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Message-ID: <20100201102843.GA31714@pengutronix.de>
Date: Mon, 1 Feb 2010 11:28:43 +0100
From: Uwe Kleine-König
<u.kleine-koenig@...gutronix.de>
To: Rabin Vincent <rabin@....in>
Cc: linux-kernel@...r.kernel.org,
Abhishek Sagar <sagar.abhishek@...il.com>,
Frederic Weisbecker <fweisbec@...il.com>,
Steven Rostedt <rostedt@...dmis.org>,
Ingo Molnar <mingo@...hat.com>,
linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 2/2] ftrace: re-enable dynamic ftrace for ARM
Hi Rabin,
On Sun, Jan 31, 2010 at 11:03:16PM +0530, Rabin Vincent wrote:
> This adds mcount recording and updates dynamic ftrace for ARM to work
> with the new ftrace dyamic tracing implementation.
>
> With dynamic tracing, mcount() is implemented as a nop. Callsites are
> patched on startup with nops, and dynamically patched to call to the
> ftrace_caller() routine as needed.
>
> One oddity of the ARM implementation is that we need to handle two kinds
> of mcounts. Newer GCC versions renamed the mcount routine (to
> __gnu_mcount_nc) and changed the semantics (lr is pushed on the stack
> before the call). We detect which one is used at run-time.
>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Abhishek Sagar <sagar.abhishek@...il.com>
> Cc: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
> Signed-off-by: Rabin Vincent <rabin@....in>
> ---
> arch/arm/Kconfig | 2 +
> arch/arm/include/asm/ftrace.h | 14 +++++
> arch/arm/kernel/entry-common.S | 25 ++++++---
> arch/arm/kernel/ftrace.c | 122 ++++++++++++++++++++++++++--------------
> scripts/recordmcount.pl | 2 +
> 5 files changed, 115 insertions(+), 50 deletions(-)
>
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 4c33ca8..dc92691 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -17,6 +17,8 @@ config ARM
> select HAVE_KPROBES if (!XIP_KERNEL)
> select HAVE_KRETPROBES if (HAVE_KPROBES)
> select HAVE_FUNCTION_TRACER if (!XIP_KERNEL)
> + select HAVE_FTRACE_MCOUNT_RECORD if (!XIP_KERNEL)
> + select HAVE_DYNAMIC_FTRACE if (!XIP_KERNEL && !THUMB2_KERNEL)
> select HAVE_GENERIC_DMA_COHERENT
> select HAVE_KERNEL_GZIP
> select HAVE_KERNEL_LZO
> diff --git a/arch/arm/include/asm/ftrace.h b/arch/arm/include/asm/ftrace.h
> index 103f7ee..12f445d 100644
> --- a/arch/arm/include/asm/ftrace.h
> +++ b/arch/arm/include/asm/ftrace.h
> @@ -8,6 +8,20 @@
> #ifndef __ASSEMBLY__
> extern void mcount(void);
> extern void __gnu_mcount_nc(void);
> +
> +#ifdef CONFIG_DYNAMIC_FTRACE
> +struct dyn_arch_ftrace {
> + bool gnu_mcount;
> +};
> +
> +static inline unsigned long ftrace_call_adjust(unsigned long addr)
> +{
> + return addr;
> +}
> +
> +extern void ftrace_caller_gnu(void);
> +#endif
> +
> #endif
>
> #endif
> diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
> index 2c1db77..2a7ab14 100644
> --- a/arch/arm/kernel/entry-common.S
> +++ b/arch/arm/kernel/entry-common.S
> @@ -93,16 +93,25 @@ ENDPROC(ret_from_fork)
>
> #ifdef CONFIG_FUNCTION_TRACER
> #ifdef CONFIG_DYNAMIC_FTRACE
> +ENTRY(__gnu_mcount_nc)
> + mov ip, lr
> + ldm sp!, {lr}
> + mov pc, ip
> +
> ENTRY(mcount)
> - stmdb sp!, {r0-r3, lr}
> - mov r0, lr
> - sub r0, r0, #MCOUNT_INSN_SIZE
> + stmdb sp!, {lr}
> + ldr lr, [fp, #-4]
> + ldmia sp!, {pc}
>
> - .globl mcount_call
> -mcount_call:
> - bl ftrace_stub
> - ldr lr, [fp, #-4] @ restore lr
> - ldmia sp!, {r0-r3, pc}
> +ENTRY(ftrace_caller_gnu)
> + add sp, sp, #4
> +
> + /*
> + * We take advantage of the fact that we build with frame pointers and
> + * -mapcs-frame to combine the ftrace_caller implementations for the
> + * two mcounts with just the above adjustment. This will need to be
> + * revisited if Thumb-2 support is added.
> + */
>
> ENTRY(ftrace_caller)
> stmdb sp!, {r0-r3, lr}
> diff --git a/arch/arm/kernel/ftrace.c b/arch/arm/kernel/ftrace.c
> index c638427..1d5d268 100644
> --- a/arch/arm/kernel/ftrace.c
> +++ b/arch/arm/kernel/ftrace.c
> @@ -7,11 +7,12 @@
> *
> * Defines low-level handling of mcount calls when the kernel
> * is compiled with the -pg flag. When using dynamic ftrace, the
> - * mcount call-sites get patched lazily with NOP till they are
> - * enabled. All code mutation routines here take effect atomically.
> + * mcount call-sites get patched with NOP till they are enabled.
> + * All code mutation routines here take effect atomically.
