2008/10/23 Ralf Baechle <ralf@xxxxxxxxxxxxxx>:
> I do have an ftrace implementation in the queue. Static ftrace works as
> far as I've tested but due to a restriction of the generic ftrace code the
> MIPS code for dynamic ftrace can't work on most SMP systems - basically
> only the R10000 and single core 34K SMP kernel variants have a chance to
> work. For others cache flushing requires a call to smp_call_function but
> that can't work because other CPUs are stopped at the time of the flush.
> So that still needs some sorting.
Ok, I started something but your work is more advanced.
One idea for this smp cache flush. Perhaps we could sync these when we are
out of kstop_machine (just for mips).
> Patch below.
>
> Ralf
>
> From: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
> Date: Wed, 10 Sep 2008 18:04:04 +0200
> Subject: [PATCH] [MIPS] Implement fcount support for MIPS.
>
> Signed-off-by: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
> ---
> arch/mips/Kconfig | 5 ++
> arch/mips/Makefile | 2 +
> arch/mips/kernel/Makefile | 2 +
> arch/mips/kernel/ftrace.c | 118 +++++++++++++++++++++++++++++++++++++
> arch/mips/kernel/mips_ksyms.c | 6 ++
> arch/mips/lib/Makefile | 2 +
> arch/mips/lib/mcount.S | 128 +++++++++++++++++++++++++++++++++++++++++
> include/asm-mips/ftrace.h | 14 +++++
> 8 files changed, 277 insertions(+), 0 deletions(-)
>
> diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
> index 5f149b0..43202db 100644
> --- a/arch/mips/Kconfig
> +++ b/arch/mips/Kconfig
> @@ -1,6 +1,7 @@
> config MIPS
> bool
> default y
> + select HAVE_FTRACE
> select HAVE_IDE
> select HAVE_OPROFILE
> select HAVE_ARCH_KGDB
> @@ -1503,6 +1504,10 @@ config MIPS_APSP_KSPD
> "exit" syscall notifying other kernel modules the SP program is
> exiting. You probably want to say yes here.
>
> +config SYS_SUPPORTS_DYNAMIC_FTRACE
> + def_bool y
> + select HAVE_DYNAMIC_FTRACE if !SMP || CPU_R10000
> +
> config MIPS_CMP
> bool "MIPS CMP framework support"
> depends on SYS_SUPPORTS_MIPS_CMP
> diff --git a/arch/mips/Makefile b/arch/mips/Makefile
> index 7f39fd8..ae9099b 100644
> --- a/arch/mips/Makefile
> +++ b/arch/mips/Makefile
> @@ -14,7 +14,9 @@
>
> KBUILD_DEFCONFIG := ip22_defconfig
>
> +ifndef CONFIG_FTRACE
> cflags-y := -ffunction-sections
> +endif
>
> #
> # Select the object file format to substitute into the linker script.
> diff --git a/arch/mips/kernel/Makefile b/arch/mips/kernel/Makefile
> index d9da711..ea730e0 100644
> --- a/arch/mips/kernel/Makefile
> +++ b/arch/mips/kernel/Makefile
> @@ -43,6 +43,8 @@ obj-$(CONFIG_CPU_TX39XX) += r2300_fpu.o r2300_switch.o
> obj-$(CONFIG_CPU_TX49XX) += r4k_fpu.o r4k_switch.o
> obj-$(CONFIG_CPU_VR41XX) += r4k_fpu.o r4k_switch.o
>
> +obj-$(CONFIG_DYNAMIC_FTRACE) += ftrace.o
> +
> obj-$(CONFIG_SMP) += smp.o
> obj-$(CONFIG_SMP_UP) += smp-up.o
>
> diff --git a/arch/mips/kernel/ftrace.c b/arch/mips/kernel/ftrace.c
> new file mode 100644
> index 0000000..e24ae47
> --- /dev/null
> +++ b/arch/mips/kernel/ftrace.c
> @@ -0,0 +1,118 @@
> +#include <linux/ftrace.h>
> +#include <linux/init.h>
> +#include <linux/uaccess.h>
> +
> +#include <asm/cacheflush.h>
> +#include <asm/sgidefs.h>
> +#include <asm/inst.h>
> +#include <asm/ftrace.h>
> +
> +/*
> + * On O32 the gcc generated code sequence to invoke _mcount looks like
> + *
> + * move $1, $31 # save current return address
> + * subu $sp, $sp, 8 # _mcount pops 2 words from stack
> + * jal _mcount
> + * j $31
> + *
> + * If the _mcount call is nop'ed out we still need to pop the stack frame.
