Messages in this thread | | | Date | Thu, 12 Jul 2012 21:39:42 +0900 | From | Masami Hiramatsu <> | Subject | Re: [RFC][PATCH 2/4 v4] ftrace/x86: Add save_regs for i386 function calls |
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(2012/07/12 4:50), Steven Rostedt wrote: > From: Steven Rostedt <srostedt@redhat.com> > > 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 <masami.hiramatsu.pt@hitachi.com> > Signed-off-by: Steven Rostedt <rostedt@goodmis.org> > --- > 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: masami.hiramatsu.pt@hitachi.com
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