSD: mptramp.S,v 1.20 2016/05/07 13:08:30 maxv Exp $        */
 
 /*-
- * Copyright (c) 2000 The NetBSD Foundation, Inc.
+ * Copyright (c) 2000, 2016 The NetBSD Foundation, Inc.
  * All rights reserved.
  *
  * This code is derived from software contributed to The NetBSD Foundation
- * by RedBack Networks Inc.
- *
- * Author: Bill Sommerfeld
+ * by RedBack Networks Inc. (Author: Bill Sommerfeld), and Maxime Villard.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -30,7 +28,7 @@
  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  * POSSIBILITY OF SUCH DAMAGE.
  */
-       
+
 /*
  * Copyright (c) 1999 Stefan Grefen
  *
@@ -62,10 +60,11 @@
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  */
+
 /*
  * MP startup ...
- * the stuff from cpu_spinup_trampoline to mp_startup 
- * is copied into the first 640 KB
+ * the stuff from cpu_spinup_trampoline to mp_startup is copied into the
+ * first 640 KB.
  *
  * We startup the processors now when the kthreads become ready.
  * The steps are:
@@ -74,9 +73,9 @@
  *     2) halt the processors waiting for them to be enabled
  *        by a idle-thread 
  */
-       
+
 #include "opt_mpbios.h"                /* for MPDEBUG */
-               
+
 #include "assym.h"
 #include <machine/asm.h>
 #include <machine/specialreg.h>
@@ -91,22 +90,27 @@
 #define _TRMP_LABEL(a)  a = . - _C_LABEL(cpu_spinup_trampoline) + MP_TRAMPOLINE
 
 #ifdef MPDEBUG
-
 /*
  * Debug code to stop aux. processors in various stages based on the
  * value in cpu_trace.
  *
- * %edi points at cpu_trace;  cpu_trace[0] is the "hold point";
- * cpu_trace[1] is the point which the CPU has reached.
+ * %edi points at cpu_trace;
+ * cpu_trace[0] is the "hold point";
+ * cpu_trace[1] is the point which the CPU has reached;
  * cpu_trace[2] is the last value stored by HALTT.
  */
-
-#define HALT(x)        1: movl (%edi),%ebx;cmpl $ x,%ebx ; jle 1b ; movl $x,4(%edi)
-#define HALTT(x,y)     movl y,8(%edi); HALT(x)
+#define HALT(x) \
+1:     movl (%edi),%ebx        ;       \
+       cmpl $x,%ebx            ;       \
+       jle 1b                  ;       \
+       movl $x,4(%edi)         ;
+#define HALTT(x,y) \
+       movl y,8(%edi)          ;       \
+       HALT(x)                 ;
 #else
-#define HALT(x)        /**/
-#define HALTT(x,y) /**/
-#endif
+#define HALT(x)
+#define HALTT(x,y)
+#endif /* MPDEBUG */
 
        .global _C_LABEL(cpu_spinup_trampoline)
        .global _C_LABEL(cpu_spinup_trampoline_end)
@@ -156,13 +160,14 @@
        pushl   $PSL_MBO
        popfl
 
+       /* Enable PAE, SSE, and PSE if available */
        movl    %cr4,%eax
        orl     $(CR4_PAE|CR4_OSFXSR|CR4_OSXMMEXCPT),%eax
        movl    RELOC(pmap_largepages),%ecx
        orl     %ecx,%ecx
-       jz      1f
+       jz      no_PSE
        orl     $CR4_PSE,%eax
-1:
+no_PSE:
        movl    %eax,%cr4
 
        movl    $MSR_EFER,%ecx
@@ -171,12 +176,15 @@
        orl     $(EFER_LME|EFER_SCE),%eax
        wrmsr
 
+       /* Load %cr3. */
        movl    RELOC(mp_pdirpa),%ecx   /* guaranteed < 4G */
-       movl    %ecx,%cr3               /* load ptd addr into mmu */
+       movl    %ecx,%cr3               /* load PTD addr into MMU */
 
-       movl    %cr0,%eax               /* get control word */
+       /* Enable paging and the rest of it. */
+       movl    %cr0,%eax
        orl     $(CR0_PE|CR0_PG|CR0_NE|CR0_TS|CR0_MP|CR0_WP|CR0_AM),%eax
        movl    %eax,%cr0
+
        jmp     mptramp_compat
 mptramp_compat:
 
@@ -194,22 +202,23 @@
        .long   mptramp_longmode
        .word   GSEL(GCODE_SEL, SEL_KPL)
 
+#define GDT_LIMIT      0x17    /* 23 = 3 * 8 - 1 */
 _TRMP_LABEL(mptramp_gdt32)
        .quad 0x0000000000000000
-       .quad 0x00cf9f000000ffff
-       .quad 0x00cf93000000ffff
+       .quad 0x00cf9f000000ffff        /* CS */
+       .quad 0x00cf93000000ffff        /* DS */
 _TRMP_LABEL(mptramp_gdt32_desc)
-       .word 0x17
+       .word GDT_LIMIT
        .long mptramp_gdt32
 
 _TRMP_LABEL(mptramp_gdt64)
        .quad 0x0000000000000000
-       .quad 0x00af9a000000ffff
-       .quad 0x00cf92000000ffff
+       .quad 0x00af9a000000ffff        /* CS */
+       .quad 0x00cf92000000ffff        /* DS */
 _TRMP_LABEL(mptramp_gdt64_desc)
-       .word 0x17
+       .word GDT_LIMIT
        .long mptramp_gdt64
-
+#undef GDT_LIMIT
 
 _TRMP_LABEL(mptramp_longmode)
        .code64