> + * So we use an addiu $sp, $sp, 8 instead. NABI doesn't allocate frames in
> + * such a nonsenical way so a normal nop does the magic.
> + */
> +static const union mips_instruction ftrace_nop = {
> +#if _MIPS_SIM == _MIPS_SIM_ABI32
> + .i_format.opcode = addiu_op, /* addiu $sp, $sp, 8 */
> + .i_format.rs = 29,
> + .i_format.rt = 29,
> + .i_format.simmediate = 8
> +#else
> + .word = 0 /* normal nop */
> +#endif
> +};
> +
> +notrace unsigned char *ftrace_nop_replace(void)
> +{
> + return (unsigned char *) ftrace_nop.byte;
> +}
> +
> +notrace unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
> +{
> + static union mips_instruction inst;
> +
> + if (unlikely(ip ^ addr) >> 26) {
> + WARN_ON_ONCE(1);
> + return NULL;
> + }
> +
> + inst.j_format.opcode = jal_op;
> + inst.j_format.target = addr >> 2;
> +
> + return (unsigned char *) &inst;
> +}
> +
> +notrace int
> +ftrace_modify_code(unsigned long ip, unsigned char *old_code,
> + unsigned char *new_code)
> +{
> + unsigned int old = *(unsigned int *) old_code;
> + unsigned int new = *(unsigned int *) new_code;
> + unsigned int replaced;
> + int err;
> +
> + err = __get_user(replaced, (unsigned int *) ip);
> + if (unlikely(err))
> + return 1;
> +
> + err = __put_user(new, (unsigned int *) ip);
> + if (unlikely(err))
> + return 1;
> +
> + if (unlikely(replaced != old && replaced != new))
> + return 2;
> +
> + /*
> + * This is broken. We need to flush the icache on all processors
> + * but can't because ftrace_modify_code is executed with interrupts
> + * disabled ...
> + */
> + local_flush_icache_range(ip, ip + MCOUNT_INSN_SIZE);
> +
> + return 0;
> +}
> +
> +notrace 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(ip, (unsigned long)func);
> + ret = ftrace_modify_code(ip, old, new);
> +
> + return ret;
> +}
> +
> +notrace int ftrace_mcount_set(unsigned long *data)
> +{
> + unsigned long ip = (unsigned long) &mcount_call;
> + unsigned long *addr = data;
> + unsigned char old[MCOUNT_INSN_SIZE], *new;
> +
> + /*
> + * Replace the mcount stub with a pointer to the
> + * ip recorder function.
