xnu-1228.5.18.tar.gz

[apple/xnu.git] / osfmk / i386 / locore.s

diff --git a/osfmk/i386/locore.s b/osfmk/i386/locore.s
index 29e35692299bf0bffee0111899248507a5981dec..ac1bb007a7a44a711303f18311f692432b69b032 100644 (file)
--- a/osfmk/i386/locore.s
+++ b/osfmk/i386/locore.s
@@ -226,30 +226,35 @@ Entry(timer_grab)
  * Nanotime returned in %edx:%eax.
  * Computed from tsc based on the scale factor
  * and an implicit 32 bit shift.
+ * This code must match what _rtc_nanotime_read does in
+ * i386/machine_routines_asm.s.  Failure to do so can
+ * result in "weird" timing results.
  *
  * Uses %eax, %ebx, %ecx, %edx, %esi, %edi.
  */
 #define RNT_INFO               _rtc_nanotime_info
-#define NANOTIME                                                                                                                 \
-0:     movl    RNT_INFO+RNT_TSC_BASE,%esi                                                                      ; \
-       movl    RNT_INFO+RNT_TSC_BASE+4,%edi                                                            ; \
-       rdtsc                                                                                                                           ; \
-       subl    %esi,%eax                                               /* tsc - tsc_base */            ; \
-       sbbl    %edi,%edx                                                                                                       ; \
-       movl    RNT_INFO+RNT_SCALE,%ecx                                                                         ; \
-       movl    %edx,%ebx                                               /* delta * scale */                     ; \
-       mull    %ecx                                                                                                            ; \
-       movl    %ebx,%eax                                                                                                       ; \
-       movl    %edx,%ebx                                                                                                       ; \
-       mull    %ecx                                                                                                            ; \
-       addl    %ebx,%eax                                                                                                       ; \
-       adcl    $0,%edx                                                 /* add carry into hi */         ; \
-       addl    RNT_INFO+RNT_NS_BASE,%eax               /* add ns_base lo */            ; \
-       adcl    RNT_INFO+RNT_NS_BASE+4,%edx             /* add ns_base hi */            ; \
-       cmpl    RNT_INFO+RNT_TSC_BASE,%esi                                                                      ; \
-       jne     0b                                                                      /* repeat if changed */         ; \
-       cmpl    RNT_INFO+RNT_TSC_BASE+4,%edi                                                            ; \
-       jne     0b
+#define NANOTIME                                                       \
+       lea     RNT_INFO,%edi                                           ; \
+0:                                                                     ; \
+       movl    RNT_GENERATION(%edi),%esi       /* being updated? */    ; \
+       testl   %esi,%esi                                               ; \
+       jz      0b                              /* wait until done */   ; \
+       rdtsc                                                           ; \
+       subl    RNT_TSC_BASE(%edi),%eax                                 ; \
+       sbbl    RNT_TSC_BASE+4(%edi),%edx       /* tsc - tsc_base */    ; \
+       movl    RNT_SCALE(%edi),%ecx            /* * scale factor */    ; \
+       movl    %edx,%ebx                                               ; \
+       mull    %ecx                                                    ; \
+       movl    %ebx,%eax                                               ; \
+       movl    %edx,%ebx                                               ; \
+       mull    %ecx                                                    ; \
+       addl    %ebx,%eax                                               ; \
+       adcl    $0,%edx                                                 ; \
+       addl    RNT_NS_BASE(%edi),%eax          /* + ns_base */         ; \
+       adcl    RNT_NS_BASE+4(%edi),%edx                                ; \
+       cmpl    RNT_GENERATION(%edi),%esi       /* check for update */  ; \
+       jne     0b                              /* do it all again */
+
 
 /*
  * Add 64-bit delta in register dreg : areg to timer pointed to by register treg.