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SubjectRe: [PATCH] sanitize TLS API

On Tue, 30 Jul 2002, Jakub Jelinek wrote:

> 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.

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
+++ linux/arch/i386/kernel/process.c Tue Jul 30 22:13:52 2002
@@ -851,17 +851,6 @@
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
+++ linux/include/asm-i386/desc.h Tue Jul 30 22:14:27 2002
@@ -86,10 +86,9 @@
_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
+++ linux/include/asm-i386/unistd.h Tue Jul 30 22:15:05 2002
@@ -247,6 +247,7 @@
#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> */

-
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