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Date:	Mon, 10 Nov 2014 09:56:17 +0100
From:	Jean-Jacques Hiblot <jjhiblot@...phandler.com>
To:	jslaby@...e.cz, linux@....linux.org.uk, rostedt@...dmis.org,
	mingo@...hat.com, nsekhar@...com, stefano.stabellini@...citrix.com,
	christoffer.dall@...aro.org
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Jean-Jacques Hiblot <jjhiblot@...phandler.com>
Subject: [PATCH v2 01/01] arm: ftrace: Adds support for CONFIG_DYNAMIC_FTRACE_WITH_REGS

The DYNAMIC_FTRACE_WITH_REGS configuration makes it possible for a ftrace
operation to specify if registers need to saved/restored by the ftrace handler.
This is needed by kgraft and possibly other ftrace-based tools, and the ARM
architecture is currently lacking this feature. It would also be the first step
to support the "Kprobes-on-ftrace" optimization on ARM.

This patch introduces a new ftrace handler that stores the registers on the
stack before calling the next stage. The registers are restored from the stack
before going back to the instrumented function.

A side-effect of this patch is to activate the support for ftrace_modify_call()
as it defines ARCH_SUPPORTS_FTRACE_OPS for the ARM architecture

Signed-off-by: Jean-Jacques Hiblot <jjhiblot@...phandler.com>
---
 arch/arm/Kconfig               |  2 ++
 arch/arm/include/asm/ftrace.h  |  3 ++
 arch/arm/kernel/entry-common.S | 68 +++++++++++++++++++++++++++++++++++++++++-
 arch/arm/kernel/ftrace.c       | 34 +++++++++++++++++++++
 4 files changed, 106 insertions(+), 1 deletion(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 32cbbd5..6f928ee 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -39,6 +39,7 @@ config ARM
 	select HAVE_DMA_ATTRS
 	select HAVE_DMA_CONTIGUOUS if MMU
 	select HAVE_DYNAMIC_FTRACE if (!XIP_KERNEL)
+	select HAVE_DYNAMIC_FTRACE_WITH_REGS if HAVE_DYNAMIC_FTRACE
 	select HAVE_EFFICIENT_UNALIGNED_ACCESS if (CPU_V6 || CPU_V6K || CPU_V7) && MMU
 	select HAVE_FTRACE_MCOUNT_RECORD if (!XIP_KERNEL)
 	select HAVE_FUNCTION_GRAPH_TRACER if (!THUMB2_KERNEL)
@@ -72,6 +73,7 @@ config ARM
 	select PERF_USE_VMALLOC
 	select RTC_LIB
 	select SYS_SUPPORTS_APM_EMULATION
+	select FRAME_POINTER if DYNAMIC_FTRACE_WITH_REGS && FUNCTION_GRAPH_TRACER
 	# Above selects are sorted alphabetically; please add new ones
 	# according to that.  Thanks.
 	help
diff --git a/arch/arm/include/asm/ftrace.h b/arch/arm/include/asm/ftrace.h
index 39eb16b..d8e9bea 100644
--- a/arch/arm/include/asm/ftrace.h
+++ b/arch/arm/include/asm/ftrace.h
@@ -10,6 +10,9 @@ extern void mcount(void);
 extern void __gnu_mcount_nc(void);
 
 #ifdef CONFIG_DYNAMIC_FTRACE
+
+#define ARCH_SUPPORTS_FTRACE_OPS 1
+
 struct dyn_arch_ftrace {
 #ifdef CONFIG_OLD_MCOUNT
 	bool	old_mcount;
diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index e52fe5a..9594fe2 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -197,7 +197,10 @@ ENDPROC(ret_from_fork)
 
 	mcount_get_lr	r1			@ lr of instrumented func
 	mcount_adjust_addr	r0, lr		@ instrumented function
-
+	ldr r2, =function_trace_op
+	ldr r2, [r2]				@ pointer to the current
+						@ function tracing op
+	mov r3, #0				@ regs is NULL
 	.globl ftrace_call\suffix
 ftrace_call\suffix:
 	bl	ftrace_stub
@@ -211,6 +214,38 @@ ftrace_graph_call\suffix:
 	mcount_exit
 .endm
 
