Changeset 11370

Timestamp:

Nov 16, 2008, 10:58:10 AM (11 years ago)

Author:

gb

Message:

Using i386_set_ldt() to point %fs at the tcr on 32-bit FreeBSD doesn't work
on a 64-bit kernel. Using i386_set_fsbase does work on both 32-bit and
64-bit kernels, but doesn't allow writing to %fs: at least by the time
we've called i386_set_fsbase() on thread startup, %fs contains an appropriate
selector and it never changes throughout the life of the thread.

Location:

trunk/source/lisp-kernel

Files:

• thread_manager.c (modified) (5 diffs)
• x86-spentry32.s (modified) (1 diff)
• x86-subprims32.s (modified) (1 diff)

trunk/source/lisp-kernel/thread_manager.c

@@ -1103 +1103 @@
 
 /* It'd be tempting to use i386_set_fsbase() here, but there doesn't
-   seem to be any way to free the GDT entry it creates. */
+   seem to be any way to free the GDT entry it creates.  Actually,
+   it's not clear that that really sets a GDT entry; let's see */
+
+#define FREEBSD_USE_SET_FSBASE 1
 void
 setup_tcr_extra_segment(TCR *tcr)
 {
+#if !FREEBSD_USE_SET_FSBASE
   struct segment_descriptor sd;
   uintptr_t addr = (uintptr_t)tcr;
@@ -1116 +1120 @@
   sd.sd_lobase = addr & ((1<<24)-1);
   sd.sd_hibase = (addr>>24)&0xff;
+
+
+
   sd.sd_type = 18;
   sd.sd_dpl = SEL_UPL;
@@ -1130 +1137 @@
     tcr->ldt_selector = LSEL(i,SEL_UPL);
   }
+#else
+  if (i386_set_fsbase((void*)tcr)) {
+    perror("i386_set_fsbase");
+    exit(1);
+  }
+  /* Once we've called i386_set_fsbase, we can't write to %fs. */
+  tcr->ldt_selector = GSEL(GUFS_SEL, SEL_UPL);
+#endif
 }
 
@@ -1135 +1150 @@
 free_tcr_extra_segment(TCR *tcr)
 {
+#if FREEBSD_USE_SET_FSBASE
+  /* On a 32-bit kernel, this allocates a GDT entry.  It's not clear
+     what it would mean to deallocate that entry. */
+  /* If we're running on a 64-bit kernel, we can't write to %fs */
+#else
   int idx = tcr->ldt_selector >> 3;
   /* load %fs with null segment selector */
@@ -1140 +1160 @@
   if (i386_set_ldt(idx, NULL, 1) < 0)
     perror("i386_set_ldt");
+#endif
   tcr->ldt_selector = 0;
 }
 #endif
+
 #ifdef SOLARIS
 #include <sys/sysi86.h>

trunk/source/lisp-kernel/x86-spentry32.s

@@ -4263 +4263 @@
         __(push %ebp)
         __(box_fixnum(%eax,%esi))       /* put callback index in arg_y */
-        __(ref_global(get_tcr,%eax))
-        __(subl $12,%esp)               /* alignment */
-        __(push $1)                     /* stack now 16-byte aligned */
-        __(call *%eax)
-        __(addl $16,%esp)               /* discard arg, alignment words */
-        /* linear TCR addr now in %eax */
-        __(movw tcr.ldt_selector(%eax), %rcontext_reg)
+        __ifndef([FREEBSD])
+         __(ref_global(get_tcr,%eax))
+         __(subl $12,%esp)              /* alignment */
+         __(push $1)                    /* stack now 16-byte aligned */
+         __(call *%eax)
+         __(addl $16,%esp)              /* discard arg, alignment words */
+         /* linear TCR addr now in %eax */
+         __(movw tcr.ldt_selector(%eax), %rcontext_reg)
+        __endif
 
         /* ebp is 16-byte aligned, and we've pushed 4 words.  Make

trunk/source/lisp-kernel/x86-subprims32.s

@@ -75 +75 @@
         __(push %ebx)
         __(mov 8(%ebp), %ebx)   /* get tcr */
-        __(movw tcr.ldt_selector(%ebx), %rcontext_reg)
+        __ifndef([FREEBSD])
+         __(movw tcr.ldt_selector(%ebx), %rcontext_reg)
+        __endif
         __(movl 8(%ebp),%eax)
         __(cmpl rcontext(tcr.linear),%eax)