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Message-ID: <20170512210529.GA29693@nuc>
Date: Fri, 12 May 2017 22:05:29 +0100
From: Abel Vesa <abelvesa@...il.com>
To: robin.murphy@....com, jjhiblot@...phandler.com,
nicstange@...il.com, Russell King <linux@...linux.org.uk>,
Steven Rostedt <rostedt@...dmis.org>,
Ingo Molnar <mingo@...hat.com>
Cc: pmladek@...e.com, mhiramat@...nel.org,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm: ftrace: Adds support for
CONFIG_DYNAMIC_FTRACE_WITH_REGS
On Fri, May 12, 2017 at 09:38:37PM +0100, abelvesa@...il.com wrote:
> From: Abel Vesa <abelvesa@...il.com>
To be ignored, wrong git config. Will send another one without the From line.
>
> 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: Abel Vesa <abelvesa@...il.com>
> ---
> arch/arm/Kconfig | 1 +
> arch/arm/include/asm/ftrace.h | 4 ++
> arch/arm/kernel/entry-ftrace.S | 100 +++++++++++++++++++++++++++++++++++++++++
> arch/arm/kernel/ftrace.c | 37 +++++++++++++++
> 4 files changed, 142 insertions(+)
>
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 4c1a35f..730d456 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -56,6 +56,7 @@ config ARM
> select HAVE_DMA_API_DEBUG
> select HAVE_DMA_CONTIGUOUS if MMU
> select HAVE_DYNAMIC_FTRACE if (!XIP_KERNEL) && !CPU_ENDIAN_BE32 && MMU
> + 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_EXIT_THREAD
> select HAVE_FTRACE_MCOUNT_RECORD if (!XIP_KERNEL)
> diff --git a/arch/arm/include/asm/ftrace.h b/arch/arm/include/asm/ftrace.h
> index 22b7311..f379881 100644
> --- a/arch/arm/include/asm/ftrace.h
> +++ b/arch/arm/include/asm/ftrace.h
> @@ -1,6 +1,10 @@
> #ifndef _ASM_ARM_FTRACE
> #define _ASM_ARM_FTRACE
>
> +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
> +#define ARCH_SUPPORTS_FTRACE_OPS 1
> +#endif
> +
> #ifdef CONFIG_FUNCTION_TRACER
> #define MCOUNT_ADDR ((unsigned long)(__gnu_mcount_nc))
> #define MCOUNT_INSN_SIZE 4 /* sizeof mcount call */
> diff --git a/arch/arm/kernel/entry-ftrace.S b/arch/arm/kernel/entry-ftrace.S
> index c73c403..efcd9f2 100644
> --- a/arch/arm/kernel/entry-ftrace.S
> +++ b/arch/arm/kernel/entry-ftrace.S
> @@ -92,12 +92,95 @@
> 2: mcount_exit
> .endm
>
> +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
> +
> +.macro __ftrace_regs_caller
> +
> + sub sp, sp, #8 @ space for PC and CPSR OLD_R0,
> + @ OLD_R0 will overwrite previous LR
> +
> + add ip, sp, #12 @ move in IP the value of SP as it was
> + @ before the push {lr} of the mcount mechanism
> +
> + str lr, [sp, #0] @ store LR instead of PC
> +
> + ldr lr, [sp, #8] @ get previous LR
> +
> + str r0, [sp, #8] @ write r0 as OLD_R0 over previous LR
> +
> + stmdb sp!, {ip, lr}
> + stmdb sp!, {r0-r11, lr}
> +
> + @ stack content at this point:
> + @ 0 4 48 52 56 60 64 68 72
> + @ R0 | R1 | ... | LR | SP + 4 | previous LR | LR | PSR | OLD_R0 |
> +
> + mov r3, sp @ struct pt_regs*
> +
> + ldr r2, =function_trace_op
> + ldr r2, [r2] @ pointer to the current
> + @ function tracing op
> +
> + ldr r1, [sp, #S_LR] @ lr of instrumented func
> +
> + ldr lr, [sp, #S_PC] @ get LR
> +
> + 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
> +
> + @ pop saved regs
