Very Computer

Currently sys_set_thread_area has a magic flags argument that might
change it's behaivour completly.

Split out the TLS_FLAG_CLEAR case that has nothing in common with the
rest into it's own syscall, sys_clear_thread_area and change the
second argument to int writable.

--- 1.39/arch/i386/kernel/entry.S       Tue Jul 30 00:08:08 2002

        .long sys_sched_setaffinity
        .long sys_sched_getaffinity
        .long sys_set_thread_area
+       .long sys_clear_thread_area

        .rept NR_syscalls-(.-sys_call_table)/4
                .long sys_ni_syscall
--- 1.29/arch/i386/kernel/process.c     Mon Jul 29 04:07:12 2002

 /*
  * Set the Thread-Local Storage area:
  */
-asmlinkage int sys_set_thread_area(unsigned long base, unsigned long flags)
+asmlinkage int sys_set_thread_area(unsigned long base, int writable)
 {
        struct thread_struct *t = &current->thread;
-       int writable = 0;
-       int cpu;
+       int cpu = get_cpu();

-       /* do not allow unused flags */
-       if (flags & ~TLS_FLAGS_MASK)
-               return -EINVAL;
-
-       /*
-        * Clear the TLS?
-        */
-       if (flags & TLS_FLAG_CLEAR) {
-               cpu = get_cpu();
-               t->tls_desc.a = t->tls_desc.b = 0;
-               load_TLS_desc(t, cpu);
-               put_cpu();
-               return 0;
-       }
-
-       if (flags & TLS_FLAG_WRITABLE)
-               writable = 1;
-
-       /*
-        * We must not get preempted while modifying the TLS.
-        */
-       cpu = get_cpu();
+       writable = !!writable; /* must be one or zero */

-        t->tls_desc.a = ((base & 0x0000ffff) << 16) | 0xffff;
-
-        t->tls_desc.b = (base & 0xff000000) | ((base & 0x00ff0000) >> 16) |
+       t->tls_desc.a = ((base & 0x0000ffff) << 16) | 0xffff;
+       t->tls_desc.b = (base & 0xff000000) | ((base & 0x00ff0000) >> 16) |
                                0xf0000 | (writable << 9) | (1 << 15) |
                                        (1 << 22) | (1 << 23) | 0x7000;

        return TLS_ENTRY*8 + 3;
 }

+
+/*
+ * Clear the Thread-Local Storage area:
+ */
+asmlinkage void sys_clear_thread_area(void)
+{
+       struct thread_struct *t = &current->thread;
+       int cpu = get_cpu();
+
+       t->tls_desc.a = t->tls_desc.b = 0;
+       load_TLS_desc(t, cpu);
+
+       put_cpu();
+}
--- 1.7/include/asm-i386/desc.h Mon Jul 29 04:07:52 2002

        _set_tssldt_desc(&cpu_gdt_table[cpu][LDT_ENTRY], (int)addr, ((size << 3)-1), 0x82);
 }

-#define TLS_FLAGS_MASK                 0x00000003
-
-#define TLS_FLAG_WRITABLE              0x00000001
-#define TLS_FLAG_CLEAR                 0x00000002
-
 static inline void load_TLS_desc(struct thread_struct *t, unsigned int cpu)
 {
        cpu_gdt_table[cpu][TLS_ENTRY] = t->tls_desc;
--- 1.11/include/asm-i386/unistd.h      Tue Jul 30 00:08:09 2002

 #define __NR_futex             240
 #define __NR_sched_setaffinity 241
 #define __NR_sched_getaffinity 242
+#define __NR_set_thread_area   243
+#define __NR_clear_thread_area 244

 /* user-visible error numbers are in the range -1 - -124: see <asm-i386/errno.h> */

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in

More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

i did not feel like wasting two syscall slots for this, but the cleanups
look fine to me otherwise.

        Ingo

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in

More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Actually, is the clear operation really necessary?
IMHO the best clear is movw $0x03, %gs, then all accesses through %gs will
trap. Calling set_thread_area (0, 1); will result in 0xb segment
acting exactly like %ds or %es.

        Jakub
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in

More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

indeed. I've attached a (tested) patch against BK-curr that removes just
the clear operation. I've left the flags mask and the writable flag just
so that we have the option to introduce extensions without breaking the
ABI.

        Ingo

--- linux/arch/i386/kernel/process.c.orig       Tue Jul 30 22:13:43 2002

        if (flags & ~TLS_FLAGS_MASK)
                return -EINVAL;

-       /*
-        * Clear the TLS?
-        */
-       if (flags & TLS_FLAG_CLEAR) {
-               cpu = get_cpu();
-               t->tls_desc.a = t->tls_desc.b = 0;
-               load_TLS_desc(t, cpu);
-               put_cpu();
-               return 0;
-       }
-
        if (flags & TLS_FLAG_WRITABLE)
                writable = 1;

--- linux/include/asm-i386/desc.h.orig  Tue Jul 30 22:14:10 2002

        _set_tssldt_desc(&cpu_gdt_table[cpu][LDT_ENTRY], (int)addr, ((size << 3)-1), 0x82);
 }

-#define TLS_FLAGS_MASK                 0x00000003
+#define TLS_FLAGS_MASK                 0x00000001

 #define TLS_FLAG_WRITABLE              0x00000001
-#define TLS_FLAG_CLEAR                 0x00000002

 static inline void load_TLS_desc(struct thread_struct *t, unsigned int cpu)
 {
--- linux/include/asm-i386/unistd.h.orig        Tue Jul 30 22:14:40 2002

 #define __NR_futex             240
 #define __NR_sched_setaffinity 241
 #define __NR_sched_getaffinity 242
+#define __NR_set_thread_area   243

 /* user-visible error numbers are in the range -1 - -124: see <asm-i386/errno.h> */

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in

More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

At least on x86-64 it is useful to have a clear operation, because setting the
thread descriptors adds some cost to the context switch for various reasons.
This way processes you could disable it again when they don't need it anymore.

-Andi
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in

More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/