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Re: [PATCH v1 2/5] mips dynamic function tracer support

To: wuzhangjin@gmail.com
Subject: Re: [PATCH v1 2/5] mips dynamic function tracer support
From: Steven Rostedt <rostedt@goodmis.org>
Date: Thu, 28 May 2009 21:24:55 -0400 (EDT)
Cc: linux-mips@linux-mips.org, linux-kernel@vger.kernel.org, Wu Zhangjin <wuzj@lemote.com>, Ralf Baechle <ralf@linux-mips.org>, Ingo Molnar <mingo@elte.hu>, Andrew Morton <akpm@linux-foundation.org>, Thomas Gleixner <tglx@linutronix.de>, Nicholas Mc Guire <der.herr@hofr.at>
In-reply-to: <de2cff602f0b0251ea1878ff83e059437973b6fd.1243543471.git.wuzj@lemote.com>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <cover.1243543471.git.wuzj@lemote.com> <de2cff602f0b0251ea1878ff83e059437973b6fd.1243543471.git.wuzj@lemote.com>
Sender: linux-mips-bounce@linux-mips.org
User-agent: Alpine 2.00 (DEB 1167 2008-08-23)
On Fri, 29 May 2009, wuzhangjin@gmail.com wrote:

> From: Wu Zhangjin <wuzj@lemote.com>
> 
> dynamic function tracer need to replace "nop" to "jumps & links" and
> something reversely.
> 
> Signed-off-by: Wu Zhangjin <wuzj@lemote.com>
> ---
>  arch/mips/Kconfig              |    3 +
>  arch/mips/include/asm/ftrace.h |   10 ++
>  arch/mips/kernel/Makefile      |    2 +
>  arch/mips/kernel/ftrace.c      |  217 
> ++++++++++++++++++++++++++++++++++++++++
>  arch/mips/kernel/mcount.S      |   31 ++++++
>  scripts/Makefile.build         |    1 +
>  scripts/recordmcount.pl        |   32 +++++-
>  7 files changed, 290 insertions(+), 6 deletions(-)
>  create mode 100644 arch/mips/kernel/ftrace.c
> 
> diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
> index d5c01ca..0c00536 100644
> --- a/arch/mips/Kconfig
> +++ b/arch/mips/Kconfig
> @@ -6,6 +6,9 @@ config MIPS
>       select HAVE_ARCH_KGDB
>       select HAVE_FUNCTION_TRACER
>       select HAVE_FUNCTION_TRACE_MCOUNT_TEST
> +     select HAVE_DYNAMIC_FTRACE
> +     select HAVE_FTRACE_MCOUNT_RECORD
> +     select HAVE_FTRACE_NMI_ENTER if DYNAMIC_FTRACE
>       # Horrible source of confusion.  Die, die, die ...
>       select EMBEDDED
>       select RTC_LIB
> diff --git a/arch/mips/include/asm/ftrace.h b/arch/mips/include/asm/ftrace.h
> index 5f8ebcf..b4970c9 100644
> --- a/arch/mips/include/asm/ftrace.h
> +++ b/arch/mips/include/asm/ftrace.h
> @@ -19,6 +19,16 @@
>  extern void _mcount(void);
>  #define mcount _mcount
>  
> +#ifdef CONFIG_DYNAMIC_FTRACE
> +/* reloction of mcount call site is the same as the address */
> +static inline unsigned long ftrace_call_adjust(unsigned long addr)
> +{
> +     return addr;
> +}
> +
> +struct dyn_arch_ftrace {
> +};
> +#endif /*  CONFIG_DYNAMIC_FTRACE */
>  #endif /* __ASSEMBLY__ */
>  #endif /* CONFIG_FUNCTION_TRACER */
>  #endif /* _ASM_MIPS_FTRACE_H */
> diff --git a/arch/mips/kernel/Makefile b/arch/mips/kernel/Makefile
> index d167dde..6b1a8a5 100644
> --- a/arch/mips/kernel/Makefile
> +++ b/arch/mips/kernel/Makefile
> @@ -11,6 +11,7 @@ obj-y               += cpu-probe.o branch.o entry.o genex.o 
> irq.o process.o \
>  ifdef CONFIG_FUNCTION_TRACER
>  # Do not profile debug and lowlevel utilities
>  CFLAGS_REMOVE_mcount.o = -pg
> +CFLAGS_REMOVE_ftrace.o = -pg
>  CFLAGS_REMOVE_early_printk.o = -pg
>  endif
>  
> @@ -31,6 +32,7 @@ obj-$(CONFIG_STACKTRACE)    += stacktrace.o
>  obj-$(CONFIG_MODULES)                += mips_ksyms.o module.o
>  
>  obj-$(CONFIG_FUNCTION_TRACER)        += mcount.o
> +obj-$(CONFIG_FUNCTION_TRACER)        += ftrace.o
>  
>  obj-$(CONFIG_CPU_LOONGSON2)  += r4k_fpu.o r4k_switch.o
>  obj-$(CONFIG_CPU_MIPS32)     += r4k_fpu.o r4k_switch.o
> diff --git a/arch/mips/kernel/ftrace.c b/arch/mips/kernel/ftrace.c
> new file mode 100644
> index 0000000..827c128
> --- /dev/null
> +++ b/arch/mips/kernel/ftrace.c
> @@ -0,0 +1,217 @@
> +/*