> + */
> + memcpy(old, &mcount_call, MCOUNT_INSN_SIZE);
> + new = ftrace_call_replace(ip, *addr);
> + *addr = ftrace_modify_code(ip, old, new);
> +
> + return 0;
> +}
> +
> +int __init ftrace_dyn_arch_init(void *data)
> +{
> + ftrace_mcount_set(data);
> +
> + return 0;
> +}
> diff --git a/arch/mips/kernel/mips_ksyms.c b/arch/mips/kernel/mips_ksyms.c
> index 225755d..18f5556 100644
> --- a/arch/mips/kernel/mips_ksyms.c
> +++ b/arch/mips/kernel/mips_ksyms.c
> @@ -11,6 +11,7 @@
> #include <linux/interrupt.h>
> #include <linux/module.h>
> #include <asm/checksum.h>
> +#include <asm/ftrace.h>
> #include <asm/pgtable.h>
> #include <asm/uaccess.h>
>
> @@ -51,3 +52,8 @@ EXPORT_SYMBOL(csum_partial_copy_nocheck);
> EXPORT_SYMBOL(__csum_partial_copy_user);
>
> EXPORT_SYMBOL(invalid_pte_table);
> +
> +#ifdef CONFIG_FTRACE
> +/* _mcount is defined in assembly */
> +EXPORT_SYMBOL(_mcount);
> +#endif
> diff --git a/arch/mips/lib/Makefile b/arch/mips/lib/Makefile
> index 8810dfb..c9ec0c3 100644
> --- a/arch/mips/lib/Makefile
> +++ b/arch/mips/lib/Makefile
> @@ -27,5 +27,7 @@ obj-$(CONFIG_CPU_TX39XX) += r3k_dump_tlb.o
> obj-$(CONFIG_CPU_TX49XX) += dump_tlb.o
> obj-$(CONFIG_CPU_VR41XX) += dump_tlb.o
>
> +obj-$(CONFIG_FTRACE) += mcount.o
> +
> # libgcc-style stuff needed in the kernel
> obj-y += ashldi3.o ashrdi3.o cmpdi2.o lshrdi3.o ucmpdi2.o
> diff --git a/arch/mips/lib/mcount.S b/arch/mips/lib/mcount.S
> new file mode 100644
> index 0000000..9817ce6
> --- /dev/null
> +++ b/arch/mips/lib/mcount.S
> @@ -0,0 +1,128 @@
> +#include <asm/regdef.h>
> +#include <asm/ftrace.h>
> +#include <asm/asm.h>
> +
> +/*
> + * The problem here is that _mcount() is not a normal function. It does
> + * not obey the calling conventions of a normal function. It takes its
> + * arguments in $at and $ra, and it is required to preserve $ra - and most
> + * other registers, in fact, if I remember correctly. The arguments have
> + * not yet been saved. You need to do this. Another bizarreness is that
> + * the caller needs to pop an extra 8 bytes for the O32.
> + */
That's the information I missed. I actually had some trouble to find
the parent ip.
The only solution to find it for me was to walk through the stack with
the function
__kernel_text_address until it returns non-zero. That was ugly because fairly
bad for performances and a function pointer could have been put in the stack and
so been considered as a return address.
I should have a look at a disassembly dump after a building with -pg
> +#if _MIPS_SIM == _ABIO32
> +#define POP_EXTRA 8
> +#define ARG_SAVE 16
> +#define N_ARG_REGS 4
> +#else
> +#define POP_EXTRA 0
> +#define ARG_SAVE 0
> +#define N_ARG_REGS 8
> +#endif
> +
> + .macro save_mcount_frame
> + PTR_SUBU sp, sp, ARG_SAVE + (N_ARG_REGS + 4) * LONGSIZE
> + LONG_S AT, ARG_SAVE + 0 * LONGSIZE(sp)
> + LONG_S ra, ARG_SAVE + 1 * LONGSIZE(sp)
