Re: Re: [RFC][PATCH 2/4 v4] ftrace/x86: Add save_regs for i386function calls

[Steven Rostedt]

On Thu, 2012-07-19 at 11:20 +0900, Masami Hiramatsu wrote:
> (2012/07/19 0:59), Steven Rostedt wrote:
> > On Fri, 2012-07-13 at 14:47 -0400, Steven Rostedt wrote:
> > 
> > Masami, can you give your Reviewed-by tag for this version? Or is there
> > something else needing to be fixed?
> 
> No, that is OK for me. I've just missed that...
> 
> Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
> 
> Thank you!
> 

Thanks! Except I have one more version. Someone offlist gave me some
ideas.

Here's the diff from the previous patch.

diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index 46caa56..ca5a146 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -1169,10 +1169,9 @@ ENTRY(ftrace_regs_caller)
 	movl $__KERNEL_CS,13*4(%esp)
 
 	movl 12*4(%esp), %eax	/* Load ip (1st parameter) */
-	movl 0x4(%ebp), %edx	/* Load parent ip (2cd parameter) */
-	lea  (%esp), %ecx
-	pushl %ecx		/* Save pt_regs as 4th parameter */
+	movl 0x4(%ebp), %edx	/* Load parent ip (2nd parameter) */
 	leal function_trace_op, %ecx /* Save ftrace_pos in 3rd parameter */
+	pushl %esp		/* Save pt_regs as 4th parameter */
 
 GLOBAL(ftrace_regs_call)
 	call ftrace_stub
@@ -1195,8 +1194,8 @@ GLOBAL(ftrace_regs_call)
 	popl %es
 	popl %fs
 	popl %gs
-	addl $8, %esp		/* Skip orig_ax and ip */
-	popf			/* Pop flags at end (no addl to corrupt flags) */
+	lea 8(%esp), %esp	/* Skip orig_ax and ip */
+	popf			/* Pop flags at end */
 	jmp ftrace_ret
 
 ftrace_restore_flags:


Because we no longer have that 4 byte offset on the stack when we need
to load the 4th parameter, we can just load the current stack pointer
into the stack (pushl %esp), without the save to %ecx step.

also, because lea is faster than add (and doesn't even modify flags), I
changed the last part to use lea instead of addl.

Can you give your reviewed-by tag for this too? I'd like to push this
out today so we can still make 3.6.

Thanks!

-- Steve

here's the full patch:

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..ca5a146 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 +1135,72 @@ ftrace_stub:
 	ret
 END(ftrace_caller)
 
+ENTRY(ftrace_regs_caller)
+	pushf	/* push flags before compare (in cs location) */
+	cmpl $0, function_trace_stop
+	jne ftrace_restore_flags
+
+	/*
+	 * i386 does not save SS and ESP when coming from kernel.
+	 * Instead, to get sp, &regs->sp is used (see ptrace.h).
+	 * Unfortunately, that means eflags must be at the same location
+	 * as the current return ip is. We move the return ip into the
+	 * ip location, and move flags into the return ip location.
+	 */
+	pushl 4(%esp)	/* save return ip into ip slot */
+	subl $MCOUNT_INSN_SIZE, (%esp)	/* Adjust ip */
+
+	pushl $0	/* Load 0 into orig_ax */
+	pushl %gs
+	pushl %fs
+	pushl %es
+	pushl %ds
+	pushl %eax
+	pushl %ebp
+	pushl %edi
+	pushl %esi
+	pushl %edx
+	pushl %ecx
+	pushl %ebx
+
+	movl 13*4(%esp), %eax	/* Get the saved flags */
+	movl %eax, 14*4(%esp)	/* Move saved flags into regs->flags location */
+				/* clobbering return ip */
+	movl $__KERNEL_CS,13*4(%esp)
+
+	movl 12*4(%esp), %eax	/* Load ip (1st parameter) */
+	movl 0x4(%ebp), %edx	/* Load parent ip (2nd parameter) */
+	leal function_trace_op, %ecx /* Save ftrace_pos in 3rd parameter */
+	pushl %esp		/* Save pt_regs as 4th parameter */
+
+GLOBAL(ftrace_regs_call)
+	call ftrace_stub
+
+	addl $4, %esp		/* Skip pt_regs */
+	movl 14*4(%esp), %eax	/* Move flags back into cs */
+	movl %eax, 13*4(%esp)	/* Needed to keep addl from modifying flags */
+	movl 12*4(%esp), %eax	/* Get return ip from regs->ip */
+	addl $MCOUNT_INSN_SIZE, %eax
+	movl %eax, 14*4(%esp)	/* Put return ip back for ret */
+
+	popl %ebx
+	popl %ecx
+	popl %edx
+	popl %esi
+	popl %edi
+	popl %ebp
+	popl %eax
+	popl %ds
+	popl %es
+	popl %fs
+	popl %gs
+	lea 8(%esp), %esp	/* Skip orig_ax and ip */
+	popf			/* Pop flags at end */
+	jmp ftrace_ret
+
+ftrace_restore_flags:
+	popf
+	jmp  ftrace_stub
 #else /* ! CONFIG_DYNAMIC_FTRACE */
 
 ENTRY(mcount)
diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index b90eb1a..1d41402 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -206,7 +206,6 @@ static int
 ftrace_modify_code(unsigned long ip, unsigned const char *old_code,
 		   unsigned const char *new_code);
 
-#ifdef ARCH_SUPPORTS_FTRACE_SAVE_REGS
 /*
  * Should never be called:
  *  As it is only called by __ftrace_replace_code() which is called by
@@ -221,7 +220,6 @@ int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
 	WARN_ON(1);
 	return -EINVAL;
 }
-#endif
 
 int ftrace_update_ftrace_func(ftrace_func_t func)
 {
@@ -237,7 +235,6 @@ int ftrace_update_ftrace_func(ftrace_func_t func)
 
 	ret = ftrace_modify_code(ip, old, new);
 
-#ifdef ARCH_SUPPORTS_FTRACE_SAVE_REGS
 	/* Also update the regs callback function */
 	if (!ret) {
 		ip = (unsigned long)(&ftrace_regs_call);
@@ -245,7 +242,6 @@ int ftrace_update_ftrace_func(ftrace_func_t func)
 		new = ftrace_call_replace(ip, (unsigned long)func);
 		ret = ftrace_modify_code(ip, old, new);
 	}
-#endif
 
 	atomic_dec(&modifying_ftrace_code);
 



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