[PATCH] tile: support GENERIC_KERNEL_THREAD and GENERIC_KERNEL_EXECVE

From: Chris Metcalf
Date: Fri Oct 19 2012 - 16:40:58 EST

Also provide an optimized current_pt_regs() while we're at it.

Signed-off-by: Chris Metcalf <cmetcalf@xxxxxxxxxx>
---
[Re-sending to correct linus-arch / linux-arch typo.]

arch/tile/Kconfig | 2 +
arch/tile/include/asm/processor.h | 3 ++
arch/tile/include/asm/switch_to.h | 5 +-
arch/tile/kernel/entry.S | 11 ----
arch/tile/kernel/intvec_32.S | 15 ++++++
arch/tile/kernel/intvec_64.S | 15 ++++++
arch/tile/kernel/process.c | 103 ++++++++++++++-----------------------
7 files changed, 78 insertions(+), 76 deletions(-)

diff --git a/arch/tile/Kconfig b/arch/tile/Kconfig
index 875d008..ea7f61e 100644
--- a/arch/tile/Kconfig
+++ b/arch/tile/Kconfig
@@ -21,6 +21,8 @@ config TILE
select ARCH_HAVE_NMI_SAFE_CMPXCHG
select GENERIC_CLOCKEVENTS
select MODULES_USE_ELF_RELA
+ select GENERIC_KERNEL_THREAD
+ select GENERIC_KERNEL_EXECVE

# FIXME: investigate whether we need/want these options.
# select HAVE_IOREMAP_PROT
diff --git a/arch/tile/include/asm/processor.h b/arch/tile/include/asm/processor.h
index 8c4dd9f..9a83e53 100644
--- a/arch/tile/include/asm/processor.h
+++ b/arch/tile/include/asm/processor.h
@@ -239,6 +239,9 @@ unsigned long get_wchan(struct task_struct *p);
#define KSTK_TOP(task) (task_ksp0(task) - STACK_TOP_DELTA)
#define task_pt_regs(task) \
((struct pt_regs *)(task_ksp0(task) - KSTK_PTREGS_GAP) - 1)
+#define current_pt_regs() \
+ ((struct pt_regs *)((stack_pointer | (THREAD_SIZE - 1)) - \
+ (KSTK_PTREGS_GAP - 1)) - 1)
#define task_sp(task) (task_pt_regs(task)->sp)
#define task_pc(task) (task_pt_regs(task)->pc)
/* Aliases for pc and sp (used in fs/proc/array.c) */
diff --git a/arch/tile/include/asm/switch_to.h b/arch/tile/include/asm/switch_to.h
index 1d48c5f..b8f888c 100644
--- a/arch/tile/include/asm/switch_to.h
+++ b/arch/tile/include/asm/switch_to.h
@@ -68,7 +68,10 @@ extern unsigned long get_switch_to_pc(void);
/* Support function for forking a new task. */
void ret_from_fork(void);

-/* Called from ret_from_fork() when a new process starts up. */
+/* Support function for forking a new kernel thread. */
+void ret_from_kernel_thread(void *fn, void *arg);
+
+/* Called from ret_from_xxx() when a new process starts up. */
struct task_struct *sim_notify_fork(struct task_struct *prev);

#endif /* !__ASSEMBLY__ */
diff --git a/arch/tile/kernel/entry.S b/arch/tile/kernel/entry.S
index c31637b..f116cb0 100644
--- a/arch/tile/kernel/entry.S
+++ b/arch/tile/kernel/entry.S
@@ -28,17 +28,6 @@ STD_ENTRY(current_text_addr)
STD_ENDPROC(current_text_addr)

/*
- * Implement execve(). The i386 code has a note that forking from kernel
- * space results in no copy on write until the execve, so we should be
- * careful not to write to the stack here.
- */
-STD_ENTRY(kernel_execve)
- moveli TREG_SYSCALL_NR_NAME, __NR_execve
- swint1
- jrp lr
- STD_ENDPROC(kernel_execve)
-
-/*
* We don't run this function directly, but instead copy it to a page
* we map into every user process. See vdso_setup().
*
diff --git a/arch/tile/kernel/intvec_32.S b/arch/tile/kernel/intvec_32.S
index 6943515..58aad51 100644
--- a/arch/tile/kernel/intvec_32.S
+++ b/arch/tile/kernel/intvec_32.S
@@ -1291,6 +1291,21 @@ STD_ENTRY(ret_from_fork)
}
STD_ENDPROC(ret_from_fork)