> + LONG_S a0, ARG_SAVE + 2 * LONGSIZE(sp)
> + LONG_S a1, ARG_SAVE + 3 * LONGSIZE(sp)
> + LONG_S a2, ARG_SAVE + 4 * LONGSIZE(sp)
> + LONG_S a3, ARG_SAVE + 5 * LONGSIZE(sp)
> +#if _MIPS_SIM == _ABI64
> + LONG_S a4, ARG_SAVE + 6 * LONGSIZE(sp)
> + LONG_S a5, ARG_SAVE + 7 * LONGSIZE(sp)
> + LONG_S a6, ARG_SAVE + 8 * LONGSIZE(sp)
> + LONG_S a7, ARG_SAVE + 9 * LONGSIZE(sp)
> +#endif
> + LONG_S v0, ARG_SAVE + (2 + N_ARG_REGS) * LONGSIZE(sp)
> + .endm
> +
> + .macro restore_mcount_frame
> + LONG_L AT, ARG_SAVE + 0 * LONGSIZE(sp)
> + LONG_L ra, ARG_SAVE + 1 * LONGSIZE(sp)
> + LONG_L a0, ARG_SAVE + 2 * LONGSIZE(sp)
> + LONG_L a1, ARG_SAVE + 3 * LONGSIZE(sp)
> + LONG_L a2, ARG_SAVE + 4 * LONGSIZE(sp)
> + LONG_L a3, ARG_SAVE + 5 * LONGSIZE(sp)
> +#if _MIPS_SIM == _ABI64
> + LONG_L a4, ARG_SAVE + 6 * LONGSIZE(sp)
> + LONG_L a5, ARG_SAVE + 7 * LONGSIZE(sp)
> + LONG_L a6, ARG_SAVE + 8 * LONGSIZE(sp)
> + LONG_L a7, ARG_SAVE + 9 * LONGSIZE(sp)
> +#endif
> + LONG_L v0, ARG_SAVE + (2 + N_ARG_REGS) * LONGSIZE(sp)
> + PTR_ADDU sp, sp, ARG_SAVE + (N_ARG_REGS + 4) * LONGSIZE + POP_EXTRA
> + .endm
> +
> +#ifdef CONFIG_DYNAMIC_FTRACE
> +
> +LEAF(_mcount)
> + .set push
> + .set noreorder
> + .set noat
> + save_mcount_frame
> + PTR_SUBU a0, ra, 2 * MCOUNT_INSN_SIZE
> +
> +FEXPORT(mcount_call)
> + jal ftrace_stub
> + nop
> +
> + restore_mcount_frame
> + jr ra
> + move ra, AT
> + .set pop
> + END(_mcount)
> +
> +LEAF(ftrace_caller)
> + .set push
> + .set noreorder
> + .set noat
> + save_mcount_frame
> + PTR_SUBU a0, ra, 2 * MCOUNT_INSN_SIZE
> + move a1, AT
> +
> +FEXPORT(ftrace_call)
> + jal ftrace_stub
> + nop
> +
> + restore_mcount_frame
> + jr ra
> + move ra, AT
> + .set pop
> + END(ftrace_caller)
> +
> +#else
> +
> +LEAF(_mcount)
> + .set push
> + .set noreorder
> + .set noat
> + PTR_L t0, ftrace_trace_function
> + PTR_LA t1, ftrace_stub
> + bne t0, t1, trace
> + nop
> +
> +#if POP_EXTRA
> + PTR_ADDIU sp, sp, 8
> +#endif
> + jr ra
> + move ra, AT
> +
> +trace:
> + save_mcount_frame
> + PTR_SUBU a0, ra, 2 * MCOUNT_INSN_SIZE
> + move a1, AT
> + jalr t0
> + nop
> + restore_mcount_frame
> + jr ra
> + move ra, AT
> + .set pop
> + END(_mcount)
> +
> +#endif /* !CONFIG_DYNAMIC_FTRACE */
> +
> +LEAF(ftrace_stub)
> + jr ra
> + END(ftrace_stub)
> diff --git a/include/asm-mips/ftrace.h b/include/asm-mips/ftrace.h
> new file mode 100644
> index 0000000..f0479ce
> --- /dev/null
> +++ b/include/asm-mips/ftrace.h
> @@ -0,0 +1,14 @@
> +#ifndef __ASM_FTRACE_H
> +#define __ASM_FTRACE_H
> +
> +#ifdef CONFIG_FTRACE
> +#define MCOUNT_ADDR ((long)(_mcount))
> +#define MCOUNT_INSN_SIZE 4 /* sizeof mcount call */
> +
> +#ifndef __ASSEMBLY__
> +extern void _mcount(void);
> +#endif
> +
> +#endif /* CONFIG_FTRACE */
> +
> +#endif /* __ASM_FTRACE_H */
>
I can only test through qemu and I usually choose a malta emulation.
If you want some help
for testing or things like that. Don't hesitate.
