Originally the jump to kernel_thread "payload" or entry-point happened
via a return from exception (RTIE) using stuff from specially carved
pt_regs (pt_regs->status32 enabled Kernel mode, pt_regs->ret pointed to
a kernel thread helper to jump to entry point)
Now copy_thread() sets up __switch_to() to ret to a small asm trampoline
ret_from_kernel_thread() which simply jumps to thread entry point.
It also setsup thread entry point in callee regs (vs. pt_regs) which are
anyways unwound by __switch_to, keeping things ready-to-go for
ret_from_kernel_thread.
This eliminates any involvement of pt_regs altogether.
Signed-off-by: Vineet Gupta <vgupta@xxxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
---
arch/arc/Kconfig | 1 +
arch/arc/include/asm/processor.h | 6 ----
arch/arc/kernel/entry.S | 7 ++++
arch/arc/kernel/process.c | 62 +++++++++++++------------------------
4 files changed, 30 insertions(+), 46 deletions(-)
diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig
index 548b89e..5588cee 100644
--- a/arch/arc/Kconfig
+++ b/arch/arc/Kconfig
@@ -17,6 +17,7 @@ config ARC
select GENERIC_FIND_FIRST_BIT
# for now, we don't need GENERIC_IRQ_PROBE, CONFIG_GENERIC_IRQ_CHIP
select GENERIC_IRQ_SHOW
+ select GENERIC_KERNEL_THREAD
select GENERIC_PENDING_IRQ if SMP
select GENERIC_SMP_IDLE_THREAD
select HAVE_GENERIC_HARDIRQS
diff --git a/arch/arc/include/asm/processor.h b/arch/arc/include/asm/processor.h
index 053a639..860252e 100644
--- a/arch/arc/include/asm/processor.h
+++ b/arch/arc/include/asm/processor.h
@@ -57,12 +57,6 @@ unsigned long thread_saved_pc(struct task_struct *t);
#define cpu_relax() do { } while (0)
-/*
- * Create a new kernel thread
- */
-
-extern int kernel_thread(int (*fn) (void *), void *arg, unsigned long flags);
-
#define copy_segments(tsk, mm) do { } while (0)
#define release_segments(mm) do { } while (0)
diff --git a/arch/arc/kernel/entry.S b/arch/arc/kernel/entry.S
index 0324ad1..e76b432 100644
--- a/arch/arc/kernel/entry.S
+++ b/arch/arc/kernel/entry.S
@@ -579,6 +579,13 @@ ARC_ENTRY ret_from_fork
b @ret_from_exception
ARC_EXIT ret_from_fork
+ARC_ENTRY ret_from_kernel_thread
+ bl @schedule_tail
+ jl.d [r14] ; kernel_thread "payload"
+ mov r0, r13 ; arg to payload
+ j @sys_exit
+ARC_EXIT ret_from_kernel_thread
+
;################### Special Sys Call Wrappers ##########################
ARC_ENTRY sys_execve_wrapper
diff --git a/arch/arc/kernel/process.c b/arch/arc/kernel/process.c
index 5c18ba8..a468205 100644
--- a/arch/arc/kernel/process.c
+++ b/arch/arc/kernel/process.c
@@ -142,34 +142,8 @@ void cpu_idle(void)
}
}
-void kernel_thread_helper(void)
-{
- __asm__ __volatile__(
- "mov r0, r2 \n\t"
- "mov r1, r3 \n\t"
- "j [r1] \n\t");
-}
-
-int kernel_thread(int (*fn) (void *), void *arg, unsigned long flags)
-{
- struct pt_regs regs;
-
- memset(®s, 0, sizeof(regs));
-
- regs.r2 = (unsigned long)arg;
- regs.r3 = (unsigned long)fn;
- regs.blink = (unsigned long)do_exit;
- regs.ret = (unsigned long)kernel_thread_helper;
- regs.status32 = read_aux_reg(0xa);
-
- /* Ok, create the new process.. */
- return do_fork(flags | CLONE_VM | CLONE_UNTRACED, 0, ®s, 0, NULL,
- NULL);
-
-}
-EXPORT_SYMBOL(kernel_thread);
-
asmlinkage void ret_from_fork(void);
+asmlinkage void ret_from_kernel_thread(void) __attribute__((noreturn));
/* Layout of Child kernel mode stack as setup at the end of this function is
*
@@ -202,7 +176,7 @@ asmlinkage void ret_from_fork(void);
* ------------------ <===== END of PAGE
*/
int copy_thread(unsigned long clone_flags,
- unsigned long usp, unsigned long topstk,
+ unsigned long usp, unsigned long arg,
struct task_struct *p, struct pt_regs *regs)
{
struct pt_regs *c_regs; /* child's pt_regs */
@@ -216,28 +190,36 @@ int copy_thread(unsigned long clone_flags,
c_callee = ((struct callee_regs *)childksp) - 1;
/*
- * At the end of this function, kernel SP is all set for
- * switch_to to start unwinding.
- * For kernel threads we don't have callee regs, but the stack
- * layout nevertheless needs to remain the same
+ * __switch_to() uses thread.ksp to start unwinding stack
+ * For kernel threads we don't need to create callee regs, the
+ * stack layout nevertheless needs to remain the same.
+ * Also, since __switch_to anyways unwinds callee regs, we use
+ * this to populate kernel thread entry-pt/args into callee regs,
+ * so that ret_from_kernel_thread() becomes simpler.
*/
p->thread.ksp = (unsigned long)c_callee; /* THREAD_KSP */
- /* Copy parents pt regs on child's kernel mode stack */
- *c_regs = *regs;
+ if (unlikely(p->flags & PF_KTHREAD)) {
+ memset(c_regs, 0, sizeof(struct pt_regs));
- /* __switch_to expects FP(0), BLINK(return addr) at top of stack */
- childksp[0] = 0; /* for POP fp */
- childksp[1] = (unsigned long)ret_from_fork; /* for POP blink */
+ c_callee->r13 = arg; /* argument to kernel thread */
+ c_callee->r14 = usp; /* function */
- if (!(user_mode(regs))) {
- c_regs->sp =
- (unsigned long)task_thread_info(p) + (THREAD_SIZE - 4);
+ /* __switch_to expects FP(0), BLINK(return addr) at top */
+ childksp[0] = 0; /* fp */
+ childksp[1] = (unsigned long)ret_from_kernel_thread; /* blink */
return 0;
}
/*--------- User Task Only --------------*/
+ /* __switch_to expects FP(0), BLINK(return addr) at top of stack */
+ childksp[0] = 0; /* for POP fp */
+ childksp[1] = (unsigned long)ret_from_fork; /* for POP blink */
+
+ /* Copy parents pt regs on child's kernel mode stack */
+ *c_regs = *regs;
+
c_regs->sp = usp;
c_regs->r0 = 0; /* fork returns 0 in child */
--
1.7.4.1
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