clean up %fs %gs use

7b644318 · rsc · e97519a6 · 7b644318 · 7b644318 · 7b644318
--- a/bootasm.S
+++ b/bootasm.S
@@ -7,7 +7,6 @@

 #define SEG_KCODE 1  // kernel code
 #define SEG_KDATA 2  // kernel data+stack
-#define SEG_KCPU  3  // kernel per-cpu data

 #define CR0_PE    1  // protected mode enable bit

@@ -63,7 +62,7 @@ start32:
  movw    %ax, %ds                # -> DS: Data Segment
  movw    %ax, %es                # -> ES: Extra Segment
  movw    %ax, %ss                # -> SS: Stack Segment
-  movw    $(SEG_KCPU<<3), %ax     # Our per-cpu segment selector
+  movw    $0, %ax                 # Zero segments not ready for use
  movw    %ax, %fs                # -> FS
  movw    %ax, %gs                # -> GS


--- a/proc.c
+++ b/proc.c
@@ -93,9 +93,9 @@ ksegment(void)
  c1->gdt[SEG_UDATA] = SEG_NULL;
  c1->gdt[SEG_TSS] = SEG_NULL;
  lgdt(c1->gdt, sizeof(c1->gdt));
+  loadfsgs(SEG_KCPU << 3);
  
  // Initialize cpu-local variables.
-  setgs(SEG_KCPU << 3);
  c = c1;
  cp = 0;
 }

--- a/trapasm.S
+++ b/trapasm.S
@@ -13,10 +13,7 @@ alltraps:
  pushal
  
  # Set up data and per-cpu segments.
-  # Can find out KDATA from %ss.
-  # Assume that KCPU is KDATA+1.
  movw $(SEG_KDATA<<3), %ax
-  movw %ss, %ax
  movw %ax, %ds
  movw %ax, %es
  movw $(SEG_KCPU<<3), %ax

--- a/x86.h
+++ b/x86.h
@@ -104,9 +104,10 @@ xchg(volatile uint *addr, uint newval)
 }

 static inline void
-setgs(ushort gs)
+loadfsgs(ushort v)
 {
-  asm volatile("movw %0, %%gs" : : "r" (gs));
+  asm volatile("movw %0, %%fs" : : "r" (v));
+  asm volatile("movw %0, %%gs" : : "r" (v));
 }

 static inline void