> */
>
> #include <linux/ftrace.h>
> +#include <linux/uaccess.h>
>
> #include <asm/cacheflush.h>
> #include <asm/ftrace.h>
> @@ -20,17 +21,26 @@
> #define BL_OPCODE 0xeb000000
> #define BL_OFFSET_MASK 0x00ffffff
>
> -static unsigned long bl_insn;
> -static const unsigned long NOP = 0xe1a00000; /* mov r0, r0 */
> +#define NOP 0xe1a00000 /* mov r0, r0 */
> +#define GNU_NOP 0xe8bd4000 /* pop {lr} */
>
> -unsigned char *ftrace_nop_replace(void)
> +#define GNU_MCOUNT_ADDR ((unsigned long) __gnu_mcount_nc)
> +#define GNU_FTRACE_ADDR ((unsigned long) ftrace_caller_gnu)
> +
> +static unsigned long ftrace_nop_replace(struct dyn_ftrace *rec)
> +{
> + return rec->arch.gnu_mcount ? GNU_NOP : NOP;
> +}
> +
> +static unsigned long ftrace_caller_addr(struct dyn_ftrace *rec)
> {
> - return (char *)&NOP;
> + return rec->arch.gnu_mcount ? GNU_FTRACE_ADDR : FTRACE_ADDR;
> }
>
> /* construct a branch (BL) instruction to addr */
> -unsigned char *ftrace_call_replace(unsigned long pc, unsigned long addr)
> +static unsigned long ftrace_call_replace(unsigned long pc, unsigned long addr)
> {
> + unsigned long bl_insn;
> long offset;
>
> offset = (long)addr - (long)(pc + PC_OFFSET);
> @@ -39,65 +49,93 @@ unsigned char *ftrace_call_replace(unsigned long pc, unsigned long addr)
> * doesn't generate branches outside of kernel text.
> */
> WARN_ON_ONCE(1);
> - return NULL;
> + return 0;
> }
> offset = (offset >> 2) & BL_OFFSET_MASK;
> bl_insn = BL_OPCODE | offset;
> - return (unsigned char *)&bl_insn;
> + return bl_insn;
> }
>
> -int ftrace_modify_code(unsigned long pc, unsigned char *old_code,
> - unsigned char *new_code)
> +static int ftrace_modify_code(unsigned long pc, unsigned long old,
> + unsigned long new)
> {
> - unsigned long err = 0, replaced = 0, old, new;
> + unsigned long replaced;
>
> - old = *(unsigned long *)old_code;
> - new = *(unsigned long *)new_code;
> + if (probe_kernel_read(&replaced, (void *)pc, MCOUNT_INSN_SIZE))
> + return -EFAULT;
>
> - __asm__ __volatile__ (
> - "1: ldr %1, [%2] \n"
> - " cmp %1, %4 \n"
> - "2: streq %3, [%2] \n"
> - " cmpne %1, %3 \n"
> - " movne %0, #2 \n"
> - "3:\n"
> + if (replaced != old)
> + return -EINVAL;
>
> - ".section .fixup, \"ax\"\n"
> - "4: mov %0, #1 \n"
> - " b 3b \n"
> - ".previous\n"
> + if (probe_kernel_write((void *)pc, &new, MCOUNT_INSN_SIZE))
> + return -EPERM;
>
> - ".section __ex_table, \"a\"\n"
> - " .long 1b, 4b \n"
> - " .long 2b, 4b \n"
> - ".previous\n"
> + flush_icache_range(pc, pc + MCOUNT_INSN_SIZE);
>
> - : "=r"(err), "=r"(replaced)
> - : "r"(pc), "r"(new), "r"(old), "0"(err), "1"(replaced)
> - : "memory");
> -
> - if (!err && (replaced == old))
> - flush_icache_range(pc, pc + MCOUNT_INSN_SIZE);
> -
> - return err;
> + return 0;
> }
>
> int ftrace_update_ftrace_func(ftrace_func_t func)
> {
> - int ret;
> unsigned long pc, old;
> - unsigned char *new;
> + unsigned long new;
>
> pc = (unsigned long)&ftrace_call;
> memcpy(&old, &ftrace_call, MCOUNT_INSN_SIZE);
> new = ftrace_call_replace(pc, (unsigned long)func);
> - ret = ftrace_modify_code(pc, (unsigned char *)&old, new);
> +
> + return ftrace_modify_code(pc, old, new);
> +}
> +
> +int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
> +{
> + unsigned long new, old;
> + unsigned long ip = rec->ip;
> +
> + old = ftrace_nop_replace(rec);
> + new = ftrace_call_replace(ip, ftrace_caller_addr(rec));
> +
> + return ftrace_modify_code(rec->ip, old, new);
> +}
> +
> +static int ftrace_detect_make_nop(struct module *mod,
> + struct dyn_ftrace *rec, unsigned long addr)
> +{
> + unsigned long ip = rec->ip;
> + unsigned long call;
> + int ret;
> +
> + call = ftrace_call_replace(ip, GNU_MCOUNT_ADDR);
> + ret = ftrace_modify_code(ip, call, GNU_NOP);
> + if (!ret)
> + rec->arch.gnu_mcount = true;
> + else if (ret == -EINVAL) {
> + call = ftrace_call_replace(ip, addr);
> + ret = ftrace_modify_code(ip, call, NOP);
> + }
> +
> return ret;
> }
Wouldn't it be nice to patch out the instruction pushing lr to the
stack (in the gnu case)? Should work, shouldn't it.
Thanks for looking into that.
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | http://www.pengutronix.de/ |
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