But why not pass the child tidptr to ret_from_fork in a child register
rather than in a task_struct field?
The following patch implements this idea, but I only tested successful
compilation, not correct execution.
diff --exclude-from=/home/ldb/src/linux-exclude -urNdp linux-2.5.48_ldb_no_tid/arch/i386/kernel/entry.S linux-2.5.48_ldb/arch/i386/kernel/entry.S
--- linux-2.5.48_ldb_no_tid/arch/i386/kernel/entry.S 2002-11-18 15:30:37.000000000 +0100
+++ linux-2.5.48_ldb/arch/i386/kernel/entry.S 2002-11-20 21:18:49.000000000 +0100
@@ -192,7 +192,20 @@ ENTRY(lcall27)
jmp resume_userspace
+#define CLONE_CHILD_SETTID 0x01000000
ENTRY(ret_from_fork)
+ testl $CLONE_CHILD_SETTID, EBX(%esp)
+ je 2f
+ movl EDI(%esp), %ecx
+ movl EAX(%esp), %eax
+1: movl %eax, (%ecx)
+2:
+.section __ex_table,"a"
+ .align 4
+ .long 1b,2b
+.previous
+
+ movl $0, EAX(%esp)
#if CONFIG_SMP || CONFIG_PREEMPT
# NOTE: this function takes a parameter but it's unused on x86.
call schedule_tail
diff --exclude-from=/home/ldb/src/linux-exclude -urNdp linux-2.5.48_ldb_no_tid/arch/i386/kernel/process.c linux-2.5.48_ldb/arch/i386/kernel/process.c
--- linux-2.5.48_ldb_no_tid/arch/i386/kernel/process.c 2002-11-18 05:29:19.000000000 +0100
+++ linux-2.5.48_ldb/arch/i386/kernel/process.c 2002-11-20 15:26:24.000000000 +0100
@@ -225,7 +225,7 @@ int kernel_thread(int (*fn)(void *), voi
regs.eflags = 0x286;
/* Ok, create the new process.. */
- p = do_fork(flags | CLONE_VM | CLONE_UNTRACED, 0, ®s, 0, NULL);
+ p = do_fork(flags | CLONE_VM | CLONE_UNTRACED, 0, ®s, 0, NULL, NULL);
return IS_ERR(p) ? PTR_ERR(p) : p->pid;
}
@@ -285,9 +285,8 @@ int copy_thread(int nr, unsigned long cl
childregs = ((struct pt_regs *) (THREAD_SIZE + (unsigned long) p->thread_info)) - 1;
struct_cpy(childregs, regs);
- childregs->eax = 0;
+ childregs->eax = p->pid;
childregs->esp = esp;
- p->user_tid = NULL;
p->thread.esp = (unsigned long) childregs;
p->thread.esp0 = (unsigned long) (childregs+1);
@@ -502,7 +501,7 @@ asmlinkage int sys_fork(struct pt_regs r
{
struct task_struct *p;
- p = do_fork(SIGCHLD, regs.esp, ®s, 0, NULL);
+ p = do_fork(SIGCHLD, regs.esp, ®s, 0, NULL, NULL);
return IS_ERR(p) ? PTR_ERR(p) : p->pid;
}
@@ -511,14 +510,15 @@ asmlinkage int sys_clone(struct pt_regs
struct task_struct *p;
unsigned long clone_flags;
unsigned long newsp;
- int *user_tid;
+ int *parent_tidptr, *child_tidptr;
clone_flags = regs.ebx;
newsp = regs.ecx;
- user_tid = (int *)regs.edx;
+ parent_tidptr = (int *)regs.edx;
+ child_tidptr = (int *)regs.edi;
if (!newsp)
newsp = regs.esp;
- p = do_fork(clone_flags & ~CLONE_IDLETASK, newsp, ®s, 0, user_tid);
+ p = do_fork(clone_flags & ~CLONE_IDLETASK, newsp, ®s, 0, parent_tidptr, child_tidptr);
return IS_ERR(p) ? PTR_ERR(p) : p->pid;
}
@@ -536,7 +536,7 @@ asmlinkage int sys_vfork(struct pt_regs
{
struct task_struct *p;
- p = do_fork(CLONE_VFORK | CLONE_VM | SIGCHLD, regs.esp, ®s, 0, NULL);
+ p = do_fork(CLONE_VFORK | CLONE_VM | SIGCHLD, regs.esp, ®s, 0, NULL, NULL);
return IS_ERR(p) ? PTR_ERR(p) : p->pid;
}
