(2012/07/12 4:50), Steven Rostedt wrote:
> From: Steven Rostedt <[email protected]>
>
> Add saving full regs for function tracing on i386.
> The saving of regs was influenced by patches sent out by
> Masami Hiramatsu.
>
> Cc: Masami Hiramatsu <[email protected]>
> Signed-off-by: Steven Rostedt <[email protected]>
> ---
> arch/x86/include/asm/ftrace.h | 2 --
> arch/x86/kernel/entry_32.S | 58
> +++++++++++++++++++++++++++++++++++++++++
> arch/x86/kernel/ftrace.c | 4 ---
> 3 files changed, 58 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/include/asm/ftrace.h b/arch/x86/include/asm/ftrace.h
> index a847501..a6cae0c 100644
> --- a/arch/x86/include/asm/ftrace.h
> +++ b/arch/x86/include/asm/ftrace.h
> @@ -40,10 +40,8 @@
>
> #ifdef CONFIG_DYNAMIC_FTRACE
> #define ARCH_SUPPORTS_FTRACE_OPS 1
> -#ifdef CONFIG_X86_64
> #define ARCH_SUPPORTS_FTRACE_SAVE_REGS
> #endif
> -#endif
>
> #ifndef __ASSEMBLY__
> extern void mcount(void);
> diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
> index 5da11d1..8ef138f 100644
> --- a/arch/x86/kernel/entry_32.S
> +++ b/arch/x86/kernel/entry_32.S
> @@ -1123,6 +1123,7 @@ ftrace_call:
> popl %edx
> popl %ecx
> popl %eax
> +ftrace_ret:
> #ifdef CONFIG_FUNCTION_GRAPH_TRACER
> .globl ftrace_graph_call
> ftrace_graph_call:
> @@ -1134,6 +1135,63 @@ ftrace_stub:
> ret
> END(ftrace_caller)
>
> +ENTRY(ftrace_regs_caller)
> + pushf /* push flags before compare (in ss location) */
> + cmpl $0, function_trace_stop
> + jne ftrace_restore_flags
> +
> + pushl %esp /* Save stack in sp location */
> + subl $4, (%esp) /* Adjust saved stack to skip saved flags */
> + pushl 4(%esp) /* Save flags in correct position */
> + movl $__KERNEL_DS, 8(%esp) /* Save ss */
> + pushl $__KERNEL_CS
> + pushl 4*4(%esp) /* Save the ip */
> + subl $MCOUNT_INSN_SIZE, (%esp) /* Adjust ip */
> + pushl $0 /* Load 0 into orig_ax */
Oops, you might forget that the i386's interrupt stack layout is a bit
different from x86-64.
On x86-64, regs->sp directly points the top of stack.
On the other hand (i386), regs->sp IS the top of stack. You can see
below code in arch/x86/include/asm/ptrace.h
---
/*
* X86_32 CPUs don't save ss and esp if the CPU is already in kernel mode
* when it traps. The previous stack will be directly underneath the saved
* registers, and 'sp/ss' won't even have been saved. Thus the '®s->sp'.
*
* This is valid only for kernel mode traps.
*/
static inline unsigned long kernel_stack_pointer(struct pt_regs *regs)
{
#ifdef CONFIG_X86_32
return (unsigned long)(®s->sp);
#else
return regs->sp;
#endif
}
---
This means that you need a trick here.
sp-> [retaddr]
(*)-> [orig_stack]
Here is the stack layout when the ftrace_regs_caller is called.
(*) points the original stack pointer. this means that regs->sp has
placed at (*). After doing pushf, it changed as below.
(what user expects)
sp-> [flags] <- regs.cs
[retaddr] <- regs.flags
(*)-> [orig_stack] <- regs.sp
So we have to change this stack layout as the user expected. That is
what I did it in my previous series;
https://lkml.org/lkml/2012/6/5/119
In this patch, I clobbered the return address on the stack and
stores it in the local stack because of that reason.
+ movl 14*4(%esp), %eax /* Load return address */
+ pushl %eax /* Save return address (+4) */
+ subl $MCOUNT_INSN_SIZE, %eax
+ movl %eax, 12*4+4(%esp) /* Store IP */
+ movl 13*4+4(%esp), %edx /* Load flags */
+ movl %edx, 14*4+4(%esp) /* Store flags */
+ movl $__KERNEL_CS, %edx
+ movl %edx, 13*4+4(%esp)
Thank you,
--
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: [email protected]
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