> + * Code for replacing ftrace calls with jumps.
> + *
> + * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
> + * Copyright (C) 2009 DSLab, Lanzhou University, China
> + * Author: Wu Zhangjin <wuzj@lemote.com>
> + *
> + * Thanks goes to Steven Rostedt for writing the original x86 version.
> + */
> +
> +#include <linux/spinlock.h>
> +#include <linux/hardirq.h>
> +#include <linux/uaccess.h>
> +#include <linux/percpu.h>
> +#include <linux/sched.h>
> +#include <linux/init.h>
> +#include <linux/list.h>
> +#include <linux/ftrace.h>
> +
> +#include <asm/cacheflush.h>
> +#include <asm/ftrace.h>
> +#include <asm/asm.h>
> +#include <asm/unistd.h>
> +
> +#ifdef CONFIG_DYNAMIC_FTRACE
> +
> +#define JAL 0x0c000000       /* jump & link: ip --> ra, jump to target */
> +#define ADDR_MASK 0x03ffffff /*  op_code|addr : 31...26|25 ....0 */
> +
> +static unsigned int ftrace_nop = 0x00000000;
> +
> +static unsigned char *ftrace_call_replace(unsigned long op_code,
> +                                       unsigned long addr)
> +{
> +    static unsigned int op;
> +
> +    op = op_code | ((addr >> 2) & ADDR_MASK);
> +
> +    return (unsigned char *) &op;
> +}
> +
> +static atomic_t nmi_running = ATOMIC_INIT(0);
> +static int mod_code_status;  /* holds return value of text write */
> +static int mod_code_write;   /* set when NMI should do the write */
> +static void *mod_code_ip;    /* holds the IP to write to */
> +static void *mod_code_newcode;       /* holds the text to write to the IP */
> +
> +static unsigned nmi_wait_count;
> +static atomic_t nmi_update_count = ATOMIC_INIT(0);
> +
> +int ftrace_arch_read_dyn_info(char *buf, int size)
> +{
> +    int r;
> +
> +    r = snprintf(buf, size, "%u %u",
> +              nmi_wait_count, atomic_read(&nmi_update_count));
> +    return r;
> +}
> +
> +static void ftrace_mod_code(void)
> +{
> +    /*
> +     * Yes, more than one CPU process can be writing to mod_code_status.
> +     *    (and the code itself)
> +     * But if one were to fail, then they all should, and if one were
> +     * to succeed, then they all should.
> +     */
> +    mod_code_status = probe_kernel_write(mod_code_ip, mod_code_newcode,
> +                                      MCOUNT_INSN_SIZE);
> +
> +    /* if we fail, then kill any new writers */
> +    if (mod_code_status)
> +             mod_code_write = 0;
> +}
> +
> +void ftrace_nmi_enter(void)
> +{
> +    atomic_inc(&nmi_running);
> +    /* Must have nmi_running seen before reading write flag */
> +    smp_mb();
> +    if (mod_code_write) {
> +             ftrace_mod_code();
> +             atomic_inc(&nmi_update_count);
> +    }
> +}
> +
> +void ftrace_nmi_exit(void)
> +{
> +    /* Finish all executions before clearing nmi_running */
> +    smp_wmb();
> +    atomic_dec(&nmi_running);
> +}
> +
> +static void wait_for_nmi(void)
> +{
> +    int waited = 0;
> +
> +    while (atomic_read(&nmi_running)) {
> +             waited = 1;
> +             cpu_relax();
> +    }
> +
> +    if (waited)
> +             nmi_wait_count++;
> +}
> +
> +static int do_ftrace_mod_code(unsigned long ip, void *new_code)
> +{
> +    mod_code_ip = (void *) ip;
> +    mod_code_newcode = new_code;
> +
> +    /* The buffers need to be visible before we let NMIs write them */
> +    smp_wmb();
> +
> +    mod_code_write = 1;
> +
> +    /* Make sure write bit is visible before we wait on NMIs */
> +    smp_mb();
> +
> +    wait_for_nmi();
> +
> +    /* Make sure all running NMIs have finished before we write the code */
> +    smp_mb();
> +
> +    ftrace_mod_code();
> +
> +    /* Make sure the write happens before clearing the bit */
> +    smp_wmb();
> +
> +    mod_code_write = 0;
> +
> +    /* make sure NMIs see the cleared bit */
> +    smp_mb();
> +
> +    wait_for_nmi();
> +
> +    return mod_code_status;
> +}

