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

From: Wu Zhangjin
Date: Fri May 29 2009 - 02:37:09 EST

On Thu, 2009-05-28 at 21:24 -0400, Steven Rostedt wrote:
> On Fri, 29 May 2009, wuzhangjin@xxxxxxxxx wrote:
>
> > From: Wu Zhangjin <wuzj@xxxxxxxxxx>
> >
> > dynamic function tracer need to replace "nop" to "jumps & links" and
> > something reversely.
> >
> > Signed-off-by: Wu Zhangjin <wuzj@xxxxxxxxxx>
> > ---
> > 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@xxxxxxxxxx>
> > + * Copyright (C) 2009 DSLab, Lanzhou University, China
> > + * Author: Wu Zhangjin <wuzj@xxxxxxxxxx>
> > + *
> > + * 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.
>

so, when will you put do_ftrace_mod_code into kernel/trace/ftrace.c?
i just checked the powerpc version, seems something different, so, we
should handle it carefully and tune the relative arch-dependent parts?

> > +
> > +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.
>

Removed, this is the same in powerpc version.

> > + *
> > + * 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 ;-)
>

Yeap, most of it is copied from your original x86 version.

there are really lots of duplications among different arch-specific
versions, need to cleanup carefully, and should we write something like
a helper document for people developing arch-specific version?

> > +
> > + 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.
>

okay, will split it out later.

> > 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?
>

no errors, but some warnings.

seems some files not have _mcount(ooh, I did this patch about two months
ago, so not remember the _real_ reason now), so there will some
complaint about "No such file ...", this fix just make it not complain
again.

> -- 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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