+STD_ENTRY(ret_from_kernel_thread)
+ jal sim_notify_fork
+ jal schedule_tail
+ FEEDBACK_REENTER(ret_from_fork)
+ {
+ move r0, r31
+ jalr r30
+ }
+ FEEDBACK_REENTER(ret_from_kernel_thread)
+ {
+ movei r30, 0 /* not an NMI */
+ j .Lresume_userspace /* jump into middle of interrupt_return */
+ }
+ STD_ENDPROC(ret_from_kernel_thread)
+
/*
* Code for ill interrupt.
*/
diff --git a/arch/tile/kernel/intvec_64.S b/arch/tile/kernel/intvec_64.S
index 7c06d59..a84911c 100644
--- a/arch/tile/kernel/intvec_64.S
+++ b/arch/tile/kernel/intvec_64.S
@@ -1150,6 +1150,21 @@ STD_ENTRY(ret_from_fork)
}
STD_ENDPROC(ret_from_fork)

+STD_ENTRY(ret_from_kernel_thread)
+ jal sim_notify_fork
+ jal schedule_tail
+ FEEDBACK_REENTER(ret_from_fork)
+ {
+ move r0, r31
+ jalr r30
+ }
+ FEEDBACK_REENTER(ret_from_kernel_thread)
+ {
+ movei r30, 0 /* not an NMI */
+ j .Lresume_userspace /* jump into middle of interrupt_return */
+ }
+ STD_ENDPROC(ret_from_kernel_thread)
+
/* Various stub interrupt handlers and syscall handlers */

STD_ENTRY_LOCAL(_kernel_double_fault)
diff --git a/arch/tile/kernel/process.c b/arch/tile/kernel/process.c
index 307d010..ca6de8d 100644
--- a/arch/tile/kernel/process.c
+++ b/arch/tile/kernel/process.c
@@ -157,24 +157,44 @@ void arch_release_thread_info(struct thread_info *info)
static void save_arch_state(struct thread_struct *t);

int copy_thread(unsigned long clone_flags, unsigned long sp,
- unsigned long stack_size,
+ unsigned long arg,
struct task_struct *p, struct pt_regs *regs)
{
- struct pt_regs *childregs;
+ struct pt_regs *childregs = task_pt_regs(p);
unsigned long ksp;
+ unsigned long *callee_regs;

/*
- * When creating a new kernel thread we pass sp as zero.
- * Assign it to a reasonable value now that we have the stack.
+ * Set up the stack and stack pointer appropriately for the
+ * new child to find itself woken up in __switch_to().
+ * The callee-saved registers must be on the stack to be read;
+ * the new task will then jump to assembly support to handle
+ * calling schedule_tail(), etc., and (for userspace tasks)
+ * returning to the context set up in the pt_regs.
*/
- if (sp == 0 && regs->ex1 == PL_ICS_EX1(KERNEL_PL, 0))
- sp = KSTK_TOP(p);
+ ksp = (unsigned long) childregs;
+ ksp -= C_ABI_SAVE_AREA_SIZE; /* interrupt-entry save area */
+ ((long *)ksp)[0] = ((long *)ksp)[1] = 0;
+ ksp -= CALLEE_SAVED_REGS_COUNT * sizeof(unsigned long);
+ callee_regs = (unsigned long *)ksp;
+ ksp -= C_ABI_SAVE_AREA_SIZE; /* __switch_to() save area */
+ ((long *)ksp)[0] = ((long *)ksp)[1] = 0;
+ p->thread.ksp = ksp;

- /*
- * Do not clone step state from the parent; each thread
- * must make its own lazily.
- */
- task_thread_info(p)->step_state = NULL;
+ /* Record the pid of the task that created this one. */
+ p->thread.creator_pid = current->pid;
+
+ if (unlikely(!regs)) {
+ /* kernel thread */
+ memset(childregs, 0, sizeof(struct pt_regs));
+ memset(&callee_regs[2], 0,
+ (CALLEE_SAVED_REGS_COUNT - 2) * sizeof(unsigned long));
+ callee_regs[0] = sp; /* r30 = function */
+ callee_regs[1] = arg; /* r31 = arg */
+ childregs->ex1 = PL_ICS_EX1(KERNEL_PL, 0);
+ p->thread.pc = (unsigned long) ret_from_kernel_thread;
+ return 0;
+ }