+.macro __ftrace_regs_caller
+
+	add 	ip, sp, #4	@ move in IP the value of SP as it was
+				@ before the push {lr} of the mcount mechanism
+	stmdb	sp!, {ip,lr,pc}
+	stmdb	sp!, {r0-r11,lr}
+	@ stack content  at this point:
+	@ 0  4         44    48   52       56   60   64
+	@ RO | R1 | ... | R11 | LR | SP + 4 | LR | PC | previous LR |
+
+	mov r3, sp				@ struct pt_regs*
+	ldr r2, =function_trace_op
+	ldr r2, [r2]				@ pointer to the current
+						@ function tracing op
+	ldr	r1, [sp, #64]			@ lr of instrumented func
+	mcount_adjust_addr	r0, lr		@ instrumented function
+
+	.globl ftrace_regs_call
+ftrace_regs_call:
+	bl	ftrace_stub
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+	.globl ftrace_graph_regs_call
+ftrace_graph_regs_call:
+	mov	r0, r0
+#endif
+	ldr	lr, [sp, #64]		@ get the previous LR value from stack
+	ldmia	sp, {r0-r11, ip, sp}	@ pop the saved registers INCLUDING
+					@ the stack pointer
+	ret	ip
+.endm
+
 .macro __ftrace_graph_caller
 	sub	r0, fp, #4		@ &lr of instrumented routine (&parent)
 #ifdef CONFIG_DYNAMIC_FTRACE
@@ -226,6 +261,24 @@ ftrace_graph_call\suffix:
 	mcount_exit
 .endm
 
+
+.macro __ftrace_graph_regs_caller
+
+	sub	r0, fp, #4		@ &lr of instrumented routine (&parent)
+
+	@ called from __ftrace_regs_caller
+	ldr	r1, [sp, #56]		@ instrumented routine (func)
+	mcount_adjust_addr	r1, r1
+
+	mov	r2, fp			@ frame pointer
+	bl	prepare_ftrace_return
+
+	ldr	lr, [fp, #-4]		@ restore LR from the stack
+	ldmia	sp, {r0-r11, ip, sp}	@ pop the saved registers INCLUDING
+					@ the stack pointer
+	ret	ip
+.endm
+
 #ifdef CONFIG_OLD_MCOUNT
 /*
  * mcount
@@ -312,14 +365,27 @@ UNWIND(.fnstart)
 	__ftrace_caller
 UNWIND(.fnend)
 ENDPROC(ftrace_caller)
+
+ENTRY(ftrace_regs_caller)
+UNWIND(.fnstart)
+	__ftrace_regs_caller
+UNWIND(.fnend)
+ENDPROC(ftrace_regs_caller)
 #endif
 
+
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 ENTRY(ftrace_graph_caller)
 UNWIND(.fnstart)
 	__ftrace_graph_caller
 UNWIND(.fnend)
 ENDPROC(ftrace_graph_caller)
+
+ENTRY(ftrace_graph_regs_caller)
+UNWIND(.fnstart)
+	__ftrace_graph_regs_caller
+UNWIND(.fnend)
+ENDPROC(ftrace_graph_regs_caller)
 #endif
 
 .purgem mcount_enter
diff --git a/arch/arm/kernel/ftrace.c b/arch/arm/kernel/ftrace.c
index af9a8a9..35c5743 100644
--- a/arch/arm/kernel/ftrace.c
+++ b/arch/arm/kernel/ftrace.c
@@ -130,6 +130,16 @@ int ftrace_update_ftrace_func(ftrace_func_t func)
 	}
 #endif
 
+
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
+	if (!ret) {
+		pc = (unsigned long)&ftrace_regs_call;
+		new = ftrace_call_replace(pc, (unsigned long)func);
+
+		ret = ftrace_modify_code(pc, 0, new, false);
+	}
+#endif
+
 	return ret;
 }
 
@@ -139,6 +149,20 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 	unsigned long ip = rec->ip;
 
 	old = ftrace_nop_replace(rec);
+
+	new = ftrace_call_replace(ip, adjust_address(rec, addr));
+
+	return ftrace_modify_code(rec->ip, old, new, true);
+}
+
+int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
+				unsigned long addr)
+{
+	unsigned long new, old;
+	unsigned long ip = rec->ip;
+
+	old = ftrace_call_replace(ip, adjust_address(rec, old_addr));
+
 	new = ftrace_call_replace(ip, adjust_address(rec, addr));
 
 	return ftrace_modify_code(rec->ip, old, new, true);
@@ -211,6 +235,9 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
 extern unsigned long ftrace_graph_call;
 extern unsigned long ftrace_graph_call_old;
 extern void ftrace_graph_caller_old(void);
+extern unsigned long ftrace_graph_regs_call;
+extern void ftrace_graph_regs_caller(void);
+
 
 static int __ftrace_modify_caller(unsigned long *callsite,
 				  void (*func) (void), bool enable)
@@ -240,6 +267,13 @@ static int ftrace_modify_graph_caller(bool enable)
 					     enable);
 #endif
 
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
+	if (!ret)
+		ret = __ftrace_modify_caller(&ftrace_graph_regs_call,
+				     ftrace_graph_regs_caller,
+				     enable);
+#endif
+
 	return ret;
 }
 
-- 
2.1.3

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