diff --exclude-from=/home/ldb/src/linux-exclude -urNdp linux-2.5.48_ldb_no_tid/arch/i386/kernel/smpboot.c linux-2.5.48_ldb/arch/i386/kernel/smpboot.c
--- linux-2.5.48_ldb_no_tid/arch/i386/kernel/smpboot.c 2002-11-18 05:29:45.000000000 +0100
+++ linux-2.5.48_ldb/arch/i386/kernel/smpboot.c 2002-11-20 14:55:19.000000000 +0100
@@ -498,7 +498,7 @@ static struct task_struct * __init fork_
* don't care about the eip and regs settings since
* we'll never reschedule the forked task.
*/
- return do_fork(CLONE_VM|CLONE_IDLETASK, 0, ®s, 0, NULL);
+ return do_fork(CLONE_VM|CLONE_IDLETASK, 0, ®s, 0, NULL, NULL);
}
/* which physical APIC ID maps to which logical CPU number */
diff --exclude-from=/home/ldb/src/linux-exclude -urNdp linux-2.5.48_ldb_no_tid/include/linux/sched.h linux-2.5.48_ldb/include/linux/sched.h
--- linux-2.5.48_ldb_no_tid/include/linux/sched.h 2002-11-18 05:29:22.000000000 +0100
+++ linux-2.5.48_ldb/include/linux/sched.h 2002-11-20 15:31:55.000000000 +0100
@@ -46,10 +46,11 @@ struct exec_domain;
#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_CLEARTID 0x00200000 /* clear the userspace TID */
-#define CLONE_DETACHED 0x00400000 /* parent wants no child-exit signal */
-#define CLONE_UNTRACED 0x00800000 /* set if the tracing process can't force CLONE_PTRACE on this clone */
+#define CLONE_PARENT_SETTID 0x00100000 /* set the TID in the parent */
+#define CLONE_CHILD_CLEARTID 0x00200000 /* clear the TID in the child */
+#define CLONE_DETACHED 0x00400000 /* parent wants no child-exit signal */
+#define CLONE_UNTRACED 0x00800000 /* set if the tracing process can't force CLONE_PTRACE on this clone */
+#define CLONE_CHILD_SETTID 0x01000000 /* set the TID in the child */
/*
* List of flags we want to share for kernel threads,
@@ -332,7 +333,7 @@ struct task_struct {
wait_queue_head_t wait_chldexit; /* for wait4() */
struct completion *vfork_done; /* for vfork() */
- int *user_tid; /* for CLONE_CLEARTID */
+ int *user_tid; /* CLONE_CHILD_CLEARTID */
unsigned long rt_priority;
unsigned long it_real_value, it_prof_value, it_virt_value;
@@ -615,7 +616,7 @@ extern void daemonize(void);
extern task_t *child_reaper;
extern int do_execve(char *, char **, char **, struct pt_regs *);
-extern struct task_struct *do_fork(unsigned long, unsigned long, struct pt_regs *, unsigned long, int *);
+extern struct task_struct *do_fork(unsigned long, unsigned long, struct pt_regs *, unsigned long, int *, int *);
#ifdef CONFIG_SMP
extern void wait_task_inactive(task_t * p);
diff --exclude-from=/home/ldb/src/linux-exclude -urNdp linux-2.5.48_ldb_no_tid/kernel/fork.c linux-2.5.48_ldb/kernel/fork.c
--- linux-2.5.48_ldb_no_tid/kernel/fork.c 2002-11-18 17:08:55.000000000 +0100
+++ linux-2.5.48_ldb/kernel/fork.c 2002-11-20 15:55:10.000000000 +0100
@@ -409,15 +409,15 @@ void mm_release(void)
complete(vfork_done);
}
if (tsk->user_tid) {
- int * user_tid = tsk->user_tid;
+ int * tidptr = tsk->user_tid;
tsk->user_tid = NULL;
/*
* We dont check the error code - if userspace has
* not set up a proper pointer then tough luck.
