2006-11-05 Barry deFreese <bddebian@comcast.net>

[task #5878 --- ``Backport code from GNU Mach's trunk to
	gnumach-1-branch: i386_set_gdt, i386_get_gdt'']

	* i386/include/mach/i386/mach_i386.defs (i386_set_gdt, i386_get_gdt):
	New routines.
	* i386/i386/user_ldt.c (i386_set_gdt, i386_get_gdt): New functions.
	* i386/i386/gdt.h (USER_GDT, USER_GDT_SLOTS): New macros.
	(GDTSZ): Compute it from USER_GDT and USER_GDT_SLOTS.
	* i386/i386/thread.h: Include `gdt.h'.
	(struct i386_machine_state): New member `user_gdt'.
	* i386/i386/pcb.c (switch_ktss): Copy those slots into the GDT.
	* linux/dev/include/linux/head.h: New file.

5 files changed, 82 insertions, 1 deletions

diff --git a/i386/i386/gdt.h b/i386/i386/gdt.h
index 49cb0d3..4715759 100644
--- a/i386/i386/gdt.h
+++ b/i386/i386/gdt.h
@@ -49,8 +49,10 @@
 #define	USER_FPREGS	0x40		/* user-mode access to saved
 					   floating-point registers */
 
-#define	GDTSZ		11
+#define	USER_GDT	0x48		/* user-defined GDT entries */
+#define	USER_GDT_SLOTS	2
 
+#define	GDTSZ		(USER_GDT/8 + USER_GDT_SLOTS)
 
 extern struct real_descriptor gdt[GDTSZ];
 
diff --git a/i386/i386/pcb.c b/i386/i386/pcb.c
index 9665caa..a18a5e6 100644
--- a/i386/i386/pcb.c
+++ b/i386/i386/pcb.c
@@ -191,6 +191,13 @@ void switch_ktss(pcb)
 	    set_ldt(USER_LDT);
 	}
     }
+
+    /* Copy in the per-thread GDT slots.  No reloading is necessary
+       because just restoring the segment registers on the way back to
+       user mode reloads the shadow registers from the in-memory GDT.  */
+    memcpy (gdt_desc_p (mycpu, USER_GDT),
+        pcb->ims.user_gdt, sizeof pcb->ims.user_gdt);
+
 	/*
 	 * Load the floating-point context, if necessary.
 	 */
diff --git a/i386/i386/thread.h b/i386/i386/thread.h
index 027193a..337190e 100644
--- a/i386/i386/thread.h
+++ b/i386/i386/thread.h
@@ -41,6 +41,7 @@
 
 #include <i386/iopb.h>
 #include <i386/tss.h>
+#include "gdt.h"
 
 /*
  *	i386_saved_state:
@@ -161,6 +162,7 @@ struct i386_machine_state {
 	struct user_ldt	*	ldt;
 	struct i386_fpsave_state *ifps;
 	struct v86_assist_state	v86s;
+	struct real_descriptor user_gdt[USER_GDT_SLOTS];
 };
 
 typedef struct pcb {
diff --git a/i386/i386/user_ldt.c b/i386/i386/user_ldt.c
index 33724ec..3f37599 100644
--- a/i386/i386/user_ldt.c
+++ b/i386/i386/user_ldt.c
@@ -401,3 +401,57 @@ user_ldt_free(user_ldt)
 		user_ldt->desc.limit_low + 1
 		+ sizeof(struct real_descriptor));
 }
+
+
+kern_return_t
+i386_set_gdt (thread_t thread, int *selector, struct real_descriptor desc)
+{
+  int idx;
+
+  if (thread == THREAD_NULL)
+    return KERN_INVALID_ARGUMENT;
+
+  if (*selector == -1)
+    {
+      for (idx = 0; idx < USER_GDT_SLOTS; ++idx)
+        if ((thread->pcb->ims.user_gdt[idx].access & ACC_P) == 0)
+          {
+            *selector = ((idx + sel_idx(USER_GDT)) << 3) | SEL_PL_U;
+            break;
+          }
+      if (idx == USER_GDT_SLOTS)
+        return KERN_NO_SPACE;   /* ? */
+    }
+  else if ((*selector & (SEL_LDT|SEL_PL)) != SEL_PL_U
+           || sel_idx (*selector) < sel_idx(USER_GDT)
+           || sel_idx (*selector) >= sel_idx(USER_GDT) + USER_GDT_SLOTS)
+    return KERN_INVALID_ARGUMENT;
+  else
+    idx = sel_idx (*selector) - sel_idx(USER_GDT);
+
+  if ((desc.access & ACC_P) == 0)
+    memset (&thread->pcb->ims.user_gdt[idx], 0,
+            sizeof thread->pcb->ims.user_gdt[idx]);
+  else if ((desc.access & (ACC_TYPE_USER|ACC_PL)) != (ACC_TYPE_USER|ACC_PL_U))
+    return KERN_INVALID_ARGUMENT;
+  else
+    thread->pcb->ims.user_gdt[idx] = desc;
+
+  return KERN_SUCCESS;
+}
+
+kern_return_t
+i386_get_gdt (thread_t thread, int selector, struct real_descriptor *desc)
+{
+  if (thread == THREAD_NULL)
+    return KERN_INVALID_ARGUMENT;
+
+  if ((selector & (SEL_LDT|SEL_PL)) != SEL_PL_U
+      || sel_idx (selector) < sel_idx(USER_GDT)
+      || sel_idx (selector) >= sel_idx(USER_GDT) + USER_GDT_SLOTS)
+    return KERN_INVALID_ARGUMENT;
+
+  *desc = thread->pcb->ims.user_gdt[sel_idx (selector) - sel_idx(USER_GDT)];
+
+  return KERN_SUCCESS;
+}
diff --git a/i386/include/mach/i386/mach_i386.defs b/i386/include/mach/i386/mach_i386.defs
index 55121b6..1f98dc3 100644
--- a/i386/include/mach/i386/mach_i386.defs
+++ b/i386/include/mach/i386/mach_i386.defs
@@ -66,3 +66,19 @@ routine	i386_get_ldt(
 		first_selector	: int;
 		selector_count	: int;
 	out	desc_list	: descriptor_list_t);
+
+/* Modify one of a few available thread-specific segment descriptor slots.
+   The SELECTOR must be a value from a previous call (on any thread),
+   or -1 to allocate an available slot and return the segment selector for it.
+   These slots are copied into the CPU on each thread switch.
+   Returns KERN_NO_SPACE when there are no more slots available.  */
+routine i386_set_gdt(
+                target_thread   : thread_t;
+        inout   selector        : int;
+                desc            : descriptor_t);
+
+/* Fetch a segment descriptor set with a prior i386_set_gdt call.  */
+routine i386_get_gdt(
+                target_thread   : thread_t;
+                selector        : int;
+        out     desc            : descriptor_t);