/*
* Start new thread in ret_from_fork so it schedules properly
@@ -182,20 +202,24 @@ int copy_thread(unsigned long clone_flags, unsigned long sp,
*/
p->thread.pc = (unsigned long) ret_from_fork;

+ /*
+ * Do not clone step state from the parent; each thread
+ * must make its own lazily.
+ */
+ task_thread_info(p)->step_state = NULL;
+
/* Save user stack top pointer so we can ID the stack vm area later. */
p->thread.usp0 = sp;

- /* Record the pid of the process that created this one. */
- p->thread.creator_pid = current->pid;
-
/*
* Copy the registers onto the kernel stack so the
* return-from-interrupt code will reload it into registers.
*/
- childregs = task_pt_regs(p);
*childregs = *regs;
childregs->regs[0] = 0; /* return value is zero */
childregs->sp = sp; /* override with new user stack pointer */
+ memcpy(callee_regs, &regs->regs[CALLEE_SAVED_FIRST_REG],
+ CALLEE_SAVED_REGS_COUNT * sizeof(unsigned long));

/*
* If CLONE_SETTLS is set, set "tp" in the new task to "r4",
@@ -204,24 +228,6 @@ int copy_thread(unsigned long clone_flags, unsigned long sp,
if (clone_flags & CLONE_SETTLS)
childregs->tp = regs->regs[4];

- /*
- * Copy the callee-saved registers from the passed pt_regs struct
- * into the context-switch callee-saved registers area.
- * This way when we start the interrupt-return sequence, the
- * callee-save registers will be correctly in registers, which
- * is how we assume the compiler leaves them as we start doing
- * the normal return-from-interrupt path after calling C code.
- * Zero out the C ABI save area to mark the top of the stack.
- */
- ksp = (unsigned long) childregs;
- ksp -= C_ABI_SAVE_AREA_SIZE; /* interrupt-entry save area */
- ((long *)ksp)[0] = ((long *)ksp)[1] = 0;
- ksp -= CALLEE_SAVED_REGS_COUNT * sizeof(unsigned long);
- memcpy((void *)ksp, &regs->regs[CALLEE_SAVED_FIRST_REG],
- CALLEE_SAVED_REGS_COUNT * sizeof(unsigned long));
- ksp -= C_ABI_SAVE_AREA_SIZE; /* __switch_to() save area */
- ((long *)ksp)[0] = ((long *)ksp)[1] = 0;
- p->thread.ksp = ksp;

#if CHIP_HAS_TILE_DMA()
/*
@@ -650,37 +656,6 @@ unsigned long get_wchan(struct task_struct *p)
return 0;
}

-/*
- * We pass in lr as zero (cleared in kernel_thread) and the caller
- * part of the backtrace ABI on the stack also zeroed (in copy_thread)
- * so that backtraces will stop with this function.
- * Note that we don't use r0, since copy_thread() clears it.
- */
-static void start_kernel_thread(int dummy, int (*fn)(int), int arg)
-{
- do_exit(fn(arg));
-}
-
-/*
- * Create a kernel thread
- */
-int kernel_thread(int (*fn)(void *), void * arg, unsigned long flags)
-{
- struct pt_regs regs;
-
- memset(&regs, 0, sizeof(regs));
- regs.ex1 = PL_ICS_EX1(KERNEL_PL, 0); /* run at kernel PL, no ICS */
- regs.pc = (long) start_kernel_thread;
- regs.flags = PT_FLAGS_CALLER_SAVES; /* need to restore r1 and r2 */
- regs.regs[1] = (long) fn; /* function pointer */
- regs.regs[2] = (long) arg; /* parameter register */
-
- /* Ok, create the new process.. */
- return do_fork(flags | CLONE_VM | CLONE_UNTRACED, 0, &regs,
- 0, NULL, NULL);
-}
-EXPORT_SYMBOL(kernel_thread);
-
/* Flush thread state. */
void flush_thread(void)
{
--
1.7.10.3

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