*/
- put_user(0, user_tid);
- sys_futex((unsigned long)user_tid, FUTEX_WAKE, 1, NULL);
+ __put_user(0, tidptr);
+ sys_futex((unsigned long)tidptr, FUTEX_WAKE, 1, NULL);
}
}
@@ -680,9 +680,9 @@ static inline void copy_flags(unsigned l
p->flags = new_flags;
}
-asmlinkage int sys_set_tid_address(int *user_tid)
+asmlinkage int sys_set_tid_address(int *tidptr)
{
- current->user_tid = user_tid;
+ current->user_tid = tidptr;
return current->pid;
}
@@ -699,7 +699,8 @@ static struct task_struct *copy_process(
unsigned long stack_start,
struct pt_regs *regs,
unsigned long stack_size,
- int *user_tid)
+ int *parent_tidptr,
+ int *child_tidptr)
{
int retval;
struct task_struct *p = NULL;
@@ -716,6 +717,10 @@ static struct task_struct *copy_process(
if ((clone_flags & CLONE_DETACHED) && !(clone_flags & CLONE_THREAD))
return ERR_PTR(-EINVAL);
+ if ((clone_flags & (CLONE_CHILD_SETTID | CLONE_CHILD_CLEARTID))
+ && (retval = verify_area(VERIFY_WRITE, child_tidptr, sizeof(int))))
+ return ERR_PTR(retval);
+
retval = security_ops->task_create(clone_flags);
if (retval)
goto fork_out;
@@ -823,19 +828,15 @@ static struct task_struct *copy_process(
retval = copy_thread(0, clone_flags, stack_start, stack_size, p, regs);
if (retval)
goto bad_fork_cleanup_namespace;
- /*
- * Notify the child of the TID?
- */
+
retval = -EFAULT;
- if (clone_flags & CLONE_SETTID)
- if (put_user(p->pid, user_tid))
+ if (clone_flags & CLONE_PARENT_SETTID)
+ if (put_user(p->pid, parent_tidptr))
goto bad_fork_cleanup_namespace;
-
/*
- * Does the userspace VM want the TID cleared on mm_release()?
+ * Clear TID on mm_release()?
*/
- if (clone_flags & CLONE_CLEARTID)
- p->user_tid = user_tid;
+ p->user_tid = (clone_flags & CLONE_CHILD_CLEARTID) ? child_tidptr : 0;
/*
* Syscall tracing should be turned off in the child regardless
@@ -1004,7 +1005,8 @@ struct task_struct *do_fork(unsigned lon
unsigned long stack_start,
struct pt_regs *regs,
unsigned long stack_size,
- int *user_tid)
+ int *parent_tidptr,
+ int *child_tidptr)
{
struct task_struct *p;
int trace = 0;
@@ -1015,7 +1017,7 @@ struct task_struct *do_fork(unsigned lon
clone_flags |= CLONE_PTRACE;
}
- p = copy_process(clone_flags, stack_start, regs, stack_size, user_tid);
+ p = copy_process(clone_flags, stack_start, regs, stack_size, parent_tidptr, child_tidptr);
if (!IS_ERR(p)) {
struct completion vfork;
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-
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