linux-kernel - Re: [PATCH 3/5] jump label: x86 support

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Date:	Mon, 22 Mar 2010 12:40:25 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Jason Baron <jbaron@...hat.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu,
	mathieu.desnoyers@...ymtl.ca, hpa@...or.com, tglx@...utronix.de,
	andi@...stfloor.org, roland@...hat.com, rth@...hat.com,
	mhiramat@...hat.com, fweisbec@...il.com
Subject: Re: [PATCH 3/5] jump label: x86 support

On Mon, 2010-03-22 at 12:07 -0400, Jason Baron wrote:
> add x86 support for jump label. I'm keeping this patch separate so its clear to
> arch maintainers what was required for x86 support this new feature. hopefully,
> it wouldn't be too painful for other arches.
> 
> Signed-off-by: Jason Baron <jbaron@...hat.com>


> +#ifdef __HAVE_ARCH_JUMP_LABEL
> +
> +# ifdef CONFIG_X86_64
> +#  define JUMP_LABEL_NOP P6_NOP5
> +# else
> +#  define JUMP_LABEL_NOP ".byte 0xe9 \n\t .long 0\n\t"
> +# endif

Are you sure P6_NOP5 can't happen on non 64bit? Just because it is not
configured does not mean that the CPU can not handle it. Look at the
code I did in arch/x86/kernel/ftrace.c to determine what nop to use.
Maybe we can make that generic and have at boot up, the kernel determine
a proper 5byte nop.

> +
> +# define JUMP_LABEL(tag, label, cond)				\
> +	do {							\
> +		extern const char __jlstrtab_##tag[];		\
> +		asm goto("1:"					\
> +			JUMP_LABEL_NOP				\
> +			".pushsection __jump_table,  \"a\" \n\t"\
> +			_ASM_PTR "1b, %l[" #label "], %c0 \n\t" \
> +			".popsection \n\t"			\
> +			: :  "i" (__jlstrtab_##tag) :  : label);\
> +	} while (0)
> +
> +# endif
> +
> +#endif
> diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
> index 4c58352..7cd3bf4 100644
> --- a/arch/x86/kernel/Makefile
> +++ b/arch/x86/kernel/Makefile
> @@ -32,7 +32,7 @@ GCOV_PROFILE_paravirt.o		:= n
>  obj-y			:= process_$(BITS).o signal.o entry_$(BITS).o
>  obj-y			+= traps.o irq.o irq_$(BITS).o dumpstack_$(BITS).o
>  obj-y			+= time.o ioport.o ldt.o dumpstack.o
> -obj-y			+= setup.o x86_init.o i8259.o irqinit.o
> +obj-y			+= setup.o x86_init.o i8259.o irqinit.o jump_label.o
>  obj-$(CONFIG_X86_VISWS)	+= visws_quirks.o
>  obj-$(CONFIG_X86_32)	+= probe_roms_32.o
>  obj-$(CONFIG_X86_32)	+= sys_i386_32.o i386_ksyms_32.o
> diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c
> new file mode 100644
> index 0000000..7fc4f84
> --- /dev/null
> +++ b/arch/x86/kernel/jump_label.c
> @@ -0,0 +1,53 @@
> +/*
> + * jump label x86 support
> + *
> + * Copyright (C) 2009 Jason Baron <jbaron@...hat.com>
> + *
> + */
> +#include <linux/jump_label.h>
> +#include <linux/memory.h>
> +#include <linux/uaccess.h>
> +#include <linux/module.h>
> +#include <linux/list.h>
> +#include <linux/jhash.h>
> +#include <linux/cpu.h>
> +#include <asm/kprobes.h>
> +
> +#ifdef __HAVE_ARCH_JUMP_LABEL
> +
> +union jump_code_union {
> +	char code[RELATIVEJUMP_SIZE];
> +	struct {
> +		char jump;
> +		int offset;
> +	} __attribute__((packed));
> +};
> +
> +void arch_jump_label_transform(struct jump_entry *entry, enum jump_label_type type)
> +{
> +	union jump_code_union code;
> +
> +	if (type == JUMP_LABEL_ENABLE) {
> +		code.jump = 0xe9;
> +		code.offset = entry->target - (entry->code + RELATIVEJUMP_SIZE);
> +	} else {
> +#ifdef CONFIG_X86_64
> +		/* opcode for P6_NOP5 */
> +		code.code[0] = 0x0f;
> +		code.code[1] = 0x1f;
> +		code.code[2] = 0x44;
> +		code.code[3] = 0x00;
> +		code.code[4] = 0x00;
> +#else
> +		code.jump = 0xe9;
> +		code.offset = 0;
> +#endif

Same here, and this should also just use the JUMP_LABEL_NOP insead of
spelling it out as it does here. memcpy should work.

-- Steve


> +	}
> +	get_online_cpus();
> +	mutex_lock(&text_mutex);
> +	text_poke_smp((void *)entry->code, &code, RELATIVEJUMP_SIZE);
> +	mutex_unlock(&text_mutex);
> +	put_online_cpus();
> +}
> +
> +#endif


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