> + ldmia sp!, {r0-r12} @ restore r0 through r12
> + ldr ip, [sp, #8] @ restore PC
> + ldr lr, [sp, #4] @ restore LR
> + ldr sp, [sp, #0] @ restore SP
> + mov pc, ip @ return
> +.endm
> +
> +#ifdef CONFIG_FUNCTION_GRAPH_TRACER
> +.macro __ftrace_graph_regs_caller
> +
> + sub r0, fp, #4 @ lr of instrumented routine (parent)
> +
> + @ called from __ftrace_regs_caller
> + ldr r1, [sp, #S_PC] @ instrumented routine (func)
> + mcount_adjust_addr r1, r1
> +
> + mov r2, fp @ frame pointer
> + bl prepare_ftrace_return
> +
> + @ pop registers saved in ftrace_regs_caller
> + ldmia sp!, {r0-r12} @ restore r0 through r12
> + ldr ip, [sp, #8] @ restore PC
> + ldr lr, [sp, #4] @ restore LR
> + ldr sp, [sp, #0] @ restore SP
> + mov pc, ip @ return
> +
> +.endm
> +#endif
> +#endif
> +
> .macro __ftrace_caller suffix
> mcount_enter
>
> mcount_get_lr r1 @ lr of instrumented func
> mcount_adjust_addr r0, lr @ instrumented function
>
> +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
> + ldr r2, =function_trace_op
> + ldr r2, [r2] @ pointer to the current
> + @ function tracing op
> + mov r3, #0 @ regs is NULL
> +#endif
> +
> .globl ftrace_call\suffix
> ftrace_call\suffix:
> bl ftrace_stub
> @@ -212,6 +295,15 @@ UNWIND(.fnstart)
> __ftrace_caller
> UNWIND(.fnend)
> ENDPROC(ftrace_caller)
> +
> +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
> +ENTRY(ftrace_regs_caller)
> +UNWIND(.fnstart)
> + __ftrace_regs_caller
> +UNWIND(.fnend)
> +ENDPROC(ftrace_regs_caller)
> +#endif
> +
> #endif
>
> #ifdef CONFIG_FUNCTION_GRAPH_TRACER
> @@ -220,6 +312,14 @@ UNWIND(.fnstart)
> __ftrace_graph_caller
> UNWIND(.fnend)
> ENDPROC(ftrace_graph_caller)
> +
> +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
> +ENTRY(ftrace_graph_regs_caller)
> +UNWIND(.fnstart)
> + __ftrace_graph_regs_caller
> +UNWIND(.fnend)
> +ENDPROC(ftrace_graph_regs_caller)
> +#endif
> #endif
>
> .purgem mcount_enter
> diff --git a/arch/arm/kernel/ftrace.c b/arch/arm/kernel/ftrace.c
> index 833c991..5617932 100644
> --- a/arch/arm/kernel/ftrace.c
> +++ b/arch/arm/kernel/ftrace.c
> @@ -141,6 +141,15 @@ int ftrace_update_ftrace_func(ftrace_func_t func)
>
> ret = ftrace_modify_code(pc, 0, new, false);
>
> +#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
> +
> #ifdef CONFIG_OLD_MCOUNT
> if (!ret) {
> pc = (unsigned long)&ftrace_call_old;
> @@ -159,11 +168,29 @@ 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);
> +}
> +
> +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
> +
> +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);
> }
>
> +#endif
> +
> int ftrace_make_nop(struct module *mod,
> struct dyn_ftrace *rec, unsigned long addr)
> {
> @@ -231,6 +258,8 @@ 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)
> @@ -253,6 +282,14 @@ static int ftrace_modify_graph_caller(bool enable)
> ftrace_graph_caller,
> enable);
>
> +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
> + if (!ret)
> + ret = __ftrace_modify_caller(&ftrace_graph_regs_call,
> + ftrace_graph_regs_caller,
> + enable);
> +#endif
> +
> +
> #ifdef CONFIG_OLD_MCOUNT
> if (!ret)
> ret = __ftrace_modify_caller(&ftrace_graph_call_old,
> --
> 2.7.4
>
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