Because limit gives the address of the last addressable

byte in the segment, the limit argument to SEG16 and SEG needs to have 1 subtracted from it.

Because limit gives the address of the last addressable
2ef3a64b · rsc · 64659055 · 2ef3a64b
--- a/proc.c
+++ b/proc.c
@@ -38,13 +38,13 @@ setupsegs(struct proc *p)
  }

  c->gdt[0] = SEG_NULL;
-  c->gdt[SEG_KCODE] = SEG(STA_X|STA_R, 0, 0x100000 + 64*1024, 0);
+  c->gdt[SEG_KCODE] = SEG(STA_X|STA_R, 0, 0x100000 + 64*1024-1, 0);
  c->gdt[SEG_KDATA] = SEG(STA_W, 0, 0xffffffff, 0);
-  c->gdt[SEG_TSS] = SEG16(STS_T32A, (uint) &c->ts, sizeof(c->ts), 0);
+  c->gdt[SEG_TSS] = SEG16(STS_T32A, (uint)&c->ts, sizeof(c->ts)-1, 0);
  c->gdt[SEG_TSS].s = 0;
  if(p){
-    c->gdt[SEG_UCODE] = SEG(STA_X|STA_R, (uint)p->mem, p->sz, DPL_USER);
-    c->gdt[SEG_UDATA] = SEG(STA_W, (uint)p->mem, p->sz, DPL_USER);
+    c->gdt[SEG_UCODE] = SEG(STA_X|STA_R, (uint)p->mem, p->sz-1, DPL_USER);
+    c->gdt[SEG_UDATA] = SEG(STA_W, (uint)p->mem, p->sz-1, DPL_USER);
  } else {
    c->gdt[SEG_UCODE] = SEG_NULL;
    c->gdt[SEG_UDATA] = SEG_NULL;