Hmm, this is basically exactly the same as x86's version. I wounder if we 
should make a helper function in generic code to let archs use it. We can 
put the do_ftrace_mod_code into kernel/trace/ftrace.c and have weak 
functions for the ftrace_mod_code. If the arch needs this to handle NMIs, 
then it can use it. This code was tricky to write, and I would hate to 
have it duplicated in every arch.

> +
> +static unsigned char *ftrace_nop_replace(void)
> +{
> +    return (unsigned char *) &ftrace_nop;
> +}
> +
> +static int
> +ftrace_modify_code(unsigned long ip, unsigned char *old_code,
> +                unsigned char *new_code)
> +{
> +    unsigned char replaced[MCOUNT_INSN_SIZE];
> +
> +    /*
> +     * Note: Due to modules and __init, code can
> +     *  disappear and change, we need to protect against faulting
> +     *  as well as code changing. We do this by using the
> +     *  probe_kernel_* functions.

hehe, this is an old comment. We don't touch __init sections anymore. I 
need to remove it from the x86 file.

> +     *
> +     * No real locking needed, this code is run through
> +     * kstop_machine, or before SMP starts.
> +     */
> +
> +    /* read the text we want to modify */
> +    if (probe_kernel_read(replaced, (void *) ip, MCOUNT_INSN_SIZE))
> +             return -EFAULT;
> +
> +    /* Make sure it is what we expect it to be */
> +    if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0)
> +             return -EINVAL;
> +
> +    /* replace the text with the new text */
> +    if (do_ftrace_mod_code(ip, new_code))
> +             return -EPERM;
> +
> +    return 0;
> +}
> +
> +int ftrace_make_nop(struct module *mod,
> +                 struct dyn_ftrace *rec, unsigned long addr)
> +{
> +    unsigned char *new, *old;
> +
> +    old = ftrace_call_replace(JAL, addr);
> +    new = ftrace_nop_replace();
> +
> +    return ftrace_modify_code(rec->ip, old, new);
> +}
> +
> +int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
> +{
> +    unsigned char *new, *old;
> +
> +    old = ftrace_nop_replace();
> +    new = ftrace_call_replace(JAL, addr);
> +
> +    return ftrace_modify_code(rec->ip, old, new);
> +}
> +
> +int ftrace_update_ftrace_func(ftrace_func_t func)
> +{
> +    unsigned long ip = (unsigned long) (&ftrace_call);
> +    unsigned char old[MCOUNT_INSN_SIZE], *new;
> +    int ret;
> +
> +    memcpy(old, &ftrace_call, MCOUNT_INSN_SIZE);
> +    new = ftrace_call_replace(JAL, (unsigned long) func);
> +    ret = ftrace_modify_code(ip, old, new);
> +
> +    return ret;
> +}
> +
> +int __init ftrace_dyn_arch_init(void *data)
> +{
> +    /* The return code is retured via data */
> +    *(unsigned long *) data = 0;

egad, I need to clean that up too. I should return the true error code 
with ret. That is legacy from the first version of the dynamic ftrace 
code.

This review is showing all the flaws of my own work ;-)

