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Subject[patch] CLONE_SETTLS, CLONE_SETTID, 2.5.31-BK

okay, the attached patch gets rid of clone_startup() and adds two new
clone() flags instead:

CLONE_SETTLS => if present then the third clone() syscall parameter
is the new TLS.

CLONE_SETTID => if present then the child TID is written to the
address specified by the fourth clone() parameter.

the new parameters are handled in a safe way, clone() returns -EFAULT or
-EINVAL if there's some problem with them.

No current code is affected by these new flags. Patch was testbooted on
2.5.31-BK-current.

Ingo

--- linux/arch/i386/kernel/process.c.orig Tue Aug 13 20:10:25 2002
+++ linux/arch/i386/kernel/process.c Tue Aug 13 20:30:11 2002
@@ -559,6 +559,7 @@
unsigned long unused,
struct task_struct * p, struct pt_regs * regs)
{
+ struct thread_struct *t = &p->thread;
struct pt_regs * childregs;
struct task_struct *tsk;

@@ -567,17 +568,45 @@
childregs->eax = 0;
childregs->esp = esp;

- p->thread.esp = (unsigned long) childregs;
- p->thread.esp0 = (unsigned long) (childregs+1);
+ t->esp = (unsigned long) childregs;
+ t->esp0 = (unsigned long) (childregs+1);
+ t->eip = (unsigned long) ret_from_fork;

- p->thread.eip = (unsigned long) ret_from_fork;
-
- savesegment(fs,p->thread.fs);
- savesegment(gs,p->thread.gs);
+ savesegment(fs, t->fs);
+ savesegment(gs, t->gs);

tsk = current;
unlazy_fpu(tsk);
- struct_cpy(&p->thread.i387, &tsk->thread.i387);
+ struct_cpy(&t->i387, &tsk->thread.i387);
+
+ /*
+ * Set a new TLS for the child thread?
+ */
+ if (clone_flags & CLONE_SETTLS) {
+ struct desc_struct *desc;
+ struct user_desc info;
+ int idx;
+
+ if (copy_from_user(&info, (void *)childregs->esi, sizeof(info)))
+ return -EFAULT;
+ if (LDT_empty(&info))
+ return -EINVAL;
+
+ idx = info.entry_number;
+ if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
+ return -EINVAL;
+
+ desc = t->tls_array + idx - GDT_ENTRY_TLS_MIN;
+ desc->a = LDT_entry_a(&info);
+ desc->b = LDT_entry_b(&info);
+ }
+
+ /*
+ * Notify the child of the TID?
+ */
+ if (clone_flags & CLONE_SETTLS)
+ if (put_user(p->pid, (pid_t *)childregs->edx))
+ return -EFAULT;

if (unlikely(NULL != tsk->thread.ts_io_bitmap)) {
p->thread.ts_io_bitmap = kmalloc(IO_BITMAP_BYTES, GFP_KERNEL);
@@ -747,8 +776,7 @@
asmlinkage int sys_clone(struct pt_regs regs)
{
struct task_struct *p;
- unsigned long clone_flags;
- unsigned long newsp;
+ unsigned long clone_flags, newsp;

clone_flags = regs.ebx;
newsp = regs.ecx;
--- linux/include/linux/sched.h.orig Tue Aug 13 19:55:06 2002
+++ linux/include/linux/sched.h Tue Aug 13 20:27:23 2002
@@ -45,6 +45,8 @@
#define CLONE_THREAD 0x00010000 /* Same thread group? */
#define CLONE_NEWNS 0x00020000 /* New namespace group? */
#define CLONE_SYSVSEM 0x00040000 /* share system V SEM_UNDO semantics */
+#define CLONE_SETTLS 0x00080000 /* create a new TLS for the child */
+#define CLONE_SETTID 0x00100000 /* write the TID back to userspace */

#define CLONE_SIGNAL (CLONE_SIGHAND | CLONE_THREAD)

-
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