> +
> +    return 0;
> +}
> +#endif                               /* CONFIG_DYNAMIC_FTRACE */
> diff --git a/arch/mips/kernel/mcount.S b/arch/mips/kernel/mcount.S
> index 268724e..ce8a0ba 100644
> --- a/arch/mips/kernel/mcount.S
> +++ b/arch/mips/kernel/mcount.S
> @@ -67,6 +67,35 @@
>       move ra, $1
>       .endm
>  
> +#ifdef CONFIG_DYNAMIC_FTRACE
> +
> +LEAF(_mcount)
> +     RESTORE_SP_FOR_32BIT
> +     RETURN_BACK
> +     END(_mcount)
> +
> +NESTED(ftrace_caller, PT_SIZE, ra)
> +     RESTORE_SP_FOR_32BIT
> +     lw      t0, function_trace_stop
> +     bnez    t0, ftrace_stub
> +     nop
> +
> +     MCOUNT_SAVE_REGS
> +
> +     MCOUNT_SET_ARGS
> +     .globl ftrace_call
> +ftrace_call:
> +     jal     ftrace_stub
> +     nop
> +
> +     MCOUNT_RESTORE_REGS
> +     .globl ftrace_stub
> +ftrace_stub:
> +     RETURN_BACK
> +     END(ftrace_caller)
> +
> +#else        /* ! CONFIG_DYNAMIC_FTRACE */
> +
>  NESTED(_mcount, PT_SIZE, ra)
>       RESTORE_SP_FOR_32BIT
>       PTR_L   t0, function_trace_stop
> @@ -94,5 +123,7 @@ ftrace_stub:
>       RETURN_BACK
>       END(_mcount)
>  
> +#endif       /* ! CONFIG_DYNAMIC_FTRACE */
> +
>       .set at
>       .set reorder
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index 5c4b7a4..548d575 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -207,6 +207,7 @@ endif
>  
>  ifdef CONFIG_FTRACE_MCOUNT_RECORD
>  cmd_record_mcount = perl $(srctree)/scripts/recordmcount.pl "$(ARCH)" \
> +     "$(if $(CONFIG_CPU_BIG_ENDIAN),big,little)" \
>       "$(if $(CONFIG_64BIT),64,32)" \
>       "$(OBJDUMP)" "$(OBJCOPY)" "$(CC)" "$(LD)" "$(NM)" "$(RM)" "$(MV)" \
>       "$(if $(part-of-module),1,0)" "$(@)";

This big/little endian addition, I would like in its own patch.

> diff --git a/scripts/recordmcount.pl b/scripts/recordmcount.pl
> index 409596e..e963948 100755
> --- a/scripts/recordmcount.pl
> +++ b/scripts/recordmcount.pl
> @@ -100,13 +100,13 @@ $P =~ s@.*/@@g;
>  
>  my $V = '0.1';
>  
> -if ($#ARGV < 7) {
> -     print "usage: $P arch bits objdump objcopy cc ld nm rm mv is_module 
> inputfile\n";
> +if ($#ARGV < 8) {
> +     print "usage: $P arch endian bits objdump objcopy cc ld nm rm mv 
> is_module inputfile\n";
>       print "version: $V\n";
>       exit(1);
>  }
>  
> -my ($arch, $bits, $objdump, $objcopy, $cc,
> +my ($arch, $endian, $bits, $objdump, $objcopy, $cc,
>      $ld, $nm, $rm, $mv, $is_module, $inputfile) = @ARGV;
>  
>  # This file refers to mcount and shouldn't be ftraced, so lets' ignore it
> @@ -213,6 +213,26 @@ if ($arch eq "x86_64") {
>      if ($is_module eq "0") {
>          $cc .= " -mconstant-gp";
>      }
> +
> +} elsif ($arch eq "mips") {
> +     $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s_mcount\$";
> +     $objdump .= " -Melf-trad".$endian."mips ";
> +
> +     if ($endian eq "big") {
> +             $endian = " -EB ";
> +             $ld .= " -melf".$bits."btsmip";
> +     } else {
> +             $endian = " -EL ";
> +             $ld .= " -melf".$bits."ltsmip";
> +     }
> +
> +     $cc .= " -mno-abicalls -fno-pic -mabi=" . $bits . $endian;
> +    $ld .= $endian;
> +
> +    if ($bits == 64) {
> +             $type = ".dword";
> +    }

The mips addition to the recordmcount.pl is OK to keep with this patch.

> +
>  } else {
>      die "Arch $arch is not supported with CONFIG_FTRACE_MCOUNT_RECORD";
>  }
> @@ -441,12 +461,12 @@ if ($#converts >= 0) {
>      #
>      # Step 5: set up each local function as a global
>      #
> -    `$objcopy $globallist $inputfile $globalobj`;
> +    `$objcopy $globallist $inputfile $globalobj 2>&1 >/dev/null`;

Are these spitting out errors?

-- Steve

>  
>      #
>      # Step 6: Link the global version to our list.
>      #
> -    `$ld -r $globalobj $mcount_o -o $globalmix`;
> +    `$ld -r $globalobj $mcount_o -o $globalmix 2>&1 >/dev/null`;
>  
>      #
>      # Step 7: Convert the local functions back into local symbols
> @@ -454,7 +474,7 @@ if ($#converts >= 0) {
>      `$objcopy $locallist $globalmix $inputfile`;
>  
>      # Remove the temp files
> -    `$rm $globalobj $globalmix`;
> +    `$rm $globalobj $globalmix 2>&1 >/dev/null`;
>  
>  } else {
>  
> -- 
> 1.6.0.4
> 
> 

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